Davos Atmosphere and
Cryosphere Assembly DACA-13
Air, Ice & Process Interactions
An IUGG (IAMAS & IACS) Event
July 8-12, 2013
Davos, Switzerland
www.daca-13.org
Abstract Proceedings
Table of Contents
Pages 3 – 1152
Abstracts for oral presentations and posters with regular submission, following
the order of the week’s program
Pages 1153 – 1177
Abstracts for oral presentations and posters that were cancelled before 14
June 2013, following the order of the week’s program
Pages 1178 - 1189
Abstracts for posters with late submission, following the order of the week’s
program
Presenting authors are underlined.
Page | 2
A4.1a - Accurately Quantifying Changes in Sea Ice using Satellite Remote
Sensing
08.07.2013 10:15-11:45, Sanada II
1263
Accuracy of satellite passive microwave sea ice time series data
1
Josefino Comiso
1
Cryospheric Sciences Laboratory, NASA Goddard Space Flight Center, Greenbelt, United States
Long term satellite data sets on the sea ice cover are made possible only by putting together data from
similar sensons that may not have compatible calibration, resolution and other characteristics. The 1channel Electrically Scanning Microwave Radiometer (ESMR) launched in 1972 provided the first
complete coverate of the sea ice cover at a good temporal resolution. Because of data gaps and
retrieval problems, however, time series studies usually starts with data from the Scanning
Multichannel Microwave Radiometer (SMMR) which provided good data from November 1978 to
August 1987. This sensor was succeeded by a few Special Scanning Microwave Imagers (SSM/I)
which have been providing good data from July 1987 to the present. Capabilities were further
improved with the launch in 2002 of the Advance Microwave Scanning Radiometer (AMSR-E) which
has higher resolution than the other sensors. The basic parameters derived from these sensors have
been sea ice concentration which is derived using an algorithm, sea ice extent and ice area. The
uncertainty in estimating ice concentration is about 5% to 15% depending on season while that for sea
ice extent and ice area is about 5%. The strategy for change studies has been to use the best sensor
(i.e., AMSR-E) as the baseline, ensure that SSM/I and SMMR provides compatible retrievals, and the
use the latter 2 which have compatible resolution for variablity and trend studies. Using AMSR-E in
time series studies causes the introduction of a little bias because of different side-lobe effects and
higher resolution.
Page | 3
600
Sea ice concentration as an essential climate variable
1
2
3
2
4
Natalia Ivanova , Leif T. Pedersen , Thomas Lavergne , Rasmus T. Tonboe , Roberto Saldo , Marko
5
6
7
Mäkynen , Georg Heygster , Anja Rösel
1
2
Nansen Environmental and Remote Sensing Center, Bergen, Norway, Center for Ocean and Ice,
3
4
Danish Meteorological Institute, Copenhagen, Denmark, Met.no, Oslo, Norway, DTU-Space, Lyngby,
5
6
Denmark, Finnish Meteorological Institute, Helsinki, Finland, Institute of Environmental Physics,
7
University of Bremen, Bremen, Germany, University of Hamburg, Institute of Oceanography,
Hamburg, Germany
Sea ice concentration has been derived globally from satellite observations since the 1970s. A
multitude of algorithms have been developed and applied. The resulting datasets are used to monitor
the climatic decline in sea ice extent in the Arctic and the seasonal cycle in the Southern Ocean where
so far, no significant climatic trend has been observed over the almost 40 years of observations. Since
the launch of the Scanning Multichannel Microwave Radiometer on the NIMBUS-7 satellite in 1978,
data are available almost continously (with a few gaps), and spaceborne microwave radiometers will
continue to provide these data for many years through the continuation of SSMIS, AMSR and others.
Sea ice concentration is thus an excellent climate variable providing us essential information about the
state of our planet.
There is an increasing user interest in using the sea ice concentration datasets for validation and
assimilation into models. These users require more elaborate information about uncertainties in the
sea ice concentration data than hitherto available. Users also express some curiosity about the many
different datasets and algorithms, and the fact that although they concur in the large scale picture,
they differ substantially in the details.
The purpose of the ESA Climate Change Initiative´s sea ice concentration effort (which is
complemented by a sea ice thickness effort reported elsewhere) is thus to compile all available
algorithms, perform an elaborate algorithm intercomparison and validation using a standardized
reference dataset, select an appropriate (set of) algorithm(s), and produce a dataset with detailed
uncertainty estimates. Datasets for validation will be compiled into a so-called round-robin data
package that will contain satellite observations of brightness temperatures from microwave
radiometers and corresponding high quality reference sea ice concentrations from independent
sources.
Here we will report on the generation of the reference dataset and the algorithm intercomparison
efforts.
Page | 4
388
Response of passive microwave sea ice concentration algorithms to thin ice
1
1
1
2
3
Georg Heygster , Narayan Dhital , Marcus Huntemann , Roberto Saldo , Leif T. Pedersen , Natalia
4
Ivanova
1
2
Institute of Environmental Physics, University of Bremen, Bremen, Germany, Technical University of
3
4
Denmark, Lyngby, Denmark, Danish Meteorological Institute, Copenhagen, Denmark, Nansen
Environmental and Remote Sensing Center, Bergen, Norway
ESA´s Climate Change Initiative will provide an adequate, comprehensive, and timely response to the
challenging set of requirements for highly stable, long-term satellite-based time series of essential
climate variables, that have been addressed to Space Agencies via the Global Climate Observing
System (GCOS) and the Committee on Earth Observation Satellites (CEOS). Among the essential
climate variables is sea ice. The respective ESA project will provide, among other, quality-controlled
ice concentration data sets for the Arctic and Antarctic from 1979 to present, based on passive
microwave data. To this end, a set of natural (open water, 100% ice cover, thin ice) and synthetic
(15% and 85% ice cover) sea ice key conditions has been identified.
The thin ice data set has been built based on Arctic regions of the sea ice thickness retrievals from the
L-band (1.4 GHz) sensor SMOS (Soil Moisture and Ocean Salinity) in October to December 2010.
Emphasis has been put on selecting regions of ice thickness retrievals homogeneous over the
2
footprint size of the passive microwave sensors (80x80km ) and over three days. Passive microwave
satellite observations of these situations have been collected, and the response of 10 sea ice
concentration retrieval algorithms is analyzed, together with the observed brightness temperatures
they use as input variables. The sensitivity of both, brightness temperatures and sea ice
concentrations, to the ice thickness as observed with SMOS will be shown and the consequences for
sea ice concentration time series will be discussed.
Page | 5
1045
Sea ice concentration retrieval and validation
1
2
Leif Toudal Pedersen , Christian Melsheimer
1
2
Danish Meteorological Institute, Copenhagen Ø, Denmark, IUP, University of Bremen, Bremen,
Germany
Sea ice concentration (SIC) is an important climate parameter and although satellite passive
microwave observations have been available since the 1970s, development of algorithms to derive
sea ice concentration from satellite measurements have progressed along rather traditional lines of
fairly simple linear relationships between observed brightness temperatures and SIC, neglecting
surface and atmospheric variability.
This contribution will present a novel approach where we use all available microwave brightness
temperatures observed by the AMSR-2 (or previous AMSR-E) instruments to produce an integrated
retrieval of ocean, ice and atmospheric variables.
Forward models relating parameters such as cloud liquid water, atmospheric water vapour, surface
wind speed, SST, SIC and ice type to observed brightness temperatures exist and we use a piecewise
linear inversion scheme to solve the inverse problem. We validate our retrievals against the high
quality sea ice concentration dataset of ESA´s Climate Change Initiative.
Page | 6
217
Comparison of AMSR-E and SSM/I sea ice concentrations with ASPeCt ship
observations around Antarctica
1
1
1
Alexander Beitsch , Stefan Kern , Lars Kaleschke
1
Remote sensing & Assimilation, Institute of Oceanography, KlimaCampus, Hamburg, Germany
We compare passive microwave-derived sea ice concentrations (PM SIC) with shipbased
observations of sea ice concentration (OBS). OBS as one independent data set serve as ground truth
and have the ability for estimating potential biases in PM SIC. We focus on data that are based on
different retrieval algorithms applied to Advanced Microwave Scanning Radiometer-Earth Observing
System (AMSR-E, 2002-2011) and Special Sensor Microwave Imager (SSM/I, 1991-2008)
measurements. OBS are collected according to the Antarctic Sea Ice Processes and Climate
(ASPeCt) program. We assess the quality of the satellite data by calculating correlation coefficient,
root-mean-square deviation (RMSD) and bias with respect to ASPeCt OBS based on daily mean data
and standard deviation averaged along the ship track.
All retrieval algorithms based on AMSR-E data compared in this study, Comiso Bootstrap (BST),
NASA-Team 2 (NT2) and Artist Sea Ice (ASI), show correlation coefficients above 0.8 for all dates
considered (N = 320). BST and ASI do not have a significant bias, but NT2 has a bias of + 8 %. RMSD
values are different for different seasons, but generally, Comiso BST has the lowest RMSD (< 13 %).
All retrieval algorithms based on SSM/I data compared in this study, Comiso Bootstrap (BST), NASATeam (NT), OSI SAF (OSI) and Artist Sea Ice (ASI), show correlation coefficients around 0.8 for all
dates considered (N = 1028). Each of the algorithms shows a negative bias, all but NT around -2 %.
However, NT has the maximum negative bias of around -10 %. This contrasts the positive bias NT2
shows for the AMSR-E period. Again, RMSD values are different for different seasons, but generally,
Comiso BST has the lowest RMSD (< 14 %) and NT the highest RMSD (>16 %).
Page | 7
C6.1a - Properties and variability of the mountain snow cover
08.07.2013 10:15-11:45, Aspen II
1071
Do snow depth measurement at typical flat-field locations represent total snow
at catchment scale?
1,2
1,2
Thomas Grünewald , Michael Lehning
1
2
WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland, Cryos, Ecole
Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
Area wide snow cover is important for many applications ranging from meteorological or hydrological
modelling to snow cover maps as source of information for avalanche warning and winter tourism.
Such maps are usually produced by interpolating point measurements. Snow stations (flat-field
stations) are commonly located in flat, sheltered terrain with relatively homogeneous snow cover. It
can be assumed that most flat-field stations do not represent the snow cover of the surrounding area,
especially in complex terrain as present in mountain regions. In contrast to the complex terrain in the
surrounding, the snow cover at sheltered flat-field station is typically less affected by wind erosion and
redistribution of snow by avalanches. Actually, such locations can be expected to be influenced by
enhanced deposition of precipitation.
In this study we aim to quantify the representativeness of typical mountain flat-field sites. We analyze
several data sets consisting of high resolution, area-wide snow depth measurements obtained by
airborne laser scanning. From digital terrain models and snow depth maps, potential flat-field locations
are defined automatically by applying two criteria: (i) mean slope of the area (circle with 20 m radius
around the station location) < 10° and (ii) standard deviation of the snow depth in the circular area <
20 cm. We then manually identify locations exposed to the wind and exclude them from the analysis.
The snow depths form the virtual flat-fields are then compared to the mean snow depth of the
immediate vicinity of the flat field which is defined by circles with a rising area (radius 20 to 400 m) and
to the catchment mean. The investigation shows that the vast majority of stations clearly overestimate
the mean snow depth of their vicinity. However, already averaging the local measurements over
increasing radiuses (up to 400 m) significantly reduces this bias.
Page | 8
937
Observing the temporal and spatial variability of a mountain snow cover with a
network of individual snow monitoring sensors
1
1
1
Stefan Pohl , Jakob Garvelmann , Markus Weiler
1
Institute of Hydrology, University of Freiburg, Freiburg, Germany
Topography and vegetation are considered dominant factors affecting the small-scale spatial and
temporal variability of mountain snow covers. Accurate knowledge of these influences along with high
resolution meteorological forcing data is crucial for any distributed modelling of the spatio-temporal
snow cover evolution. While many innovative remote sensing techniques provide excellent data on the
spatial variability of snow cover, their temporal resolution in particular with regard to meteorological
forcing data is often lacking.
The study presented employs a network consisting of numerous standalone snow monitoring stations
that continuously monitor snow depth and the most important meteorological variables needed to
calculate a full (snow) surface energy balance. Over 100 of these stations were deployed over two
winters in three meso-scale (< 150 km²) basins in the Black Forest, a foothills type mountain region in
Southern Germany. Deployment locations were chosen to cover all relevant topographic situations
and all major land-cover types (open fields, deciduous and coniferous forests) typical for the study
area. Data showed that elevation and vegetation cover accounted for over 70% of the spatial
variability found in the snow depth and snow water equivalent (SWE). The remaining variability could
be attributed mainly to exposure, which only seemed to be relevant for open locations, and the
influence of the surrounding topography due to its sheltering effects. The continuous nature of the
measurements also made it possible to look at the development of the strength of the relationships
between SWE and, for example, elevation throughout the winter. Furthermore, the recorded
meteorological variables provide an insight into the modifying effects of topography and different types
of vegetation on the individual snowmelt energy balance terms. The results of this study should be
very helpful for improving model algorithms aimed at modeling the temporal and spatial variability in
the evolution of a mountain snow cover.
Page | 9
969
Airborne and ground-based LiDAR observations of seasonal mountain snow
properties
1,2
3
3,4
3
5
Jeffrey Deems , David C. Finnegan , Adam L. LeWinter , Eli J. Deeb , Thomas H. Painter , Ananda
6
Fowler
1
2
National Snow and Ice Data Center, Boulder, United States, NOAA Western Water Assessment,
3
Boulder, United States, US Army Corps of Engineers Cold Regions Research and Engineering
4
5
Laboratory, Hanover, United States, University of Northern Colorado, Greeley, United States, NASA
6
Jet Propulsion Laboratory, Pasadena, United States, Riegl Laser Measurement Systems GmbH,
Horn, Austria
Manual field measurement of mountain snowpack properties is time-consuming and subject to terrain
constraints, leading to difficulties with repeatability and obtaining adequate spatial resolution and
coverage. Airborne and terrestrial laser scanning provides surface elevation and reflectance
measurement at high spatial resolution over wide areas, and has recently seen an expansion of
application to snow science interests.
This presentation provides an overview of a variety of lidar mapping and measurement techniques in
use for snow measurements by our extended team. We are using ground-based laser scans of
snowpit faces for layer delineation and characterization. We combine ground-based and airborne laser
surveys for validation and bias correction of basin-scale snow depth mapping efforts. Our in-situ
ground-based system with automated control allows monitoring of snowpack volume, accumulation,
and melt, and shows potential for observing precipitation and blowing snow mass flux. These varied
applications demonstrate the potential and value of lidar technology and techniques for measuring and
monitoring properties of the highly variable mountain snowpack.
Page | 10
637
Studies of the small-scale spatial variability of alpine snowfall and snow
accumulation using an X-band polarimetric radar
1
2
3
1
Danny Scipion , Rebecca Mott , Michael Lehning , Alexis Berne
1
Environmental Remote Sensing Lab., Ecole Polytechnique Fédérale de Lausanne EPFL, Lausanne,
2
3
Switzerland, Institute for Snow and Avalanche Research, Davos, Switzerland, Laboratory of
Cryospheric Sciences, Ecole Polytechnique Fédérale de Lausanne EPFL, Lausanne, Switzerland
A mobile polarimetric X-band radar (MXPol) deployed in the vicinity of Davos (Switzerland) collected
high-resolution quantitative information on precipitation for the winter seasons of 2009/2010 and
2010/2011. Local measurements of snow accumulation were collected with Airborne Laser Scanning
(ALS) at the Wannengrat area (Davos, Switzerland) for the winters 2007/08 and 2008/09. The spatial
distribution of snow accumulation exhibits a strong inter-annual consistency that can be generalized
over the winters in the area. This unique configuration makes the comparison of the variability in
snowfall (as seen by the radar) and in snow accumulation (from laser scans) possible over the diverse
winter seasons.
The spatial variability, quantified by means of the variogram, is shown to be larger in snow
accumulation than in snowfall (at the seasonal scale). This indicates that other factors (like wind and
turbulence taking place close to the ground) induced by small-scale topographic features govern the
snow deposition and accumulation at the ground level in mountainous areas. Further investigation of
this question is done by dividing the radar coverage into two disjoint domains at different elevations,
roughness, and proximity to the ground. The variability of snowfall appears consistently larger in the
vicinity of the ridge than far from the ground, which confirms the influence of the rugged topography on
snowfall. In addition, small-scale turbulence is stronger close to the surface where winds are in direct
contact with the terrain, as observed from normalized histograms of Doppler spectral width. Finally,
normalized variograms of Doppler radial velocity showed a more organized structure at higher
elevations. This corroborates the important role of small-scale topography in spatial distribution of
snowfall/snow accumulation.
Page | 11
842
Implementation and evaluation of prognostic representations of the optical
diameter of snow in the detailed snowpack model SURFEX/ISBA-Crocus
1
1
1
2
3
Carlo Carmagnola , Samuel Morin , Matthieu Lafaysse , Florent Domine , Ghislain Picard , Laurent
3
Arnaud
1
2
Météo-France - CNRS, CNRM - GAME, CEN, St Martin d'Hères, France, Takuvik Joint International
3
Laboratory, CNRS and Université Laval, Québec, Canada, CNRS - Université Joseph Fourier
Grenoble, LGGE, Grenoble, France
Few snowpack models incorporate an explicit representation of metamorphism processes. In the
SURFEX/ISBA-Crocus multi-layer snow model, snow metamorphism is implemented in a
phenomenological way, through a set of equations describing the evolution rate of the grain
properties. Snow grains are characterized by their size and by semi-empirical shape variables,
dendricity and sphericity, which cannot be measured easily in the field or linked to other relevant snow
properties. The optical diameter (which is, in contrast, a well-defined variable representing the
geometric characteristics of a porous medium) is then derived from those quantities in order to
compute the NIR albedo of snow.
Here we introduce an alternative approach, in which snow metamorphism within Crocus model is now
described by equations formulated in terms of the rate of change of two state variables, sphericity and
optical diameter. In other words, we replaced two of the primary Crocus parameters (dendricity and
size) with optical diameter, turning the latter into a prognostic variable in the code. This new
formulation makes it easier to implement different parameterisations of the rate of increase of optical
diameter, in addition to the reformulation in terms of sphericity and optical diameter of the current
metamorphism laws.
These parameterizations were then evaluated by comparing them to field measurements. Two
instruments which retrieve optical diameter from infrared reflectance measurements at 1310 nm,
DUFISSS and ASSSAP, were used in May and June 2011 at Summit Camp (Greenland) and during
the 2011/12 winter season at Col de Porte (French Alps). During these field campaigns, data were
acquired with high vertical resolution (about 1 cm), allowing to test the accuracy of the different dry
metamorphism formulations.
Page | 12
A6.1a - Advances in ice sheet modelling
08.07.2013 10:15-11:45, Forum
705
Impact of difference in numerics and boundary conditions on uncertainties in
ice-sheet simulation
1
2
1
Fuyuki Saito , Ayako Abe-Ouchi , Kunio Takahashi
1
2
JAMSTEC, Yokohama, Japan, AORI, University of Tokyo, Kashiwa, Chiba, Japan
There have been a number of ice-sheet modeling studies including intercomparison. It is important to
study how the simulation is influenced by difference in several aspects (model, forcings, etc) to show
what is robust and what is not.
In this presentation we show the uncertainties in ice-sheet simulation in terms of (minor) pure
numerics as well as (major) boundary conditions to drive the experiment. The reason why we have
various results is partly because the numerical
models can differ in many aspects, such as discretization methods, the derivation routes from the
governing equations to the actual equations represented in the numerical models, and so on.
Saito (2012) show, however, even if these aspects are the same, different results can be yielded by
different handling of numerical operations and numbers, due to the finite accuracy of computing
machines, using the ISMIP-HEINO (Calov et al 2010) exercises.
We show even small perturbation can change the total behavior dramatically.
Moreover, there are much possibility how to compute the input of ice-sheet models. Many studies
apply a combination of reference-anomaly method for surface temperature and a parameterization
method to compute surface mass balance.
We show sensitivity of Greenland ice sheet under spatially uniform warming condition and how the
response is influenced by difference in the way to compute surface mass balance.
Page | 13
1022
Verification methods for planview marine ice sheet models and requirements
for grounding line migration
1
1
2
2
2
Frank Pattyn , Laura Perichon , Gael Durand , Lionel Favier , Olivier Gagliardini , Richard C.A.
3
4
Hindmarsh , Thomas Zwinger
1
2
Laboratoire de Glaciologie, Université Libre de Bruxelles, Brussels, Belgium, Laboratoire de
3
Glaciologie et Géophysique de l'Environnement, Grenoble, France, British Antarctic Survey,
4
Cambridge, United Kingdom, CSC - IT Center for Science Ltd., Espoo, Finland
Predictions of marine ice-sheet behaviour require models able to simulate grounding line migration.
We present results of an intercomparison experiment for plan-view marine ice-sheet models.
Verification is effected by comparison with approximate analytical solutions for flux across the
grounding line using simplified geometrical configurations (no lateral variations, no buttressing effects
from lateral drag). A unique steady state grounding line position exists for ice sheets on a downward
sloping bed under those simplified conditions. Perturbation experiments specifying spatial variation in
basal sliding parameters permitted the evolution of curved grounding lines, generating buttressing
effects. The experiments showed regions of compression and extensional flow across the grounding
line, thereby invalidating the boundary layer theory. Models based on the shallow ice approximation,
which neither resolve membrane stresses, nor reproduce the approximate analytical results unless
appropriate parameterizations for ice flux are imposed at the grounding line, are invalid. Steady-state
grounding line positions were found to be dependent on the level of physical model approximation.
Models that only include membrane stresses result in ice sheets with a larger span than those that
also incorporate vertical shearing at the grounding line, such as higher-order and full-Stokes models.
From a numerical perspective, resolving grounding lines requires a sufficiently small grid size (< 500
m), or sub-grid interpolation of the grounding line. The latter still requires nominal grid sizes of < 5 km.
For larger grid spacings, appropriate parameterizations for ice flux may be imposed at the grounding
line, but the short-time transient behaviour is then incorrect and different from models that do not
incorporate grounding line parameterizations. The numerical error associated with predicting
grounding line motion can be reduced significantly below the errors associated with parameter
ignorance and uncertainties in future scenarios.
Page | 14
919
The influence of shear bands on the grounding line retreat in Pine Island
Glacier
1
1
2
1
3
Lionel Favier , Gaël Durand , Stephen Cornford , Olivier Gagliardini , Thomas Zwinger
1
2
3
LGGE (CNRS/UJF), St Martin d'heres, France, University of Bristol, Bristol, United Kingdom, CSC,
Espoo, Finland
Pine Island Glacier (PIG), West Antarctica, is known as the weak underbelly of the West Antarctic Ice
Sheet. During the last 30 years, it has undergone a dramatic acceleration along with a retreat of its
grounding line. The main ice stream draining PIG is laterally bounded by two bands of damaged ice.
We may presume that these shear bands could play a key role in the dynamics of the grounding line.
A usual approach is generally to infer the viscosity from surface velocity using data assimilation
methods. However, in that case the inverse problem is under-constrained when inversion of basal
drag and viscosity are coupled, i.e. various sets of basal drag and viscosity patterns can lead to a
similar match between modeled and observed surface velocities. Here, we follow a simpler approach
and perform a sensitivity study on the shear bands effective viscosity, and investigate its
consequences in terms of ice dynamics and discharge. The areas of fractured ice at PIG are located
using a recent satellite images and viscosity in identified sheared areas is decreased. Using two
different higher-order models (Elmer/Ice and BISICLES), we investigate the influence of the shear
bands´ damage on the grounding line dynamics. We show that the presence of the shear bands
substantially modulates the buttressing state in the ice shelf, i.e. the amount of back stress transmitted
to the grounding line. The discharge of grounded ice in response to an oceanic perturbation is thus
strongly influenced by the estimation of the ice shelf rheology. This suggests that projections of PIG
behavior will have to carefully evaluate both the spatial and temporal ice-shelf rheology and its
evolution.
Page | 15
943
Numerical simulations of ice rises under rising sea level - a finite element
contact pairs approach
1,2
3
2
Martin Rückamp , Angelika Humbert , Ralf Müller
1
2
University of Hamburg, Hamburg, Germany, Mechanical and Process Engineering, University of
3
Kaiserslautern, Kaiserslautern, Germany, Alfred Wegener Institute for Polar and Marine Research,
Bremerhaven, Germany
Ice rises play a key role in the stability of ice shelves and often determine the shape of the calving
front. Located in the interior of an ice shelf, they cause inhomogeneities, which split the flow in
different units or initiate fracture fields that pre-condition the ice shelf for failure. Sea level changes or
changes in the mass balance may cause the ice shelf to become afloat.
A projection of grounding line (boundary between grounded and floating ice) migration requires a
robust numerical ice-sheet model. A crucial finding about grounding line dynamics is the strong
dependency on the horizontal grid size at the grounding line. The dynamical processes incorporating
all stress components need to be resolved on a horizontal scale in the order of the local ice thickness
and below. For this reason a finite element full-Stokes model allowing for higher grid resolution in the
vicinity of the grounding line was developed. Instead of using a floatation criterion to distinguish
between floating and grounded ice parts, it solves the evolution equations of the ice upper and lower
surfaces. The grounding line position in the new model is determined by solving the contact problem
between the ice and the bedrock. The method is implemented in the commercial finite element
package: COMSOL Multiphysics.
A flowline case of the flow-model is applied to the Fimbulisen where several ice rises are wellsurveyed. The studies are focused on the dynamic response of the ice shelf and the evolution under
changing boundary conditions as sea level changes or/and mass-balance.
Page | 16
1137
A simple parameterisation of ice shelf basal melting and its implementation in
the ice sheet model SICOPOLIS
1
2
1
Tatsuru Sato , Ben Galton-Fenzi , Ralf Greve
1
2
Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan, Antarctic Climate &
Ecosystems Cooperative Research Centre, Hobart, Australia
Long-term simulations of the Antarctic ice sheet require that ice shelf basal melting is parameterised.
This is primarily because integrating coupled ocean and ice sheet models for long time periods at high
resolution is not achievable within a reasonable time using present-day computers. Using
paramterised external forcing also allows to examine changes in the Antarctic ice sheet to specified
forcing changes. Here we describe a simple paramterisation that calculates the basal melting of ice
shelves as a function of both the depth of ice below mean sea level and far-field ocean temperatures.
The parameterisation can be tuned differently for various Antarctic sectors in order to achieve
reasonable agreement with the modern spatial distribution of ice shelf basal melting. It is then
implemented in the Antarctica module of the dynamic/thermodynamic, large-scale ice sheet model
SICOPOLIS (sicopolis.greveweb.net). We discuss paleoclimatic runs over the most recent
glacial/interglacial cycle as well as future climate runs over the next centuries with various climatic and
oceanic forcings. The model will help provide new insight into estimating both past and future
contributions of the ice sheet to both sea level rise and the heat budgets of the ocean.
Page | 17
C2.2 - Quantifying solid precipitation: measuring and modelling challenges
08.07.2013 10:15-11:45, Studio
262
Ice in clouds and precipitation: addressing and solving measurement problems
workshop summary
1
Darrel Baumgardner
1
Research and Development, Droplet Measurement Technologies, Boulder, United States
Significant progress has been made in the last thirty years towards understanding the formation and
evolution of clouds and their impact on weather and climate; however, serious gaps remain, many of
which are associated with uncertainties and limitations related to the measurement of ice particle
properties in clouds and precipitation. Evaluating quantitatively the many effects of cloud processes on
weather and climate is hindered by the lack of adequate sensors for 1) identifying the primary modes
of ice initiation and the composition of ice nuclei, 2) discriminating liquid water from ice, 3) segregating
crystal shapes by size, 4) determining the chemistry of aerosol and cloud hydrometeors, 5) analyzing
the optical properties of single and ensembles of cloud particles, 6) determining the fall velocities of ice
crystals, 7) measuring the intensity, water content and size distribution of precipitating and nonprecipitating particles and 8) measuring the small-scale surface characteristics of ice crystals.
A workshop was held July 5-6, 2013 at the ETH, Zurich, Switzerland to address the primary issues
related to measuring the properties of ice in clouds and precipitation. In particular, working groups
were formed prior to the meeting to gather information and prepare presentations prior to the meeting
on the topics of 1) science related to understanding ice in clouds and precipitation and the need for
measurements, 2) missing or scarcity of measurements, 3) data quality and analysis and 4) emerging
technologies. The working groups were co-led by experts in remote sensing and in-situ measurement
systems and participants were from both the remote sensing and in situ measurement communities.
This presentation summarizes the findings and recommendations from the workshop.
Page | 18
150
Detecting precipitation events in Antarctica by spatial radar and in situ
measurements
1,2
2
3
4
1,4
Cyril Palerme , Christophe Genthon , Jennifer Kay , Florence Naaim-Bouvet , Charles Amory
1
2
3
LGGE, Universités de Grenoble, Grenoble, France, LGGE, CNRS, Grenoble, France, National
4
Center For Atmospheric Research (NCAR), Boulder, United States, Institut National de Recherche en
Sciences et Technologies pour l'Environnement et l'Agriculture (IRSTEA), Grenoble, France
The mass balance of the Antarctic ice sheet is a key parameter of sea level rise. One of the
consequences of global warming should be an increase of precipitation and thus of accumulation in
Antarctica. This should moderate sea-level rise.
th
In the last IPCC report (4 ), the Coupled Model Intercomparison Project (CMIP) predict a precipitation
increase between 0 and 50% in Antarctica for the end of the century. Nevertheless, in situ data are not
reliable due to difficulties in distinguishing between blowing snow and precipitation.
Thanks to spatial radar measurements, it is currently possible to detect snowfall in the peripheral part
of the ice sheet which represent three quarter of precipitation in Antarctica.
Moreover, a new project on an instrumented mast of 73 meters high will be tested from January 2013
in order to obtain in situ data. It could provide a new dataset to validate remote sensing results.
th
We are working to assess model ability of the 5 IPCC report to reproduce precipitation by comparing
their outputs with our observations. Large differences are expected between the various models. We
hope that this work will help assess which models are the most reliable in their predictions for the next
century.
Page | 19
1238
Comparisons of solid precipitation measurements using traditional snow
gauges, exotic optical probes and C band radar in Southern Ontario, Canada
1
1
2
1
1
1
Faisal Boudala , Paul Joe , Rodica Nitu , George A. Isaac , Dave Hudak , Suduesh Boodoo , Kai
2
Wong
1
Cloud Physics and Severe Weather Research Section, Environment Canada, Toronto, Canada,
2
Meteorological Service of Canada, Environment Canada, Toronto, Canada
Accurate measurement of solid precipitation is crucial for understanding the hydrological cycle,
development of climate models, and satellite and radar remote sensing algorithms. Solid precipitation
is traditionally measured using a weighting gauge which is an open container on the ground that can
collect falling hydrometeors. In practice, however, measuring solid precipitation is hard mainly due to
wind effects. Precipitation can be also measured using instruments such as distrometers, but they rely
heavily on internal algorithms that employ some crude assumptions about properties of falling snow
particles and hence they need to be calibrated using weighting gauges. Currently there are major
efforts being made to address the measurement uncertainty of solid precipitation. Two good examples
are: The Global Precipitation Mission Cold-season Precipitation Experiment (GCPEX) that was
conducted in the winter of 2011 and the World Meteorological Organization (WMO) Solid Precipitation
Intercomparison Experiment (SPICE) project that is being conducted in the next few years starting with
the pre-SPICE project which was conducted during winter 2011-2012. To support these efforts, a
number of instruments have been installed at the Centre for Atmospheric Research Experiments
(CARE) site located in Southern Ontario, Canada. These include a FD12P, PWD22, FS11P, Hotplate,
Parsivel and vertically pointing radar. There are also existing instruments at this site including Pluvio
and Geonor gauges, and the WMO Double Fence Intercomparison Reference (DFIR) shield system.
Based on observations made during the winters of 2011-2012 and 2012-2013, the solid precipitation
measurements from the instruments listed above and C band Dual-pol radar will be compared and the
preliminary results will be presented.
Page | 20
1231
Solid precipitation measurements in Arctic regions and its effect on Arctic heat
budget
1
2
3
Ismail Gultepe , Thomas Kuhn , Martin Stuefer
1
2
Cloud Physics and Severe Weather Section, Environment Canada, Toronto, Canada, Lulea
3
University of Technology, Kiruna, Sweden, University of Alaska, Fairbanks, United States
The goals of this work are to emphasize: 1) the uncertainty in solid precipitation measurements, 2) the
precipitation variability over a given time and space, and 3) the effects of shape and density of ice
crystals on precipitation measurements. Solid precipitation measurements were collected using
weighing gauges, optical instruments, and capacitor sensors over the Arctic regions during the Fog
Remote Sensing And Modeling-Ice Fog (FRAM-IF) and the Satellite Applications for Arctic Weather
and SAR (Search And Rescue) Operations (SAAWSO) projects. These projects took place over
Yellowknife, NWT, and St. John's, NFL, Canada during the winters of 2010-2011 and 2012-2013,
respectively. In this presentation, solid precipitation observations at the surface from these two
projects will be summarized for various dynamical and thermodynamical conditions.
The following results are obtained from the analysis of observations: a) Snow measurements were
impossible with or without a wind shield over an open field when blowing snow conditions exist. b) The
strong 3D winds caused to a large uncertainty in precipitation rate measurements. c) Light
-1
precipitation rate (< 0.5 mm hr ) at the cold temperatures was a strong function of relative humidity
-1
with respect to ice, and particle shape and density. d) Light precipitation rate (< 0.5 mm hr ) was not
measured by weighing gauges accurately. Thus, the uncertainty in the solid precipitation observations
can be as large as 50-100% over the continental and maritime Arctic regions and its measurements
depend on precipitation sensor type, dynamics and thermodynamics of the boundary layer,
geographical area, and cloud forming layers above. Because of this large measurement uncertainty,
estimation of the Arctic heat and moisture budget terms may include large uncertainties; therefore, it is
concluded that improvements for solid precipitation measurements are required.
Page | 21
389
Ground-based observation of liquid-water fraction of melting snowflakes
1
2
2
2
2
Ryohei Misumi , Hiroki Motoyoshi , Satoru Yamaguchi , Sento Nakai , Masaaki Ishizaka , Yasushi
3
Fujiyoshi
1
2
National Research Institute for Earth Science and Disaster Prevention, Tsukuba, Japan, Snow and
Ice Research Center, National Research Institute for Earth Science and Disaster Prevention,
3
Nagaoka, Japan, Institute for Low Temperature Science, Hokkaido University, Sapporo, Japan
Liquid-water fraction of individual snowflakes (f) is an important parameter for calculating radar
reflectivity in melting layers from numerical-model outputs. However, the measurement technique of f
has not been established. We conducted ground-based observation of f at Nagaoka, Japan, using
dye-treated filter papers kept at 0 °C by a cooling unit. The observed values were calibrated using
polyurethane flakes in which known amount of liquid water was soaked. Based on the measurement of
6,179 particles with 43 sheets of filter papers, an empirical relationship between the contribution rate
of liquid water to precipitation intensity (FL) and meteorological elements at the ground, and that
between f and melted diameter were obtained. A numerical simulation of melting snowflakes that
assumed spherical shapes for particles well reproduced the size dependence of f, while there were
some disagreements for the relation between FL and temperature.
Page | 22
B3.2a - Dynamics of mountain weather and climate
08.07.2013 10:15-11:45, Wisshorn
541
Scaling the quasi-steady along-valley wind
1
2
Jürg Schmidli , Richard Rotunno
1
2
Institute for Atmospheric and Climate Science, ETH Zürich, Zürich, Switzerland, National Center For
Atmospheric Research (NCAR), Boulder, United States
The quasi-steady-state limit of the diurnal valley wind system is investigated over idealized threedimensional topography. Although this limit is rarely attained in reality due to ever-changing forcings,
the investigation of this limit can provide valuable insight, in particular on the mass and heat fluxes
associate with the along-valley wind. We derive a scaling relation for the quasi-steady-state alongvalley mass flux as a function of valley geometry, valley size, atmospheric stratification, and surface
sensible heat flux forcing. The scaling relation is tested by comparison with the mass flux diagnosed
from large-eddy and mesoscale simulations of the valley wind system. Good agreement is found. The
results also provide insight into the relation between surface friction and the strength of the alongvalley pressure gradient.
Page | 23
191
Turbulence averaging scale for bora flows at the NE Adriatic coast
1
2
1
Zeljko Vecenaj , Danijel Belusic , Branko Grisogono
1
2
Department of Geophysics, University of Zagreb, Faculty of Science, Zagreb, Croatia, School of
Mathematical Sciences, Monash University, Melbourne, Australia
At the Eastern Adriatic coast often blows a downslope windstorm called bora. It flows from the northeastern (NE) quadrant, and it occurs most frequently during winter seasons. Bora mean wind speed
-1
-1
can surpass 20 m s and due to its gustiness it occasionally reaches speeds greater than 60 m s .
During such events, the turbulence is strongly developed in the lee of the mountains; moreover, submesocale and turbulent structures are additionally complicated at the middle of the NE Adriatic coast
due to the upwind and surrounding mountains.
In order to investigate turbulence, a suitable time/space averaging scale has to be deployed in order to
define turbulent perturbations; these quantities later on characterize turbulent kinetic energy,
gustiness, etc. This study addresses the turbulence averaging scale for bora events recorded by the
Gill WindMaster ultrasonic anemometers in the town of Senj (44.99°N, 14.90°E, 2 m above MSL), 13
m above the ground, in the period from March 2004 to June 2006, and Vratnik Pass (44.98°N,
14.98°E, 700 m above MSL), 10 m above the ground in the period from October 2004 to September
2005. Bora events extracted from these periods at both sites are categorized by duration and mean
wind speed, which can provide some specific conclusions about the turbulence averaging scale for
bora flows.
Page | 24
567
Two types of westerly tip jets near Greenland
1
1
2
3
Qi Kong , Thomas Spengler , Melvyn Shapiro , Andreas Dörnbrack
1
2
University of Bergen, Bergen, Norway, NOAA Environmental Technology Lab. and National Centre
3
for Atmos. Research, Boulder, United States, Institut für Physik der Atmosphäre, DLR
Oberpfaffenhofen, Wessling, Germany
The westerly Greenland tip jet is a narrow and intense low-level jet in the lee of Cape Farewell. It
mainly occurs during wintertime and has strong inter-annual variability. In the present study, we use
airborne in-situ and remote-sensing observations and high-resolution numerical simulations with WRF
to study two westerly Greenland tip jet cases. The first case occurred 24 November 2003, where the
airborne observations reveal new insights into the complex structure of the Greenland tip jet event,
featuring two jet branches and a wake in between. One of the jets is located at the southeast of Cape
Farewell, which is the Greenland tip jet. The other is located to the north and is connected to a
downslope wind-storm. These jets are well reproduced by the model simulation, but their magnitude is
-1
slightly overestimated. The maximum wind of the Greenland tip jet of about 32 ms occurs at around
850 hPa. The results show that the tip jet is associated with strong mountain gravity wave activity,
where the wave energy radiates upwards into the stratosphere. In contrast to the case observed in
2003, we also present another different tip jet case that occurred 18 February 1997. Here, the tip jet
development is concurrent with strong frontogenesis which parallels to the tip jet and is situated along
the northern boundary of tip jet. The baroclinic zone tilts southwards. In this case, the gravity waves
are trapped with the energy channelled downstream and the tip jet is relatively long and intense. We
compare the two different types of tip jets, which we refer to as the barotropic tip jet (case 2003) and
the baroclinic tip jet (case 1997) and discuss the significantly differing dynamical mechanisms of these
two types of tip jets.
Page | 25
392
Semibalance model in terrain-following coordinates
1
Jie Cao
1
Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), Beijing, China
By partitioning the hydrostatically-balanced flow into a nonlinearly-balanced primary-flow part and a
remaining secondary-flow part and then truncating the secondary-flow vorticity advection and
stretching-tilting terms in the vector vorticity equation, the semibalance model (SBM) of Xu (1994) in
pseudoheight-coordinates is re-derived in terrain-following pressure coordinates, i.e, WRF's < yeta>coordinates (Skamarock et al., 2008). The involved truncation is topologically the same as that in
pseudoheight-coordinates but the truncated terms in < yeta>-coordinates are not equivalent to those
in pseudoheight-coordinates. As its potential vorticity (PV) is conserved and invertible, the re-derived
SBM is suitable for studying balanced dynamics via “PV-thinking” in real weather events, such as
slowly-varying vortices and curved fronts in which the primary-flow velocity and secondary-flow
vorticity are nearly parallel in < yeta>-coordinates.
Theoretical derivation and diagnostic analyses are presented to describe qualitatively and
quantitatively the ability of this new dynamic model in extracting the balanced part from initial modelsimulated datasets in terrain-following coordinates. This study may benefits not only in data
assimilation for model developments, but also in better understanding synoptic and meso-scale
processes with full use of abundant model-simulated datasets in terrain-following coordinates.
Page | 26
249
Some current and future research on bora wind
Branko Grisogono , Željko Večenaj , Josipa Milovac , Petra Lepri , Goran Gašparac , Kristian
3
5
Horvath , Hrvoje Kozmar
1
2
University of Zagreb, Faculty of Science, Zagreb, Croatia, Institute of Physics and Meteorology,
3
University of Hohenheim, Stuttgart, Germany, Meteorological and Hydrological Service of Croatia,
4
5
Zagreb, Croatia, Gekom, Zagreb, Croatia, Faculty of Mechanical Engineering and Naval
Architecture, University of Zagreb, Zagreb, Croatia
1
1
2
3
4
Bora is a typical gusty wind which blows at the eastern Adriatic coast from the NE quadrant with
-1
-1
sustained speeds between 5-20 ms , its gusts surpassing 50-70 ms (corresponding to downslope
windstorms with hurricane speeds) in the lee of the mountains. Similar bora-like flows occur elsewhere
in mountainous areas where flow transcriticality (regarding “vertical” Froude number, or its inverse,
dimensionless mountain height) is the dominant flow property. On the finer mesoscale, the bora jet
and wake pattern relates to the mountain pass and top distribution.
Significant current and future efforts in studying bora gradually moves toward progressively smaller
spatio-temporal scales, i.e., toward micrometeorology and bora turbulence. One feature of bora
turbulence is its anisotropy, i.e., the velocity component variance aspect ratio. The enhanced bora
anisotropy might explain barely adequate experimental, otherwise fine dimensional scaling between
bora turbulent kinetic energy, its dissipation and integral length-scale. Next, due to increased
application needs, wind-energy and engineering (in addition to air-pollution and health) communities
demand simple and robust wind speed estimates for the bora surface layer. We deploy Prandtl scaling
α
for two-level bora wind speed and the corresponding heights, u1/u2 = (z1/z2) , where typically 0.15 ≤ α
≤ 0.4; appropriate averaging time is essential for obtaining suitable α value(s). Finally, we introduce a
generalized mixing length-scale for all nonnegative gradient Richardson number values in WRF
mesoscale model in order to better simulate various types of bora flows.
Page | 27
A3.1a - ENSO and decadal variability under climate change
08.07.2013 10:15-11:45, Schwarzhorn
733
El Niño duality and sensitivity
1
Fei-Fe Jin
1
Department of Meteorology, University of Hawaii at Manoa, Honolulu, United States
Decades of observational and theoretical studies have portrayed the El Niño phenomenon as one
phase of a natural oscillatory mode sprang from the instability of the tropical Pacific climate
background state owing to unstable ocean-atmosphere interactions. The basic dynamics of the mode
is largely understood by invoking either one of the two thought to be parallel but different paradigms:
the delayed-oscillator and recharge-oscillator models. However, major issues still remain to be
resolved. For example, there are evidences pointing to significant different behaviors of ENSO, such
as the so-called warm-pool and cold-tongue types of ENSO. Then, what is the dynamic base for this
kind of ENSO Duality? How the two ENSO paradigms can be reconciled to explain the different
behaviors of ENSO? New theoretical results are present to support a new hypothesis for El Niño
Duality: its variations in the modern time, such as its different patterns and frequencies, are linked to
not one but two similar but distinct leading oscillatory modes from the same instability. The dichotomy
of delayed-oscillator and recharge-oscillator paradigms for El Niño thus is united with the two
oscillators capturing the different physical mechanisms of these two modes. ENSO Duality may thus
be intrinsic, which makes ENSO sensitive to tropical climate state changes.
Page | 28
267
Similarities between precursors for El Niño events and initial errors in the
predictions and implications in targeted observation
1
2
3
3
1
Mu Mu , Yanshan Yu , Wansuo Duan , Hui Xu , Tingting Gong
1
2
Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China, School of Mathematical
3
Sciences, Monash University, Melbourne, Australia, LASG, Institute of Atmospheric Physics, Chinese
Academy of Sciences, Beijing, China
With the Zebiak-Cane model, the relationship between the optimal precursors (OPRs) for El Niño
events and the optimally growing initial errors (OGEs) in El Niño predictions is investigated by the
approach of conditional nonlinear optimal perturbation (CNOP). The computed OPRs for El Niño
events in SSTA have a dipole pattern in the equatorial central and eastern Pacific, plus positive
thermocline depth anomalies in the equatorial Pacific. Based on the El Niño events triggered by the
obtained OPRs, the OGEs, which cause the largest prediction errors, are found to share great
similarities with OPRs in terms of localization and spatial structure of the initial SSTA dipole and the
uniform thermocline. The resemblances are possibly caused by the same mechanism of the Bjerknes
positive feedback.
Numerical experiments show that the location and spatial pattern of the initial errors play important
roles in the prediction error evolution. Only when initial errors with a dipole are located in the equatorial
central and eastern Pacific, rather than other regions, do they evolve into non-negligible prediction
errors. Random error, even with same magnitude as the OGEs but without dipole, does not evolve
significantly over time. Consequently, the magnitude of prediction error depends on the combined
effects of the location and spatial pattern of the initial error.
Based on the findings of the similarities and the above numerical experiments ,we further design
observation system simulation experiments (OSSE) .It is found that there exist a sensitive area in the
equatorial central and eastern Pacific for El Niño precursors development and initial error growth in El
Niño prediction. If additional observation instruments are deployed to targeted observations with
limited coverage, they should preferentially be deployed in sensitive area to better detect the signals
for El Niño events and reduce the initial errors so as to improve the forecast skill.
Page | 29
447
Tropical Atlantic influences on ENSO variability
1
2
3
4
Jong-Seong Kug , Yoo-Geun Ham , Jong-Yeon Park , Fei-Fei Jin
1
2
3
KIOST, Seoul, Korea, Republic of, NASA/GSFC, Greenbelt, United States, KIOST, ansan, Korea,
4
Republic of, Univ. Hawaii, Honolulu, United States
El Niño events, the warm phase of the El Niño/Southern Oscillation (ENSO), are known to affect other
tropical ocean basins through teleconnections. On the other hand, there are mounting evidences that
temperature variability in the Atlantic Ocean may also influence ENSO variability. Here we use
reanalysis data and general circulation models to show that sea surface temperature (SST) anomalies
in the North Tropical Atlantic during the boreal spring can serve as a trigger for ENSO events. We
identify a subtropical teleconnection in which North Tropical Atlantic warming can induce a low-level
cyclonic atmospheric flow over the eastern Pacific that in turn produces a low-level anticyclonic flow
over the western Pacific during the following months, cooling the equatorial Pacific through the
easterlies over the equatorial western Pacific. Especially, this process seems to favor the development
of a warm pool El Niño event with a centre of action located in the central Pacific, rather than the
canonical event. We suggest that the identification of temperature anomalies in the North Tropical
Atlantic could help to forecast the development of different types of El Niño events.
Page | 30
779
Recharge oscillator mechanism in warm-pool ENSO
1
2
Hongli Ren , Fei-Fei Jin
1
2
LCS, National Climate Center, China Meteorological Administration, Beijing, China, Meteorology
Dept, University of Hawaii, Honolulu, United States
El Niño and Southern Oscillation (ENSO) in recent decades tends to behave arguably in two different
types. One is the canonical cold-tongue (CT) -type ENSO with major sea surface temperature
anomalies (SSTA) positioned over the eastern Pacific. The other is a warm-pool (WP) -type ENSO
with SSTA centered in the central Pacific by the WP edge. In this study, we examine the basic
features and main feedback processes of these two types of ENSO. It is shown that the interannual
variability of upper-ocean heat content exhibits recharge-discharge processes throughout the life
cycles of both the CT and WP types of ENSO. Through heat budget analyses focused on the
interannual variability, we further demonstrate that the thermocline feedback plays a dominant role in
contributing to the growth and phase transitions of the both types of ENSO, whereas the zonal
advective feedback contributes mainly to their phase transitions. The westward shift of the SSTA
center of the WP ENSO and the presence of significant surface easterly wind anomalies over the far
eastern equatorial Pacific during its mature warm phase are the two main factors that lead to a
reduced positive feedback for its eastern-Pacific SSTA. Nevertheless, both the WP and CT ENSO can
be understood to a large extent by the recharge oscillator mechanism.
Page | 31
355
A role of the Eurasian snow on the 1-year lagged NAO-ENSO relationship
1,2
3
4
3,4
Tetsu Nakamura , Masayuki Hara , Miki Oshika , Yoshihiro Tachibana
1
2
Arctic Environment Research Center, National Institute of Polar Research, Tokyo, Japan, Hokkaido
3
University, Sapporo, Japan, Japan Agency for Marine-Earth Science and Technology, Yokohama,
4
Japan, Mie University, Tsu, Japan
One year lagged relationship between North Atlantic Oscillation (NAO) and El Niño/Southern
Oscillation (ENSO) was examined by the multi model ensemble analysis using CMIP-3 models. An
index, named the coherency index which indicates the coherency between NAO and ENSO in each
model, was newly developed and used as a weight of the model. Weighted multi model ensemble
st
mean of the regressed field on the 1 mode score of singular value decomposition between surface
pressure field in the North Atlantic region (NAO field) and sea surface temperature field in the
equatorial Pacific region (ENSO field) was explored. As a result, when the wintertime NAO is in the
negative (positive) phase, the anomalous atmospheric circulation associated with the large (less)
Eurasian snow anomaly intensify (weaken) the Asian cold surge and the westerly wind burst (WWB) in
the warm pool region, initiating El Niño. A sensitivity experiment using idealized dry general circulation
model exhibited that the atmospheric response to the anomalous cooling near surface associated with
the anomalous Eurasian snow amount induces higher surface pressure near the Tibetan plateau and
thus intensifies the Asian cold surge and WWB. Linear regression analyses applied to the reanalysis
data strongly supported the model results. Therefore, our results suggest the possible influence of
NAO on the initiating El Niño and the process through the Eurasian snow anomalies associated with
NAO phase.
Page | 32
B1.3 - Applications to weather and climate prediction
08.07.2013 10:15-11:45, Seehorn
865
Dynamic probabilities, mature probabilities, and the links between data
assimilation and ensemble forecasting in actual decision support
1,2
Leonard Smith
1
2
London School of Economics, London, United Kingdom, Pembroke College, Oxford, United Kingdom
Given a perfect model, the aim of data assimilation is well-defined and generally widely-agreed. While
finite computational resources will preclude a perfect probability forecast, an accountable forecast can
be achieved. An accountable forecast suffers only from the sampling uncertainties unavoidable in any
finite ensemble, and converges toward a perfect probability forecast as the ensemble size increases to
infinity, yielding what I.J. Good termed "dynamic probability". In this case, the aims of data assimilation
can be cast in a fully Bayesian framework, while means of achieving useful probabilistic forecasts may
follow a different path and deliver something less than a full probability distribution for the forecast
target. These insights from the Bayesian Way can be extended to the case of uncertain parameter
values, but not to the case of structural model error: error in the mathematical form of the model
equations such that the model class in-hand does not admit a model consistent with the mechanism
generating the observations. In this case, the aim of data assimilation will vary with the forecast target
and lead-time; nevertheless there are more effective and less effective approaches to ensemble
formation and forecasting, and the two become perhaps more deeply intertwined. While the Bayesian
Way may still guide our thinking, the relevance of the probability calculus (and thus of Bayes'
Theorem) is no longer assured. Indeed the very notion of "the distribution of truth" can prove worse
than a distraction.
Ensemble climate forecasts require consideration of "mature probabilities" and while an estimate of
the inherent forecast uncertainty of future states of the atmosphere remains the aim, it is no longer at
all clear that this inherent uncertainty is best communicated or explored when cast as a probability.
Both robust conclusions and more speculative suggestions for decision support outside the perfect
model scenario will be presented.
Page | 33
481
MOGREPS-UK - development of a convective-scale ensemble forecast system
for the UK
1
2
1
1
2
Richard Swinbank , Nigel Roberts , Warren Tennant , Christine Johnson , Aurore Porson , Anne
1
McCabe
1
2
Met Office, Exeter, United Kingdom, Met Office, Reading, United Kingdom
The latest addition to the Met Office Global and Regional Ensemble Prediction System (MOGREPS)
family is a convective-scale (2.2 km) system for the UK, which is based on the UK variable-resolution
model (UKV). MOGREPS-UK was launched in summer 2012, as a major part of the Met Office
Olympic showcase to support the London 2012 games.
MOGREPS-UK is now running routinely, with a 12-member ensemble being run four times a day. In its
initial implementation, initial and boundary conditions were taken from the regional 18 km ensemble.
From early in 2013, MOGREPS-UK is directly nested in a (32 km) global ensemble. It is currently a
downscaling ensemble - driven entirely by the coarser resolution ensemble in which it is nested.
The talk will include results illustrating the performance of MOGREPS-UK in selected case studies,
including high risk events such as intense rainfall and low visibility. MOGREPS-UK forecasts will also
be compared with the deterministic UKV forecasts and other ensemble predictions.
Several options for developing MOGREPS-UK are currently under investigation, including use of the
UKV analysis for initial conditions and the introduction of stochastic physics schemes. Some early
results from these studies will be presented.
Page | 34
778
The impact of initial condition perturbations in a convection-permitting EPS
under different synoptic-scale forcing
1
1
1
2
Christian Keil , Christian Kühnlein , George C. Craig , Christoph Gebhardt
1
2
LMU München, München, Germany, Deutscher Wetterdienst, Offenbach, Germany
The convection-permitting ensemble prediction system COSMO-DE-EPS has been operational at
Deutscher Wetterdienst since May 2012. The individual ensemble members are created by perturbing
the lateral boundary conditions of the limited-area model to account for synoptic-scale uncertainty, and
tunable parameters in selected physics parameterisation schemes aiming at smaller-scale uncertainty.
In addition, initial condition perturbations based on downscaling from a multi-model global EPS have
been incorporated.
Here, we investigate the influence of the downscaled initial condition perturbations for the short-range
ensemble forecasts of convective precipitation at convection-permitting resolution. The COSMO-DEEPS with lateral boundary condition perturbations, physics perturbations, and initial condition
perturbations is compared to a second EPS, identical but without initial condition perturbations.
Ensemble forecasts for a period of 3.5 months in spring/summer 2011 are considered. The impact of
the initial condition perturbations is studied under consideration of the prevailing weather conditions
(i.e. weak versus strong forcing of upward motion) using the concept of the convective adjustment time
scale.
Page | 35
1083
Nowcasting and forecasting quantitative precipitation amounts in mountainous
and island locations
1
2
2
2
Geoff Austin , Luke Sutherland-Stacey , Paul Shucksmith , Sijin Zhang
1
2
University of Auckland, Grafton, New Zealand, University of Auckland, Auckland, New Zealand
The operation of a combined Nowcast/Forecast rainfall system presents a number of opportunities for
the development of innovative hybrid techniques. As NWP is primarily an initial value problem, there is
a reasonable expectation that by assimilating high-resolution observations of rainfall, cloudiness and
wind speed the short-term skill of model predictions should be increased allowing a change over to
NWP from Nowcasting at an earlier stage. Important work is underway in many groups who are
attempting to assimilate radar observations of reflectivity and radial Doppler winds into convective
scale models. For an island nation such as New Zealand the particular problem is that the radar
reflectivity and radial velocity data are only available within a hundred kilometers or so of the coast
meaning that the time ahead for relevant data to be assimilated into the air mass resident over the
area of interest at the forecast time is quite limited. Possible solutions to this problem are the use of
satellite data over the surrounding ocean regions to estimate rainfall and cloudiness, which in turn can
be used in Nowcasting models the output of which can be used for direct assimilation into the NMP
system. However, the optimum way to achieve this is not clear. We present some results and illustrate
some problems for quantitative precipitation forecasts (QPF) obtained using WRF initialized with VAR
and nudging using both directly derived radar and satellite rainfall and wind speed estimates and
those obtained by Nowcasting. For mountainous regions a somewhat similar problem exists in that the
data obtained for the air mass that will produce the weather at a later time is clearly going to be
drastically modified by orographic effects as well as normal meteorological processes. Some
examples from the New Zealand Southern Alps are presented.
Page | 36
185
Data assimilation of Doppler weather radar data in WRF model for prediction of
squall events
1,2
1
3
Mohan Kumar Das , Sujit K. Debsarma , Someshwar Das
1
Theoretical Division, SAARC Meteorological Research Centre (SMRC), Dhaka, Bangladesh,
2
3
Department of Physics, Jahangirnagar University, Savar, Dhaka, Bangladesh, National Centre for
Medium Range Weather Forecasting (NCMRWF), Noida, India
Mesoscale convective systems (MCCs) are responsible for majority of the squall and hail events and
related natural hazards that occur over Bangladesh and surrounding region in pre-monsoon (March May) season. The initiation, intensification and propagation of thunderstorms are mostly governed by
the synoptic situation and localized thermodynamic conditions of the atmosphere. The topography of
the region also plays a significant role in the genesis of convective activities over the region during the
period. Prediction of these severe thunderstorms in advance is vital as it would minimize the damages
associated with them. The high-resolution Doppler Weather Radar (DWR) observation is an important
source of data for mesoscale/microscale weather analysis and forecasting. In this study, DWR
observations of Bangladesh Meteorological Department (BMD) are used during 17 April 2009, 26 May
2010, 21 May 2011 and 25 April 2012 violent squall events in order to update the initial and boundary
conditions through three-dimensional variational (3DVAR) data assimilation technique within the
Weather Research Forecasting (WRF) modeling system. Assimilation of DWR data into the model
initial conditions has shown improvement in the simulation of squalls results by capturing the surface
meteorological variables like relative humidity, temperature, reflectivity, vertical profiles of relative
humidity, vertical velocity, mixing ratio, Cloud Top Temperature (CTT) and stability indices.
Keywords: Squall, MCCs, WRF, 3DVAR data assimilation, DWR.
Page | 37
A4.1b - Accurately Quantifying Changes in Sea Ice using Satellite Remote
Sensing
08.07.2013 13:15-14:45, Sanada II
1118
About assessing uncertainties in sea ice products from satellite remote
sensing
1
2
3
4
5
Stefan Kern , Stephen Ackley , Wolfgang Dierking , Sinead Farrell , Cathleen Geiger , Katharine
6
7
8
9
10
7
Giles , Petra Heil , Juha Karvonen , Ron Kwok , Thomas Lavergne , Rob Massom , Marko
8
11
12
13
14
Mäkynen , Walt Meier , Burcu Ozsoy-Cicek , Leif-Toudal Pedersen , Stein Sandven , Vasily
15
16
13
17
18
Smolyanitsky , Gunnar Spreen , Rasmus Tonboe , Mark Tschudi , Peter Wadhams
1
Center for Climate System Analysis and Prediction, Integrated Climate Data Centre, University of
2
Hamburg, Hamburg, Germany, Laboratory for Remote Sensing and Geoinformatics, Department of
3
Geological Sciences, University of Texas at San Antonio, San Antonio, United States, Alfred
4
Wegener Institute for Polar and Marine Research, Bremerhaven, Germany, Satellite Oceanography &
Climatology Division, Cooperative Institute for Climate and Satellites, University of Maryland, College
5
Park, United States, Department of Geography, College of Earth, Ocean, and Environment,
6
University of Delaware, Newark, United States, Center for Polar Observation and Modelling,
7
University College London, London, United Kingdom, Australian Antarctic Division and Antarctic
Climate and Ecosystems, Cooperative Research Centre, University of Tasmania, Hobart, Australia,
8
9
Finnish Meteorological Institute, Helsinki, Finland, Jet Propulsion Laboratory, California Institute of
10
11
Technology, Pasadena, United States, Norwegian Meteorological Institute, Oslo, Norway, National
12
Snow and Ice Data Center, Boulder, United States, Maritime Faculty, Istanbul Technical University,
13
Istanbul, Turkey, Center for Ocean and Ice, Danish Meteorological Institute, Copenhagen, Denmark,
14
15
Nansen Environmental and Remote Sensing Center, Bergen, Norway, Arctic and Antarctic
16
Research Institute, St. Petersburg, Russian Federation, Fram Center, Norwegian Polar Institute,
17
Tromsö, Norway, Department of Aerospace Engineering, Colorado Center for Astrodynamics
18
Research, University of Colorado, Boulder, United States, Polar Ocean Physics Group, Department
of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, United
Kingdom
Sea ice is an important component of the Earth's cryosphere. Observed and expected changes in the
Earth's climate system at the high latitudes are found to be partly linked to changes in the sea ice
cover. The main characteristics describing the sea ice cover are A) the sea ice area fraction, B) the
sea ice thickness, C) the sea ice motion, D) the sea ice type, E) the degree of deformation, and F) the
surface state i.e., its snow cover and depth, and melt ponds. These characteristics have different
scales of variation both in time and space. This complicates their retrieval using satellite remote
sensing. The retrieval accuracy of one parameter is influenced by one or more of the others. For
instance, sea ice area fraction retrieval is influenced by B), D), E) and F). The characteristics of the
satellite sensor limit the retrieval accuracy additionally by a) the spatial-temporal resolution, sampling
and sampling method, b) the electromagnetic wavelength employed, and c) sensitivity to multiple
instead of just one parameter. Similar to other parameters of the Earth's hydrological cycle, like
precipitation and soil moisture, validation of satellite sea ice products is challenging. This is because of
the different spatial-temporal scales involved depending on parameter and sensing technique. As a
moving target, occurring in remote areas, sea ice needs different validation strategies than are
required, for example, for soil moisture. This contribution will comprise a review of up-to-date
achievements in satellite sea ice product uncertainty assessment and of user requirements regarding
sea ice product uncertainty. It will identify potential shortcomings in current validation methodologies
and data availability, discuss their reasons, and if possible, point out strategies to mitigate the
identified shortcomings in order to improve satellite sea ice product retrieval and uncertainty
assessment.
Page | 38
1250
Sea ice thickness from in-situ sea ice transects
1
2
2
Burcu Ozsoy Cicek , Stephen Ackley , Hongjie Xie
1
Department of Maritime Transportation and Management Engineering, Istanbul Technical University,
2
Istanbul, Turkey, Department of Geological Sciences, University of Texas at San Antonio, San
Antonio, United States
In situ transect measurements of sea ice thickness, snow depth and snow freeboard from drilling
profile lines from fifteen cruises into the Southern Ocean, Antarctica, were analyzed. Sea ice thickness
was calculated from in situ snow freeboard and depth using an isostatic approach. Sea ice thickness
was also estimated from snow freeboard. The Root-mean-square difference (RMSD) between
observed and calculated sea ice thickness reduces, and the correlation between snow freeboard and
sea ice thickness increases substantially, when 1) using values averaged over the survey lines (~50m)
and 2) using positive and negative sea ice freeboard separately. For small sea ice freeboard, however,
snow depth approximates snow freeboard pointing towards an isostatic balance also between snow
depth and sea ice thickness. Our linear regression analysis between the in situ measurements
suggests a direct conversion of snow freeboard into sea ice thickness using a region-specific set of
equations. RMSD values are similar to those obtained employing isostatic balance models and
treating positive and negative sea ice freeboard separately. However, positive and negative sea ice
freeboard cannot yet be discriminated reliably in satellite imagery. Therefore our new approach gives a
viable alternative for Antarctic sea ice thickness retrieval from altimetric measurements of snow
freeboard alone. The high correlation between in situ observations of snow freeboard and snow depth,
and the small RMSD between observed and calculated snow depth suggest the estimation of snow
depth from altimetric snow freeboard measurements. Such snow depth has similar vertical accuracy
(~5cm) as snow depth from satellite microwave radiometry, and is neither affected by snow wetness or
grain size, nor limited to snow depth < 50cm.
Page | 39
1095
Arctic sea-ice freeboard and thickness retrieval of CryoSat-2
1
1
2
1
3
Robert Ricker , Stefan Hendricks , Veit Helm , Sandra Schwegmann , Henriette Skourup , Rüdiger
1
Gerdes
1
Sea Ice Physics, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany,
2
3
Geophysics, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany, DTUSpace, Copenhagen, Denmark
Sea-ice thickness is an important variable in the polar climate system. The only remote sensing
technique capable of obtaining sea-ice thickness on basin scale are satellite altimeter missions. The
CryoSat-2 satellite is equipped with the Ku-band SAR radar altimeter SIRAL, which measures the seaice freeboard, the height of the ice surface above the local sea level.
Accurate CryoSat-2 range measurements over open water and the ice surface are necessary to
achieve the required accuracy of the freeboard to thickness conversion. In addition the range retrievals
of ice floes are influenced by variable penetration of the Ku-Band signal into the snow cover and the
surface roughness.
To constrain these error sources of the CryoSat-2 sea-ice thickness product we compare the satellite
range retrievals with validation measurements in the Arctic.
The CryoSat Validation Experiment (CryoVEx) combines field and airborne measurements in the
Arctic in order to validate CryoSat-2 data. During the CryoVEx campaign in spring 2011 in the Lincoln
Sea several Cryosat-2 underpasses were accomplished with two aircraft. One aircraft was equipped
with an airborne simulator of SIRAL and an airborne laser scanner; the second aircraft carried an
electromagnetic induction device for direct sea-ice thickness retrieval and an airborne laser scanner as
well. Both aircraft flew in close formation at the same time of a CryoSat-2 overpass.
We present our findings of the accuracy of sea-ice freeboard and thickness from CryoSat-2 data. From
the combined radar and airborne laser altimetry we can estimate the nature of CryoSat-2 range
retrievals over deformed sea ice and with the additional direct EM ice-thickness measurements we
assess the errors of the freeboard to thickness conversion. Furthermore we will present the
corresponding error estimates of the thickness retrieval, which are essential for the estimations of
trends in sea ice and the use of CryoSat-2 data.
Page | 40
1272
Interannual variability of Arctic sea ice as observed with the Soil Moisture and
Ocean Salinity Mission (SMOS)
1
1
1
Lars Kaleschke , Xiangshan Tian-Kunze , Nina Maaß
1
Institut für Meereskunde, KlimaCampus, Universität Hamburg, Hamburg, Germany
The reason for the dramatic retreat of Arctic sea ice in September 2012 is a scientific questions of
tremendous importance. Was the retreat caused by an unusual weather event or is it the expression of
a long-term thinning trend? The new data from the European Space Agency´s (ESA) Soil Moisture and
Ocean Salinity Mission (SMOS) may help to answer the question.
The 1.4 GHz brightness temperature measured by SMOS is mainly influenced by the sea ice
thickness, snow thickness, ice salinity, ice temperature and ice concentration. It has been shown that
the brightness temperature signal allows to derive the sea ice thickness up to half a meter under cold
conditions. This thickness retrieval is possible due to the relatively large penetration depth in sea ice.
Moreover, an additional snow layer further increases the brightness temperature and enables to
estimate the snow thickness from the measured brightness temperature. This approach seems to be
feasible also over thick multi-year ice.
In this presentation we analyze the available SMOS data to investigate the relation between Winter
sea ice thickness and Summer extent as well as interannual differences.
Page | 41
1174
Development of an Ice Prediction System at Environment Canada: the analysis
component
1
1
2
3
2
2
Alain Caya , Mark Buehner , Tom Carrieres , Manon Lajoie , Yi Luo , Lynn Pogson , Michael Ross
1
2
Meteorological Research Division, Environment Canada, Dorval, Canada, Canadian Ice Service,
3
Environment Canada, Ottawa, Canada, Meteorological Service of Canada, Environment Canada,
Dorval, Canada
1
An Ice Prediction System is being developed at Environment Canada. The analysis component is
based on variational data assimilation. A regional configuration of the analysis has been running
operationally in experimental mode at the Canadian Meteorological Center since March 2011. This
first version of the system assimilates sea ice concentration data derived from passive microwave
observations (SSM/I), image analysis and daily ice charts from the Canadian Ice Service. This
presentation will describe the results from testing of several major improvements to the system. The
improvements include the assimilation of SSM/IS and ASCAT satellite observations. The addition of
sea ice concentration retrievals from SSM/IS data from 3 satellites gives more robustness to the
system and improves the quality of the sea ice concentration analysis. Since ASCAT data do not
suffer from the same limitations as passive microwave data, especially during the summer season, the
2 data-sets complement each other leading to additional improvements. Moreover, an estimation of
the analysis-error standard deviation is generated to assist in the identification of potentially large
analysis error and to replace the analyzed ice concentration at these locations with surrounding
information using a smoothness constraint. Verification scores against different data-sets are shown to
measure the improvements relative to the current experimental system.
Page | 42
C6.1b - Properties and variability of the mountain snow cover
08.07.2013 13:15-14:45, Aspen II
362
Snow cover variability in a small watershed in a temperate mountain range: the
Central Spanish Pyrenees
1
1
1
1
Jesús Revuelto , Juan Ignacio López-Moreno , Cesar Azorin-Molina , Sergio M. Vicente-Serrano ,
2
Gonzalo Arguedas
1
Department of Geoenvironmental Processes and Global Change, Pyrenean Institute of Ecology
2
(Spanish Research Council), Zaragoza, Spain, Geotechnical Engineering, Cartography and
Geosciences, Universidad Politécnica de Catalunya, Barcelona, Spain
Spatial distribution of snowpack exhibits a large variability in mountain terrain. Understanding the main
factors which control snow distribution is important for assessing available water during the melting
season and studying many ecological and geomorphological processes in mountain areas.
In this study, a Terrestrial Laser Scanner (TLS) has been used with the aim of obtaining Digital Terrain
Models (DTM) of snow free and snow covered areas in a small watershed of 55ha above 2000 m.a.s.l.
in the Central Spanish Pyrenees. Thus, high resolution snow thicknesses maps have been generated
for several dates in the 2012 and 2013 snow seasons. In addition, manual measurements of snow
depth were taken within each experimental campaign in order to assess the quality of snow
thicknesses maps acquired by the TLS. Furthermore, meteorological data are continuously recorded
with an automatic weather station (AWS) which provided valuable data for later analysis. The study
area has different orientations and its topography is varied enough for analyzing the snowpack
evolution in concavities, flat areas and convexities.
Once the accuracy of resulting maps has been validated as a function of measurement distances,
linear and non-linear regression models have been applied in order to relate snow distribution with
topography, wind exposure and shielding of the different basin zones. This experimental study has
enabled to get results on the main factors which explain snow distribution in the catchment and to
assess whether if the role of such factors is constant in time or exhibits intraanual and interannual
variability. New results have highlighted the strong spatial variability of snowpack in the Central
Spanish Pyrenees. In particular, the snow redistribution by wind and exposure to solar radiation exerts
a key role in the snow accumulation in the basin. However, this impact is subjected to large variations
between the different analysed surveys.
Page | 43
108
Persistence in intra-annual snow depth distribution. Part I: measurements and
topographic control
1,2
2
2,3
Michael W. Schirmer , Michael Lehning , Vanessa Wirz
1
2
Applied Snow and Avalanche Research, University of Calgary, Calgary, Canada, WSL Institute for
3
Snow and Avalanche Research SLF, Davos, Switzerland, University of Zurich, Zurich, Switzerland
Terrestrial and Airborne Laser Scanning (TLS and ALS) techniques have only recently developed to
the point where they allow wide-area measurements of snow distribution in varying terrain. In this
paper we present multiple TLS measurements showing the snow depth development for a series of
precipitation events. We observe that the pattern of maximum accumulation is similar for the two years
presented here (correlation up to r=0.97). Storms arriving from the Northwest show persistent snow
depth distributions and contribute most to the final accumulation pattern. Snow depth patterns of
maximum accumulation for the two years are more similar than the distribution created by any two
pairs of individual storms. Based on the strong link between accumulation patterns and terrain, we
investigated the ability of a model based on terrain and wind direction to predict accumulation patterns.
This approach of (Winstral et al., 2002), which describes wind exposure and shelter, was able to
predict the general accumulation pattern over scales of slopes but failed to match observed variance.
Furthermore, a high sensitivity to the local wind direction was demonstrated. We suggest that
Winstral´s model could form a useful tool for application from hydrology and avalanche risk
assessment to glaciology.
Page | 44
471
Analysis of multi-annual end-of-season snow accumulation patterns from
LiDAR data
1,2
1
1,3
2
Kay Helfricht , Katrin Schneider , Johannes Schöber , Michael Kuhn
1
2
alpS Centre for Climate Change Adaptation Technologies, Innsbruck, Austria, Institute of
3
Meteorology and Geophysics, University of Innsbruck, Innsbruck, Austria, Institute of Geography,
University of Innsbruck, Innsbruck, Austria
Spatially distributed modelling of the mountain snow cover is of importance for a realistic prediction of
runoff generation from melt water. However, data of snow depths is mostly available only on the point
scale for model calibration and validation. Information on the spatial distribution of snow depths is
sparse. Surface elevation changes derived from LiDAR can be interpreted as snow depth to analyse
snow accumulation patterns in complex alpine topography. Airborne Laser Scanning (ALS) provides
this inormation on the catchment scale with a high resolution of less than 1 meter. The question is
whether and where this distribution is representative for the mean spatial distribution of the snow cover
in these catchments on a multi-annual time scale. For a small glacierized catchment (approx. 36 km²)
in the Ötztal Alps (Tirol, Austria) maps of the spatial distribution of surface elevation changes are
available for five accumulation seasons. These maps where analysed regarding the multi-annual
persistence and the variability of the snow accumulation patterns. The study aims to evaluate the
validity of zones with similar characteristics. In the five accumulation seasons under consideration,
snow covered area is less variable than mean annual snow depth. In the catchment areas next to the
mountain ridges snow depth distribution is controlled by wind exposure and slope. In the lower
elevation zones energy balance is responsible for differing snow depths, which can be related to the
topographic controls elevation and aspect. An increased snow accumulation compared to
unglacierized areas is obvious on glacier surfaces in all five years. The multi-annual analysis reveals
typical release and accumulation zones of avalanches. Likewise, singular avalanche events which do
not occur regularly can be detected. Areas influenced by wind redistribution can be delineated from
typical accumulation patterns on the glaciers.
Page | 45
233
Understanding snow accumulation patterns in an highly glacierized alpine
catchment
1
1
1
Ilaria Clemenzi , Francesca Pellicciotti , Paolo Burlando
1
Institute of Environmental Engineering, ETH Zurich, Zurich, Switzerland
Snow depth variability is determined by multiple processes acting at different spatial and temporal
scales (precipitation deposition, transports by wind and redistribution due to avalanches). A way to
explore snow spatial distribution is to use fractal analysis determining fractal dimensions and scale
breaks. Numerous studies have used this approach to characterise snow distribution at a variety of
spatial scales and temporal resolutions. Several have used this approach to identify the inter-seasonal
consistency of snow accumulation patterns or to compare patterns between different basins. Only few
have looked at intra-seasonal variability and fewer have focused on snow depth scaling properties in
glacierized catchments. We investigate the spatial and inter-seasonal variability of snow accumulation
patterns over Haut Glacier d'Arolla in the Swiss Alps during two accumulation seasons (2006-2007
and 2010-2011). The focus of our work is whether the snow depth distribution at the end of the
accumulation season is consistent between the two seasons. We use DEMs generated by high
resolution helicopter-borne LiDAR-data and calculate snow accumulation as the difference between
them. We investigate the spatial structure of snow depth in subareas in the upper basin and on the
tongue for the two years, calculate the omnidirectional and directional variograms and describe the
snow depth scaling behaviour through the fractal dimension. Interannual consistency in the
accumulation patterns can be observed between the two years. Further, we find a distinct behaviour
on the tongue and in the upper basin: subareas on the tongue are characterized by a difference in the
fractal dimension for the two perpendicular directions of North-South and East-West. This is not
evident in the upper area. We interpret this as the result of the exposition of these areas to the
prevailing wind direction observed during the considered period, which result particularly influenced by
the topographic features of the catchment.
Page | 46
1252
High-resolution modeling of wind-induced snow transport using a fully coupled
snowpack/atmosphere model
1,2
2
2
3
4
Vincent Vionnet , Eric Martin , Valery Masson , Gilbert Guyomarc'h , Florence Naaim Bouvet ,
5
3
2
Alexander Prokop , Yves Durand , Christine Lac
1
2
Meteorological Research Division, Environment Canada, Dorval, Canada, CNRM-GAME (Météo3
France-CNRS), Toulouse, France, CNRM-GAME/CEN Météo-France/CNRS, Saint Martin d'Heres,
4
France, IRSTEA, UR ETGR Erosion Torrentielle Neige et Avalanches, Saint Martin d'Heres, France,
5
Institue of Mountain Risk Engineering, BOKU University, Vienna, Austria
In alpine regions, blowing snow events strongly influence the spatio-temporal evolution of the snow
cover throughout the winter season. To gain understanding on the complex processes that drive the
redistribution of snow during such events, we used the recently developed simulation platform MesoNH/Crocus. This coupled system consists in the detailed snowpack model Crocus and the
atmospheric model Meso-NH. Meso-NH/Crocus simulates snow transport in saltation and in turbulent
suspension and includes the sublimation of suspended snow particles.
We present the first detailed evaluation of the model against data collected around the experimental
site of Col du Lac Blanc (2720 m a.s.l., French Alps). For this purpose, a blowing snow event without
concurrent snowfall has been selected and simulated. Results show that the model captures the main
structures of atmospheric flow in alpine terrain, the vertical profile of wind speed and the snow
particles fluxes near the surface. However, the horizontal resolution of 50 m is found to be insufficient
to simulate the location of areas of snow erosion and deposition observed by terrestrial laser scanning.
When activated, blowing snow sublimation causes a reduction in deposition of 5.3 %. Total
sublimation (surface + blowing snow) is three times higher than surface sublimation in a simulation
neglecting blowing snow sublimation.
Page | 47
A6.1b - Advances in ice sheet modelling
08.07.2013 13:15-14:45, Forum
1257
Adjoint-based sensitivities and data assimilation with a time-dependent marine
ice sheet model
1
1
Daniel Goldberg , Patrick Heimbach
1
Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge,
United States
To date, assimilation of observational data using large-scale ice models has consisted only of timedependent inversions of surface velocities for basal traction, bed elevation, or ice stiffness. These
inversions are for the most part based on control methods (Macayeal D R, 1992, A tutorial on the use
of control methods in ice sheet modeling), which involve generating and solving the adjoint of the ice
model. Quite a lot has been learned about the fast-flowing parts of the Antarctic Ice Sheet from such
inversions. Still, there are limitations to these "snapshot" inversions. For instance, they cannot capture
time-dependent dynamics, such as propagation of perturbations through the ice sheet. They cannot
assimilate time-dependent observations, such as surface elevation changes. And they are problematic
for initializing time-dependent ice sheet models, as such initializations may contain considerable model
drift.
We have developed an adjoint for a time-dependent land ice model, with which we will address such
issues. The land ice model implements a hybrid shallow shelf-shallow ice stress balance and can
represent the floating, fast-sliding, and frozen bed regimes of a ma rine ice sheet. The adjoint is
generated by a combination of analytic methods and the use of automated differentiation (AD)
software. Experiments with idealized geometries have been carried out; adjoint sensitivities reveal the
"vulnerable" regions of ice shelves, and preliminary inversions of "synthetic" observations (e.g.
simultaneous inversion of basal traction and topography) yield encouraging results.
Page | 48
800
Influence of anisotropy on the local flow at Scharffenbergbotnen blue ice area,
East Antarctica
1
2
3
2,4,5
Thomas Zwinger , Martina Schäfer , Carlos Martín , John C. Moore
1
2
CSC - IT Center for Science Ltd., Espoo, Finland, Arctic Centre, University of Lapland, Rovaniemi,
3
4
Finland, British Antarctic Survey, Cambridge, United Kingdom, College of Global Change and Earth
5
System Science, Beijing Normal University, Beijing, China, Department of Earth Sciences, Air, Water
and Landscape Science, Uppsala University, Uppsala, Sweden
Blue Ice Areas (BIA), making up a total of 1% of the glaciated surface area of the Antarctic Ice Sheet,
are characterized by the presence of a sublimation driven ablation zone that contains ancient ice at
their surface. This potentially renders BIAs good sources for paleoclimate sampling, since the ice is
much more accessible than from vertically drilled cores on ridges or domes. Another clear advantage
of BIAs are generally the reasonable proximity to the coast, which facilitates the study the Southern
Ocean influence on the climate signal. The complex nature of the ice flow implies that the
interpretation of such ice-cores requires enhanced ice flow modeling. First results obtained with the
high-resolution, full-Stokes model Elmer/Ice using the standard non-linear thermo-mechanically
coupled Glen´s flow law revealed a huge discrepancy compared to observed velocity measurements.
We were unable to be overcome this by the usual tuning parameters (enhancement factor,
temperature, geothermal heat flux) that influence the flow law. By prescribing different fabric
distributions and introducing a non-collinear orthonormal anisotropy flow law (GOLF) were able to get
a satisfying match between observed and simulated velocities. Further simulations with the obtained
velocity distribution revealed that the age/depth and surface distribution is far from being in a steady
state and not in agreement with the few reliable age measurements. In order to fully understand the
surface distribution in such ice-cores a transient simulation starting from the Late Glacial Maximum
including the correct initial conditions for geometry, age/depth and fabric as well as temperature
distribution would be needed.
Page | 49
1034
Combining climate and GIA modelling: a novel approach to resolving the
Antarctic ice core record over interglacials
1
Matthew Whipple
1
University of Bristol, Bristol, United Kingdom
East Antarctic ice cores show, to first order, a record of interglacial temperature. However, other
factors, such as changes in the source isotopes mean that this is far from a perfect temperature
record. Climate models can show part of the signal, but so far, have missed a significant signal at
previous interglacials, as changes in elevation have not been accounted for.
Here, I simulate the LIG climate via a series of HAD CM3 snapshot models, and combine it with
Glacial Isostatic Adjustment (GIA) models for East Antarctica, showing changes in ice sheet elevation
over the last interglacial (LIG), compared to this interglacial. A climate sensitivity experiment shows
East Antarctica will not show much significance to a reduction in the West Antarctic ice sheet (WAIS).
The changing ice sheet is constrained using paleo sea level data, where we assess areas susceptible
to ice sheet reduction, with a removed WAIS at the LIG.
Overall, the combined modeling shows a good fit to East Antarctica with reduced thickening by up to
100m at the LIG. Unresolved models and data show evidence for changes in the lapse rate at warmer
temperatures. Although highly dependent on modelling the timing of events, a combination of climate
and GIA modelling goes some way to resolving the signal.
Page | 50
690
Analyzes of Greenland ice sheet evolution within a new unstructured gridbased glacial modelling framework
1
1
Gordan Stuhne , W R. Peltier
1
Department of Physics, University of Toronto, Toronto, Canada
We will discuss the formulation and results of new simulations of the Greenland ice sheet, as
performed within a state-of-the-art glacial modeling framework that replaces older versions of the
University of Toronto Glacial Systems Model (UofT GSM). This framework incorporates an
unstructured grid-based dynamical core that can, employing numerical methods developed by us and
by other research groups, represent the evolution of land ice masses at different levels of physical
approximation. Highly parallelizable discontinuous Galerkin (DG) techniques work well for 2-D
advective dynamics like those arising in the shelfy-stream approximation (SSA), but have not yet been
successfully adapted to the 3-D physics of the shallow-ice approximation (SIA), the higher-order
Blatter-Pattyn (BP) model, or the Full Stokes (FS) model. The original UofT GSM was restricted to the
SIA discretized on structured grids,
and its primary novelty was in a sophisticated representation of the glacial isostatic adjustment (GIA)
process. We subsequently developed unstructured mesh generation and data processing techniques
that were applied first to 2-D DG simulations, and then to 3-D simulations using a dynamical core
developed at the Jet Propulsion Laboratory. New boundary conditions for more advanced physics are
being introduced along with further improvements of our meshing techniques, and the implications will
be discussed with reference to a new set of Greenland simulations.
Page | 51
857
Consequences of raising CO2 concentrations for Greenland and the interacting
climate: fully bidirectionally coupled ice sheet-earth system model simulations
1,2
3
1
Christian Rodehacke , Miren Vizcaino , Uwe Mikolajewicz
1
2
Ocean in the Earth System, Max Planck Institute for Meteorology, Hamburg, Germany, Danish
3
Meteorological Institute, Copenhagen, Denmark, Institute for Marine and Atmospheric Research
Utrecht (IMAU), Utrecht University, Utrecht, Netherlands
The observed Arctic warming enhances melting in Greenland, which releases additional fresh water
into the ocean. Ongoing melting could stabilize the water column in the adjacent deep water formation
sides. With our fully coupled ice sheet-earth system model we analyze if this weakens the formation of
deep water and reduces the Atlantic meridional overturning circulation (MOC). We´ve performed
idealized projections to investigate the response of our two-way coupled system under raising
atmospheric CO2.
We will present our fully coupled system including its physical based surface mass balance calculation
and ice sheet-ocean interaction; The ESM receives for example orographic changes and fresh water
fluxes. Since the ice sheet´s near future depends on both the external forcing and its initial state, we
have performed Latin-Hyper-Cube ice sheet model simulations for at least one glacial-interglacial
cycle to obtain a reasonable initial state.The best performing LHC member is exposed to boundary
conditions determined from energy balance calculations. Finally the fully coupled system is brought
into a quasi-equilibrium under pre-industrial conditions before scenarios are started. Our coupled ice
sheet inherits the memory of a glacial cycle simulations and we do neither apply flux corrections nor
utilize anomaly coupling.
Under different CO2 forcing scenarios the response of the coupled system is analyzed. For instance,
an abrupt CO2 quadruplication triggers an immediate response of the Greenlandic ice sheet. The
surface mass balance turns strongly negative within years causing skyrocketing melting rates. The
contribution of the ocean-ice sheet interaction decreases, because the ice sheets retreats from the
coasts. The additionally released fresh water stifle potentially the MOC. However, in our model system
the additional fresh water has a negligible influence on the MOC within a few centuries.
For the study we used the MPI-ESM (ECHAM6-JSBACH: T63L47, MPIOM-HAMOCC: GR15L40),
which interacts with PISM covering Greenland at 10km resolution.
Page | 52
C2.3a - Clouds, aerosols and precipitation at high latitudes
08.07.2013 13:15-14:45, Studio
1167
A comparison of in-situ Arctic and Antarctic cloud microphysics
measurements
1
1
1
1
1
1
Keith Bower , Tom Choularton , Martin Gallagher , Jonny Crosier , Gary Lloyd , Ian Crawford , Dan
1,2
3
Grosvenor , Tom Lachlan-Cope
1
Centre for Atmospheric Science (CAS), CAS, SEAES, University of Manchester, Manchester, United
2
Kingdom, Department of Atmospheric Science, University of Washington, Seattle, United States,
3
British Antarctic Survey, Cambridge, United Kingdom
Some of the first detailed in-situ aircraft observations of the microphysics of Antarctic clouds around
the Antarctic Peninsula and Larsen Ice shelf will be presented. These measurements were made in
February 2010 using the British Antarctic Survey´s Twin Otter aircraft. The clouds were mostly found
in the free troposphere and spanning the temperature range 0 to -21°C . They contained supercooled
water at most temperatures and ice crystals in concentrations of 0.07 per litre or less, generally of the
same order as primary IN concentrations predicted by some parameterisations, but significantly less
than predicted by other IN parameterisations in this pristine environment. At other times, ice
concentrations were significantly enhanced, suggesting strong secondary ice production mechanisms
were operating on such occasions.
By contrast, measurements will be presented from clouds measured in the Arctic over the sea-ice
margins during the period of maximum ice extent around Svalbard, during March-April 2013. These
measurements will be made by both the Twin Otter and the larger Facility for Airborne Atmospheric
Measurement (FAAM) BAe-146 aircraft as part of the ACCACIA experiment. Measurements of the
aerosol above and below these clouds (and at the sea surface by ship) will also be made to
understand the aerosol-cloud interactions occurring, in a period where advected polluted airmasses
are expected to dominate.
Page | 53
1234
Exploring the connection between aerosol and ice generation in stratiform
mixed-phase clouds by combining satellite and airborne observations
1
2
2
3
4
Zhien Wang , Damao Zhang , Min Deng , Andrew Heymsfield , Dong Liu
1
2
Dept. 3038, University of Wyoming, Laramie, United States, University of Wyoming, Laramie, United
3
4
States, NCAR, Boulder, United States, Anhui Institute of Optics and Fine Mechanics, Chinese
Academy of Sciences, Key Laboratory of Atmospheric Composition and Optical Radiation, Hefei,
United States
To better understand the connections of aerosols and ice generation in the atmosphere, we developed
an approach using CloudSat radar and CALIPSO lidar measurements to quantitatively determine ice
concentrations in stratiform mixed-phase clouds and link them with aerosol conditions. With integrated
airborne remote sensing and in-situ sampling measurements and 1-D ice particle growth model
calculations, we established the relationship of ice number concentration and layer maximum radar
reflectivity (Ze_max) in stratiform mixed-phase clouds. Evaluation results indicated that ice crystal
number concentration in stratiform mixed-phase clouds can be estimated within uncertainties of about
a factor of 2 statistically. Four years of collocated CALIPSO and CloudSat measurements are used to
identify mid-level supercooled stratiform clouds (MSSCs). Systemic differences of ice generation in
similar MSSCs in terms of cloud top temperature (CTT) and liquid water path are found between
Northern and Southern hemispheres. For example, MSSCs in the Arctic Regions contain a factor of ~
3 higher ice concentrations than those in the Antarctic Regions. For the same CTT, over the Arctic
Region we observed a factor of 4 higher ice concentrations during March-April-May than during the
rest of the year. Collocated CALIPSO and CloudSat measurements are used to quantify the impact of
dust on heterogeneous ice generation in MSSCs over the 'dust belt'. The results show that the dusty
MSSCs have an up to 20% higher mixed-phase cloud occurrence and up to 8 dBZ higher mean
Ze_max than similar MSSCs under background aerosol conditions. The observed Ze_max differences
suggest that dust could enhance the ice particle concentration in MSSCs by a factor of 2 to 6 at
temperatures colder than -12 °C. The enhancements are strongly dependent on the CTT, the
concentrations of large dust particles and chemical compositions.
Page | 54
307
A new satellite perspective on polar precipitation
1
2
Tristan L'Ecuyer , Norman Wood
1
Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison, Madison,
2
United States, Space Science and Engineering Center, University of Wisconsin-Madison, Madison,
United States
The W-band Cloud Profiling Radar (CPR) aboard the CloudSat satellite provides a new perspective on
the global character of falling snow that has been difficult to detect using conventional space-borne
precipitation sensors. This presentation will describe algorithms that have recently been developed to
characterize the distribution of high latitude precipitation using CPR observations. Inferred distributions
of polar precipitation and their annual cycle will be highlighted to illustrate the potential value of
CloudSat observations for constraining the precipitation component of ice sheet mass balance. The
sensitivity of millimeter-wavelength reflectivities to ice crystal shape and particle size distribution can,
however, lead to large uncertainties in retrieved snowfall rates. A new approach will be outlined for
mitigating these uncertainties using complementary remote and in situ observations collected during
recent field experiments. The method employs high resolution radar reflectivity, snowfall rate, and
size-resolved fall speed measurements to provide statistical constraints on the scattering and fallspeed relationships that lie at the root CloudSat's snowfall algorithm. Within this framework, the
CloudSat snowfall algorithm can be thought of as exporting the information provided by ground-based
instrumentation to global scales.
Page | 55
449
Ice particle type and microphysics in high latitudes by spaceborne active
sensors: regional characteristics and annual variability
1
1
1
2
Hajime Okamoto , Kaori Sato , Yuichiro Hagihara , Hiroshi Ishimoto
1
2
Research Institute for Applied Mechanics, Kyushu University, Kasuga, Japan, Meteorological
Research Institute, Tsukuba, Japan
We examined ice particle types and microphysics in high latitudes by using space-borne active
sensors between 2006 and 2012. We developed series of algorithms to retrieve cloud properties by
using 95GHz cloud radar on CloudSat and dual-wavelength polarization lidar on CALIPSO. By
combining these information, the cloud particle types were classified as three-dimensional ice particles
(3D-ice), horizontally oriented ice plates (2D-plate), water and solid and liquid precipitation. The
fraction of 2D-plates was larger in high latitude regions than in other regions. Ice microphysics was
also studied by combined use of radar reflectivity factor from CloudSat, and lidar backscattering
coefficient and depolarization ration from CALIPSO. The vertical and latitudinal distribution of ice
particle types and microphysics and their annual variability were also examined. The maximum altitude
of clouds is about 10km in high latitudes and that for super cooled water is about 5km. IWC decreased
as altitude decreased and zonal mean of the maximum IWC and effective radius were 0.05 g/m^3 and
150µm, respectively. The large particles >100µm were found below 5km in high latitude (>70 degrees
north). Land-ocean differences were also noticeable. The IWC was smaller over ocean than over land
and ice effective radius was larger over ocean. These properties were further analyzed in relation to
temperature and water vapor amount as well as super saturation using ECMWF and AIRS data in
order to reveal the formation mechanism of ice particles and its variability.
Page | 56
646
Correction of cloud 3D radiative effects to improve MODIS aerosol retrieval
near clouds
1,2
1
1,3
4
5
Guoyong Wen , Alexander Marshak , Robert Levy , Lorraine Remer , Norman Loeb , Tamas
1,4
1
Varnai , Robert Cahalan
1
2
Cimate and Radiation Lab, NASA/Goddard Space Flight Center, Greenbelt, United States, GESTAR,
3
4
Morgan State University, Baltimore, United States, SSAI, Greenbelt, United States, JCET, University
5
of Maryland Baltimore County, Baltimore, United States, NASA Langley Research Center, Hampton,
United States
We perform case studies on correcting 3D cloud adjacency effects for Aqua MODIS granules. In this
process, we use CALIPSO observations to ensure that both clouds and aerosols embedded in the
boundary layer. We use CERES observations on the same platform to derive narrowband upward flux,
and further to estimate cloud induced reflectance from a 2-layer model. We use the corrected
reflectance as inputs to the MODIS aerosol retrieval algorithm to obtain corrected aerosol properties in
the vicinity of clouds. We find that the correction leads to smaller values in aerosol optical thickness
(AOT), the Ångström exponent, and the small mode fraction of AOT, it also makes the average
aerosol particle size near clouds larger than far away from clouds, which is more realistic than the
opposite behavior observed in operational retrievals. We discuss issues in the current correction
method as well as our plans to validate the algorithm.
Page | 57
758
Retrieving ice and water cloud properties over bright surfaces from shortwave
spectral observations
1
1
1
Sebastian Schmidt , Odele Coddington , Peter Pilewskie
1
Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, United States
Observations of clouds over snow- and ice-covered terrain are challenging for space-borne passive
shortwave imagers because of the lacking contrast between the bright surface and the clouds,
especially when only a handful of spectral channels are available. We explore how clouds can be
better distinguished against the bright background when using spectrally contiguous reflectance
observations in the near-infrared, and which cloud parameters can be reliably retrieved, given the
spectral variability of the underlying surface albedo.
Page | 58
B3.2b - Dynamics of mountain weather and climate
08.07.2013 13:15-14:45, Wisshorn
287
Triggering of orographic convection and precipitation
1
Ronald Smith
1
Geology and Geophysics, Yale University, North Haven, United States
The Dominica Experiment (DOMEX) took place in the eastern Caribbean from April 4 to May 10, 2011
with 21 research flights of the Wyoming King Air and several other observing systems. The goal was
an improved understanding of the physics of convective orographic precipitation in the tropics. Two
types of convection were found. During a period of weak trade winds, diurnal thermal convection was
seen over Dominica. This convection caused little precipitation, in part because of island- derived
aerosol and reduced precipitation efficiency. During periods of strong trades, mechanically forced
convection over the windward slopes brought heavy rain to the high terrain. This convection is
triggered by moist cool air parcels, initially buoyancy adjusted, that are suddenly lifted by the terrain. In
this mechanically-forced convection, air parcels did not touch the island surface to gain buoyancy so
no island derived aerosols were lofted. The DOMEX data set will advance our understanding and test
our theories of cumulus triggering and aerosol influence on precipitation.
Page | 59
876
Sensitivity of extreme precipitation events in Switzerland to moisture variations
(with high-resolution numerical model COSMO)
1
2
1
Nicolas Piaget , Felix Naef , Heini Wernli
1
2
Institute for Atmosphere and Climate Science, ETH, Zurich, Switzerland, Institute of Environmental
Engineering, ETH, Zurich, Switzerland
Dimensioning of flood protections is based on the estimation of the probable maximum flood (PMF). A
reliable estimate of this quantity can only be made using a realistic estimate of the probable maximum
precipitation (PMP) in the considered catchment. However, traditionally used procedures to estimate
PMP are not well suited for mountainous regions. These procedures typically transfer an extreme
precipitation event observed in a nearby area to the catchment of interest with some adaptation for its
topography. But complex terrain does strongly affect precipitation distribution and impose strong
nonlinearities for precipitation resulting from small variations in the atmospheric flow conditions.
Therefore an in-depth knowledge of the precipitation characteristics of a catchment is needed to
obtain realistic estimates of PMP.
We use the high-resolution numerical model COSMO to study small-scale processes induced by
topography-flow interactions. A sensitivity analysis is performed to determine the influence of subtle
variations in atmospheric parameters such as specific humidity, wind direction, and temperature on the
precipitation distribution. For this purpose, various approaches are used to modify either the initial and
boundary conditions of humidity and temperature, or the wind field via a synthetic PV modification and
PV inversion. Simulations are performed for different flood events in Switzerland, including the 1991
event in a Jura mountains catchment and the 2011 event in a Bernese Oberland catchment.
The results show that, for instance an increase of the specific humidity of the incident flow does not
necessarily produce an increase of precipitation in the target catchment. Indeed, with increased
ambient moisture, smaller mountains upstream of the catchment can be more efficient in triggering
precipitation and therefore reduce the moisture available downstream. This novel approach with a set
of synthetic sensitivity experiments allows estimating, for a particular catchment, the physical limits of
the PMP value.
Page | 60
367
Rapid transport of stratospheric ozone into the mountainous planetary
boundary layer
1
1
1
1
Bojan Skerlak , Michael Sprenger , Stephan Pfahl , Harald Sodemann , Heini Wernli
1
IAC, ETH Zurich, Zürich, Switzerland
1
Stratosphere-troposphere exchange (STE) has an important impact on atmospheric chemistry: it
changes the oxidative capacity of the troposphere and potentially also affects the climate system.
Although most ozone in the troposphere is produced photochemically, stratospheric ozone can be
brought into the troposphere during STE events. Of particular interest are so-called deep exchange
events where ozone-rich stratospheric air reaches the planetary boundary layer (PBL) within a few
days (deep STT). This rapid vertical transport can contribute to ozone concentrations at ground level
and affect plant and human physiology. It is therefore not only important to quantify the ozone flux
across the tropopause but also to investigate the transport and mixing after the crossing. Using a
Lagrangian methodology and 33 years of ERA-Interim reanalysis data, we have compiled a global
climatology of STE from which the Plateau of Tibet and the Rocky Mountains can be identified as ´hot
spots´ of deep STT in boreal winter and spring. To adress the question of how the stratospheric air
masses are transported into the PBL in more detail, we investigate case studies in these regions with
the mesoscale numerical weather prediction model COSMO. On this account, we initialize a passive
tracer in the stratosphere using an elaborated 3d-labelling algorithm which applies the dynamical 2
pvu/380 K tropopause definition. This tracer is then advected by both resolved and parameterized
processes and allows us to follow the stratospheric air masses along their journey into the
mountainous PBL. Tracer levels at the lowest model level can be compared to ozone measurements
at remote high-altitude stations and first results are promising.
Page | 61
1229
Intensification process of a broad snowband on a flank of a mountain region
during a cold-air outbreak
1
1
2
1
Tadayasu Ohigashi , Kazuhisa Tsuboki , Yukari Shusse , Hiroshi Uyeda
1
2
Hydrospheric Atmospheric Research Center, Nagoya University, Nagoya, Japan, National Research
Institute for Earth Science and Disaster Prevention, Tsukuba, Japan
During a cold-air outbreak between 25 and 27 January 2009, a broad snowband formed along the
coastal region on the Sea of Japan side. On the flank of a mountain region, precipitation from the
snowband intensified, and its amount reached more than twice that in other regions of the snowband.
Intensification processes of the broad snowband and microphysical characteristics of snowfall
intensification are examined. During the lifetime of the snowband, two low-pressure systems
successively developed in the central Sea of Japan. In the coastal region to the south of the lowpressure systems, westerly winds are dominant. The non-dimensional mountain height shows that
westerly flow should be blocked at least below a height of 1000 m by a high mountain region. The
blocked flow region showed a large pressure gradient force. When predominant westerly winds flow
into the large pressure gradient region, unbalanced flow with sub-geostrophic wind speeds forms. The
relatively high pressure forced the westerly flow toward the left, resulting in southwesterly winds. The
southwesterlies made a convergence with the predominant westerlies, the area of which corresponded
to that of snowfall intensification. The radar reflectivity maximum in the intensified region was more
than or equal to 35 dBZ during one-third of the 2-day lifetime of the cloud band. Polarimetric
parameters (ρhv and KDP) indicated that dry and vertically-oriented particles were dominant in the
intensified echoes. This particle type seems to be dry conical graupel.
Page | 62
1189
Surface-atmosphere exchange over strong topography
1
1
1
1
Mathias Rotach , Ivana Stiperski , Alexander Gohm , Johanes Wagner
1
Institute for Meteorology and Geophysics, University of Innsbruck, Innsbruck, Austria
Earth-Atmosphere interaction is generally understood to take place at the surface and to be
determined by the abundance of energy, matter or momentum on the one hand, and by the efficiency
of turbulent exchange on the other hand. Hence the net exchange between the surface and the free
troposphere is chiefly determined by the characteristics of the atmospheric boundary layer (exchange
efficiency). In numerical models processes related to this turbulent transport are usually parameterized
(except for very high-resolution LES simulations). For sensible heat and trace gases such as water
vapour, parameterizations employed are based on knowledge on boundary layer processes from flat
and horizontally homogeneous terrain. Over complex terrain, however, exchange of heat, mass and
momentum is not only controlled by turbulence, but also through meso-scale processes like thermodynamically driven meso-scale circulations. These are larger in scale than turbulence but smaller than
(or comparable to) the resolution of most numerical models. Thus they need to be parameterized (in
coarse resolution models) or their interaction with turbulence needs to be known. For momentum it
has long been recognized that parameterizations for turbulent exchange alone are not even sufficient
to reproduce mean flow magnitudes (nothing to say about local flow patterns) and therefore
additionally, gravity wave drag parameterizations have been introduced in order to take into
consideration the additional drag due to the effect of subgrid-scale topography.
In this contribution we hypothesize that also for the exchange of heat and mass over topographically
influenced regions subgrid scale processes such as local circulations or geometrical effects may play
an important role in altering the pure surface exchange due to turbulent transport. Some results from
combined observational/ numerical studies will be reviewed in support of this hypothesis and possible
consequences, e.g. for carbon budgeting in complex terrain will be discussed.
Page | 63
A3.1b - ENSO and decadal variability under climate change
08.07.2013 13:15-14:45, Schwarzhorn
379
Annual cycle and interannual variability in the tropical Pacific as simulated by
three versions of FGOALS
1
1
1
Yongqiang Yu , Jie He , Weipeng Zheng , Yihua Luan
1
Institute of Atmospheric Physics, Beijing, China
1
The simulated seasonal cycle and interannual variability in the tropical oceans with three versions of
the LASG/IAP Flexible Ocean-Atmosphere-Land System (FGOALS) model that have participated the
phases 3 and 5 of Coupled Model Intercomparison Project (CMIP3 and CMIP5) are presented in this
study. These three versions are FGOALS-g1.0, FGOALS-g2 and FGOALS-s2, respectively.
The seasonal cycle of sea surface temperature (SST) in tropical Pacific is realistically reproduced by
the versions g2 and s2 of FGOALS, while it is poorly simulated in the previous g1.0. Three feedback
mechanisms responsible for SST annual cycle by three coupled GCMs in the eastern Pacific are
evaluated. The ocean-atmosphere dynamic feedback that are successfully reproduced in both
versions s2 and g2 plays a key role in determining SST annual cycle, while the overestimated stratus
cloud - SST feedback amplifies the annual cycle in the model FGOALS-s2.
The version g1.0 simulates much stronger ENSO events than observation with very regular period
about 3 years and negative skewness, but the other two versions g2 and s2 of FGOALS successfully
simulate ENSO amplitude, and period as observed and positive asymmetry but with less strength.
Further ENSO feedback analyses suggest that the surface solar radiation feedback is principally
responsible for the overestimated ENSO amplitude in the version g1.0. Both two versions g1.0 and s2
can simulate two different types of El Niño events, but the version g2 can simulate EP El Niño only,
because the simulated negative SST cloud feedback by the version g2 is much stronger in central
Pacific than observation and other two versions, that prevents the version g2 from developing CP El
Nino events.
Page | 64
1124
Recent progress in the MIROC5 seasonal prediction system and predictability
of two flavors of El Nino
1
1
2
1
Yukiko Imada , Masahide Kimoto , Masayoshi Ishii , Masahiro Watanabe
1
2
Atmosphere and Ocean Research Institute, University of Tokyo, Chiba, Japan, Meteorological
Research Institute, Tsukuba, Japan
We developed a seasonal prediction system using the coupled atmosphere‐ocean general circulation
model (AOGCM) MIROC5 co‐developed by Atmosphere and Ocean Research Institute (AORI),
National Institute for Environmental Studies (NIES), and Japan Agency for Marine‐Earth Science and
Technology (JAMSTEC). The spatial resolution is a horizontal triangular spectral truncation at total
wave number 85 (T85) with 40 vertical layers, and eight ensemble forecast members are generated
according to the protocol of the WCRP Climate‐system Historical Forecast Project (CHFP). Hindcast
products for the period 1979‐2011 show high predictability of tropical climate signals with the
significant anomaly correlation coefficient skill scores, even though the ocean anomaly data
assimilation is applied to the initialization process.
We assess the difference of the seasonal predictability for two prominent types of El Nino, traditional
eastern Pacific (EP) events and central Pacific (CP) events. Overall, the predictable months of CP
events are shorter than EP events. Characteristics of each error-growing process are also
investigated. We will also discuss the decadal change of ENSO prediction skill.
Page | 65
109
Delayed remote response to ENSO over India Ocean and in polar stratosphere
1
Rongcai Ren
1
LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
Niño-Southern Oscillation (ENSO) influences global weather and climate far away from the tropical
Pacific basin through its excitation of atmospheric teleconnection or atmospheric bridge processes. In
this talk, I will present observational evidence for two types of delayed remote response: one over
India Ocean Basin (IOB) and the other in polar stratosphere.
In general, IOB SST is warmer in the spring after an El Niño in winter and vice versa. We found that
the seasonal timing of the decay phase of El Niño events during the period from the late 1940s to the
early 2000s has been delayed from spring to early summer since 1970s, while the seasonal timing of
La Niña decay phase remains in spring season. The direct effect of the later decay of El Niño events is
the lengthening of the delayed warming effect of El Niño on IOB into summer, attributing to the
interdecadal warming over IOB in summer season from the late 1940s to the early 2000s.
In general, there exists a negative correlation between ENSO and Polar vortex strength, but the
maximum negative correlation is found in the next winter season after mature phase of ENSO event,
rather than in the concurrent winter. Following a warm ENSO event, the stratospheric polar vortex
tends to be anomalously warmer and weaker in both the concurrent and the next winter season and
vice versa. However, polar warming/cooling anomalies after a warm/cold ENSO event in the next
winter are stronger and with a deeper vertical structure than those in the concurrent winter. This
delayed effect of ENSO on the polar stratosphere is related to the delayed thermal response in the
tropics and midlatitudes to ENSO, which persist from winter to summer and spans from the
troposphere to the stratosphere.
Page | 66
372
Decadal variation of El Niño over last three decades causing strengthened
Walker circulation
1
2
1
B.J. Sohn , Sang-Wook Yeh , Hwan-Jin Song
1
2
Seoul National University, Seoul, Korea, Republic of, Hanyang University, Ansan, Korea, Republic of
In order to examine changes in Walker circulation over the recent decades, we analyzed the sea
surface temperature (SST), deep convective activities, upper tropospheric moistening, sea level
pressure (SLP), and effective wind in the boundary layer over the 30-year period from 1979 to 2008.
The analysis showed that the eastern tropical Pacific has undergone cooling while the western Pacific
has undergone warming over the past three decades, causing an increase in the east-west SST
gradient. It is indicated that the tropical atmosphere should have responded to those SST changes;
increased deep convective activities and associated upper tropospheric moistening over the western
Pacific ascending region, increased SLP over the eastern Pacific descending region in contrast to
decreased SLP over the western Pacific ascending region, and enhanced easterly wind in the
boundary layer in response to the SLP change. These variations, recognized from completely
independent data sources, occur in tandem with each other, strongly supporting intensified Walker
circulation over the tropical Pacific Ocean. From the finding that the SST trend was attributed to more
frequent occurrences of central Pacific-type El Niño in recent decades, it is inferred that the decadal
variation of El Niño caused the intensified Walker circulation over the past thirty years. An analysis of
current climate models shows that models do not reproduce well the observation of an intensified
Walker circulation. While some models do indicate an intensification of the Walker circulation many
others indicate the opposite; this is probably due to the current inadequacy of models to reproduce
decadal variations of El Niño.
Page | 67
546
Interdecadal changes in the relationship between Southern China winter-spring
precipitation and ENSO
1
1
2
1
Zhiping Wen , Jiepeng Chen , Renguang Wu , Zesheng Chen
1
2
Department of Atmospheric Sciences, Sun Yat-sen University, Guangzhou, China, Institute of Space
and Earth Information Science and Department of Physics, The Chinese University of Hong Kong,
Hong Kong, China
Winter-spring precipitation in southern China (SC) tends to be higher (lower) than normal in El Niño
(La Niña) years during 1953-1973. The relationship between the SC winter-spring precipitation and El
Niño-Southern Oscillation (ENSO) is weakened during 1974-1994. The present study demonstrates
this interdecadal change and plausible reasons for this interdecadal change are explored. Abovenormal SC rainfall corresponds to warmer sea surface temperature (SST) in the equatorial central
Pacific (ECP) during 1953-1973, and to warmer SST in the eastern South Indian Ocean (SIO) and
cooler SST in the western South Indian Ocean during 1974-1994. There is a pronounced difference in
anomalous atmospheric circulation corresponding to anomalous winter-spring SC rainfall between the
two periods. During 1953-1973, there are two anomalous vertical circulations presenting between
ascent over ECP and ascent over SC, with a joint branch of descent over the western North Pacific
and an anomalous low-level anticyclone accompanying. During 1974-1994, two anomalous vertical
circulations act to link SC rainfall and eastern SIO SST anomalies, with ascent over eastern SIO and
SC and a common branch of descent over the western North Pacific. Present analysis shows that SIO
SST anomalies can contribute to SC winter-spring precipitation variability independently. The
observed change in the relationship between SC winter-spring rainfall and ENSO is likely related to
the increased SST variability in the eastern SIO and the modulation of the Pacific decadal oscillation.
Page | 68
338
Tropical Pacific mean state and ENSO changes: sensitivity to a freshwater flux
and remnant ice sheets at 9.5kyr BP
1,2
2
1
Yihua Luan , Pascale Braconnot , Yongqiang Yu
1
Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), Beijing, China,
2
Laboratoire des Sciences du Climat et de l'Environnement (LSCE/IPSL), Unité mixte CEA-CNRSUVSQ, Paris, France
Using a coupled model IPSL_CM4 to do the control run for the early Holocene and sensitivity
experiments that involves in boundary forcing from melting water flux and remnant ice sheet, we
explore the relative contribution of melting water flux and remnant ice sheet on the mean state and
ENSO variability in the tropical Pacific in the present study.
Both the melting water flux and remnant ice sheets may induce the North Atlantic cooling and ITCZ
shifting southward. Through atmospheric teleconnections and local coupled ocean-atmosphere
feedbacks, anomalous cooling of SST can be found in the eastern equatorial Pacific in the both two
sensitivity experiments. The cold SST and easterly wind anomalies extend to the western Pacific in the
remnant ice sheet experiment. However, in the melt water flux experiment, the anomalous westerly
winds in the subtropical Pacific restrain the development of the easterly wind and SST cooling in the
western Pacific. Both sensitivity experiments simulate weakened SST seasonal cycles in the eastern
equatorial Pacific, closely related to the zonal wind stress anomalies, which are driven by the
precipitation anomalies in the tropical Atlantic.
Compared with the reference run at the early Holocene, the freshwater flux experiment exhibits
enhanced ENSO amplitude probably because of the wind-thermocline coupling process, but the
remnant ice sheet experiment does not show significant change in ENSO. The further analysis show
that all experiments simulate two kinds of El Niño events, e.g., one is the classical eastern Pacific (EP)
El Niño, and another is the central Pacific (CP) El Niño. The freshwater flux forcing does not only
strengthen the El Niño amplitude, but also increase the frequency of EP El Niño events due to the
stronger thermocline feedback than other experiments.
Page | 69
B1.4 - Applications to air quality monitoring
08.07.2013 13:15-14:45, Seehorn
468
Evidence of added values to the modeling system from specific air quality
satellite missions
1,2
2
2
1,2
2
Jean-Luc Attie , Rachid Abida , Laaziz El Amraoui , Emeric Hache , Philippe Ricaud , Vincent-Henri
3
4
5
Peuch , William Lahoz , Johannes Orphal
1
2
Université de Toulouse/CNRS Aérologie, Toulouse, France, Météo-France/CNRS CNRM/GAME,
3
4
5
Toulouse, France, ECMWF, Reading, United Kingdom, NILU, Kjeller, Norway, KIT, Karlsruhe,
Germany
Air quality (AQ) is defined according values of gas and aerosol concentrations as well as deposition at
the surface based on knowledge of human health and environment impacts. For these main reasons,
ozone, nitrogen oxides, aerosols and carbon monoxide are particular scrutinized atmospheric species.
In general, ground based stations measure most of these species, but the surface network is not
enough dense over Europe, in particular over mountainous regions and over sea, leading to
uncertainties to forecast or modeling AQ systems. In addition, there is a lack of observations within the
two to three kilometers layer above the surface, region which significantly impact the surface. The
temporal variability of these species concentration is about one hour because of the emission
variability, the chemical reactions, etc... Geostationary satellite missions are probably the most
adequate platform from space to monitor, via specific instruments, such a species because of their
time revisit (less than one hour) and their ability to view the same location at the Earth surface. By
now, no space missions are really dedicated to AQ, but several are planned or proposed to fulfill this
target (Sentinel-4/EU, GEMS/Korea, Tempo/US, MAGEAQ-G3E/EU). Using satellite data simulator,
chemical modeling and data assimilation, we propose to show results about the added values of
simulated data constraining chemical models. This is done by performing Observing Simulated
System Experiments. These numerical experiments, though representing a very small fraction of the
cost compared to the development of a real test instrument, will allow to justify quantitatively the
mission and instrument requirements (geometry, sensitivity, errors,…).
Page | 70
339
Monitoring air quality: the role of OSSEs in determining the future global
observing system
1,2
2
William Lahoz , T. Pogeqateam
1
2
NILU, Kjeller, Norway, CNRM/GAME, Toulouse, France
The need to monitor air quality is recognized world-wide. This involves, inter alia, measurements of
key pollutants (e.g. ozone and carbon monoxide) in the lowermost troposphere at spatio-temporal
scales relevant to policy makers (temporal frequencies of order less than 1 hour; spatial scales of
order less than 10-15 km). This presentation identifies the role of data assimilation observing system
simulation experiments (OSSEs) in determining the future global observing system to monitor air
quality. Caveats associated with setting up and interpreting OSSEs are discussed. OSSEs performed
within the POGEQA project to assess the added value of planned and proposed geostationary satellite
platforms for monitoring air quality are presented to illustrate the concept.
Page | 71
1254
Probabilstic ensemble forecasting of air quality at city scale
1
1
Sam Erik Walker , Bruce Rolstad Denby
1
NILU - Norwegian Institute for Air Research, Kjeller, Norway
A first version of a probabilistic ensemble based air quality forecasting system for the cities of Oslo
and Rotterdam is presented. The purpose of the system is to provide probabilistic forecasts (up to 3
days) and nowcasts (current and coming 3 hours) of air quality (NO2 and PM10) for the two cities. To
achieve this, a model chain has been established using ECMWF ensemble forecasts as input to a
meteorological downscaling model (TAPM) which in turn provides meteorological fields as input to an
urban and local scale air quality model EPISODE. Additional inputs to the air quality model include
uncertain emissions and regional scale background concentrations provided by the GEMS/MACC
ensemble of models. A total of 50 ensembles are drawn from these three sources as input to the air
quality model. In addition to the main probabilistic forecasts, regularly updated probabilistic nowcasts
are carried out based on assimilation of available air quality observations using a particle filter
approach that reweights the ensemble members. This paper presents the methodology and results of
the application and carries out an assessment of both the 3 day forecasts and the 3 hour short term
assimilated forecasts. In general the ensemble forecasts are under-dispersed for both cities with
around 75 - 80% of the observations falling within the ensemble 95 percentile range. The assimilation
method tends to improve the nowcasts, but only slightly. The forecast system was developed as a
case study in the EU FP7 project UncertWeb. This project was intended to enable web based
interactions and visualisations of uncertain model input and output.
Page | 72
618
Information content and evolution of the air quality network in Santiago de
Chile
1,2
2,3
2
Laura Gallardo , Axel Osses , Adolfo Henríquez
1
2
Universidad de Chile, Santiago, Chile, Center for Climate and Resilience Research, Santiago, Chile,
3
Center for Mathematical Modeling, Santiago, Chile
We use both variational and statistical techniques to assess the evolution of the air quality network of
Santiago, Chile (33.5S, 70.5W, 500 m.a.s.l). We focus on carbon monoxide (CO), a pollutant mainly
linked to gasoline vehicles which acts as a nearly passive tracer at the city scale. We find that both
techniques result in similar spatial clusters of stations responding to the main circulation and emission
patterns of the network. As expected, the Information content of the network has increased since the
late 1980´s. We provide an objective measure of that increase and discuss tools relevant for the
evaluation and planning of air quality networks.
Page | 73
1228
North Atlantic oscillation and pollutants variability in Europe: model analysis
and measurements intercomparison
1
2
1
1
Francesco S.R. Pausata , Luca Pozzoli , Rita Van Dingenen , Elisabetta Vignati , Frank Dentener
1
2
European Commission, Ispra, Italy, 2Eurasia Institute of Earth Sciences, Istanbul Technical
University, Istanbul, Turkey
1
Ozone pollution and particulate matter(PM) represent a serious health and environmental problem.
While ozone pollution is mostly produced by photochemistry in summer,PM is of main concern during
winter. Both pollutants can be influenced not only by local scale processes but also by long range
transport driven by the atmospheric circulation. We study the role of large scale atmospheric
circulation variability in the North Atlantic basin in determining PM and surface ozone concentrations
over Europe.Here, we show, using ground station measurements and a coupled atmospherechemistry model simulation for the period 1980-2005,that with regards to ozone the North Atlantic
Oscillation(NAO) does affect its surface concentrations during all seasons except fall. We find that the
first Principal Component(PC1), computed from the time variation of the sea level pressure(SLP) field,
detects the atmosphere circulation/ozone relationship not only in winter and spring (as the canonical
NAO Index) but also during summer, when the atmospheric circulation weakens and regional
photochemical processes peak.Given the NAO forecasting skill at intraseasonal time scale, the PC1 of
the SLP field could be used as an indicator to identify areas more exposed to forthcoming ozone
pollution events.Finally, our results suggest the increasing baseline ozone in western and northern
Europe during the 1990s could be related to the prevailing positive phase of the NAO in that period.
With regards to PM, our study shows that in winter the NAO modulates surface PM concentrations
accounting in average up to 30% of total PM variability.During positive NAO phases, positive PM
anomalies occur over southern Europe, and negative anomalies in central--northern Europe.A positive
shift of the NAO mean state, hence, leads to an increase in cardiac and respiratory morbidity related to
PM exposure in the Mediterranean countries with up to over 500 more deaths per 10 million people for
a 2000 emission inventory.
Page | 74
PS-1 - Poster session Monday
08.07.2013 14:45-16:15, Foyer
MO-01_A3.1
Analysis of climate variability in Anambra State of Nigeria using 30 years
rainfall and temperature data
1
1
2
Fidelis Okorie , Pat N. Duru , Ifeyinwa C. Okeke
1
Department of Geography and Environmental Management, Imo State University, Owerri, Nigeria,
2
Department of Geography, University of Lagos, Akoka, Lagos, Nigeria
Developing countries especially, those in arid, semi-arid and high rainfall regions, are more vulnerable
to climatic variations and change. Nigeria is one of such developing countries and it is well known that
Nigeria climate has varied in time and space, and it will continue to vary in future. Precipitation has
generally occurred, and is predicted to continue to occur. Likewise, severe weather events and natural
disasters are occurring more frequently, and intensely than expected compared to historical records
(Sumiet et al, 2004). As global temperature continues to increase, these extreme events are predicted
to occur more often and with greater severity (Klein Tank et al, 2005). A lot of variations in rainfall,
particularly have occurred for the different climatic regions and individual locations in Nigeria. In the
southeast, Anambra State for example, droughts have been relatively less persistent, while rainfall is
observed to be increasing and temperature increases steadily with slight decrease over the years
compared with other states, particularly in the northern regions. This study contends that temperature
and rainfall, key weather variables, are the driven forces responsible for climatic variability in Anambra
State, hitherto other regions. Hence this paper tries to analyse variability in climate of the state using
temperature and rainfall indices. The 30 years (1981-2009) climatic data for Anambra State was
acquired from Nigerian Meteorological Agency, Lagos. Results show a lot of variations in the climatic
systems of the state within the period under study. Recommendations were made at the end on how
to adapt to impact of climate variability.
Page | 75
MO-02_A3.1
ENSO parameterization including the hysteresis in response to CO2
concentration changes
1
Masamichi Ohba
1
Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry,
Abiko, Japan
The degree of hysteresis/reversibility of El Niño/Southern Oscillation (ENSO) behavior are examined
by using an air-sea coupled climate model under a simple idealized climate change scenarios where
the atmospheric CO2 concentration is gradually increased to four times the pre-industrial level and
then reduced at a similar rate from several points along this trajectory. While the simulated ENSO
amplitude is evidently reduced as CO2 concentration increase, that in the CO2 decrease phase
exhibits enhanced ENSO activity with the relative El Niño-like warming pattern of sea surface
temperature anomalies. Most of the El Niño-like warming is attributed to a weakened cold water
upwelling in the equatorial eastern Pacific that is due to the reduced vertical ocean temperature
gradient in relation to a lag of subsurface temperature warming relative to the surface temperature
change. Our findings have implications for the parameterization of ENSO variation in simple climate
models and for future climate studies of geoengineering scenarios. From these findings, we also try to
propose a simple ENSO parameterization method for simple climate models. This method relatively
well capture the asymmetry in ENSO amplitude change between the increased and decrease phase of
CO2 concentration.
Page | 76
MO-03_A3.1
Optimal precursors for ENSO events in the Zebiak-Cane model
1
1
2
Hui Xu , Wansuo Duan , Mu Mu
1
2
LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China, Key
Laboratory of Ocean Circulation and Wave, Institute of Oceanology, Chinese Academy of Sciences,
Qingdao, China
Within the frame of Zebiak and Cane model (ZC model), the problem of optimal precursors for ENSO
events is explored by using the approach of conditional nonlinear optimal perturbation (CNOP). For
different optimization time intervals, CNOPs and local CNOPs (LCNOPs) of a climatological annual
cycle are obtained. These CNOPs and LCNOPs have respectively the robust patterns qualitatively,
which are quite different from those of the corresponding linear singular vector (LSV). And the
nonlinear evolutions of CNOPs (LCNOPs) are significantly larger than those of the corresponding
LSVs for the same magnitudes of initial perturbations. This suggests that CNOPs (LCNOPs) tend to
be the initial patterns that evolve into El Nino (La Nina) events most probably. CNOPs (LCNOPs) can
therefore be regarded as the optimal precursors for El Nino (La Nina).The magnitudes of the nonlinear
development of CNOPs (LCNOPs) are highly dependent on the phase of the annual cycle at which
perturbations are applied, and on the duration over which perturbations evolve. However, the spatial
structure of the optimal precursors is insensitive to these factors. The positive (negative) thermocline
depth anomaly of equatorial Pacific is an obvious character of the optimal precursor of an El Nino (a
La Nina) event, i.e., CNOP (LCNOP). A mechanism that optimal precursors develop into ENSO events
is given based on the positive feedback of tropical ocean-atmosphere interaction. Finally, we reveal
theoretically the fact that El Nino is generally stronger than La Nina. The obtained results indicate that
nonlinearity plays an important role in ENSO asymmetry.
Page | 77
MO-04_A3.1
Influences of ENSO teleconnection on the persistence of sea surface
temperature in the tropical Indian Ocean
1
1
Ruiqiang Ding , Jianping Li
1
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
This study confirms a weak spring persistence barrier (SPB) of SSTA in the western tropical Indian
Ocean (WIO), a strong fall persistence barrier (FPB) in the South China Sea (SCS), and the strongest
winter persistence barrier (WPB) in the southeastern tropical Indian Ocean (SEIO). During El Niño
events, a less abrupt sign reversal of SSTA occurs in the WIO during spring, an abrupt reversal occurs
in the SCS during fall, and the most abrupt reversal occurs in the SEIO during winter. The sign
reversal of SSTA implies a rapid decrease in SSTA persistence, which is favorable for the occurrence
of a persistence barrier. The present results indicate that a more abrupt reversal of SSTA sign
generally corresponds to a more prominent persistence barrier. El Niño-induced changes in
atmospheric circulation result in reduced evaporation and suppressed convection. This in turn leads to
the warming over much of the TIO Basin, which is an important mechanism for the abrupt switch in
SSTA, from negative to positive, in the northern SCS and SEIO. The seasonal cycle of the prevailing
surface winds has a strong influence on the timing of the persistence barriers in the TIO.
The Indian Ocean Dipole (IOD) alone can cause a weak WPB in the SEIO. El Niño events cooccurring with positive IOD further strengthen the SEIO WPB. The SEIO WPB appears to be more
strongly influenced by ENSO than by the IOD. In contrast, the WIO SPB and the SCS FPB are
relatively independent of the IOD.
Page | 78
MO-05_A3.1
A combination mode of annual cycle and the El Nino-Southern Oscillation
1
2
2
1
1
Axel Timmermann , Malte Stuecker , Fei-Fei Jin , Karl Stein , Niklas Schneider
1
2
IPRC, SOEST, University of Hawaii, Honolulu, United States, Department of Meteorology, University
of Hawaii, Honolulu, United States
Atmospheric circulation anomalies associated with the interannual El Nino-Southern Oscillation
(ENSO) phenomenon exert global impacts on the climate system . El Nino events are characterised by
positive Sea Surface Temperature (SST) anomalies in the eastern equatorial Pacific, whereas La Nina
events exhibit an anomalously cold sea surface. ENSO is considered an oscillatory instability of the
tropical Pacific coupled ocean-atmosphere system. The boreal winter peak of El Nino events and the
seasonal variance modulation of associated eastern equatorial SST anomalies, often referred to as
phase-locking, document ENSO´s tight interaction with the seasonal cycle. To date there exists no
established theory for ENSO´s synchronisation with the annual cycle. In this study, we show that
seasonal changes in the western tropical Pacific warm pool region interact with El Nino, giving rise to a
near-annual combination climate mode with periods of 10 and 15 months that induces the termination
of El Nino events, thereby controlling ENSO´s seasonal synchronisation and predictability. This new
mode is shown to cause massive shifts of Earth´s largest rainbands, impacting human livelihoods
across the Asia-Pacific region and beyond.
Page | 79
MO-06_A3.1
Contribution of the location and spatial pattern of initial error to uncertainties
in El Niño predictions
1
2
3
2
Yanshan Yu , Mu Mu , Wansuo Duan , Tingting Gong
1
2
School of Mathematical Sciences, Monash University, Melbourne, Australia, Institute of
3
Oceanography, Chinese Academy of Sciences, Qingdao, China, Institute of Atmospheric Physics
(IAP), Chinese Academy of Sciences (CAS), Beijing, China
With the Zebiak-Cane model, the contribution of the location and spatial pattern of initial error in sea
surface temperature anomalies (SSTA) to uncertainty in El Niño predictions is investigated using an
approach based on conditional nonlinear optimal perturbation (CNOP), which seeks to find the initial
error (i.e., the CNOP error) that satisfies a given constraint and that causes the largest prediction error
at the prediction time. The computed CNOP error of SSTA has a dipole pattern in the equatorial
central and eastern Pacific. The initial error from the equatorial central and eastern Pacific tends to
grow more significantly than those from other locations. Because of the contribution of annual mean
states the location of the initial error plays an important role in the error evolution; e.g., the shallow
annual mean thermocline in the eastern Pacific favors feedback between the thermocline and sea
surface temperature. Meanwhile, the specific dipole structure of the initial error is also crucial for
optimal error growth. Even with the same magnitude as the CNOP error, random initial error in the
equatorial central and eastern Pacific does not evolve significantly over time. Initial errors of SSTA
with a similar spatial pattern to the CNOP error (i.e., the dipole pattern of SSTA error) give rise to
larger prediction errors than those without similar spatial pattern do. Consequently, the magnitude of
the prediction error at the prediction time depends on the combined effects of the location and spatial
pattern of the initial error. If additional observation instruments are deployed to observe sea surface
temperature with limited coverage, they should preferentially be deployed in the equatorial central and
eastern Pacific.
Page | 80
MO-07_A3.1
Change of the interannual variation patterns of winter surface temperature in
China
1
Maoqiu Jian
1
Department of Atmospheric Sciences, Sun Yat-sen University, Guangzhou, China
Under the climate change background of global warming, a quick warming of winter near surface
temperature occurred in 1987 in China in recent fifty years. Based on the observed winter near surface
temperature(WNST) data of 1961 to 2009 and the NCEP/NCAR reanalysis data, this study examines
the change feature of interannual variation patterns of WNST in China and the associated change of
East Asian winter monsoon(EAWM) activities along with the quick warming in East Asia. The observed
evidence shows there really exists an interdecadal change in the spatial pattern of the WNST
interannual variation. During the twenty-five years period before 1987, the dominant interannual
variation pattern of WNST in China is a nationwide inphase mode except the Tibetan Plateau area.
However, during the period after 1987, there two dominant interannual modes of WNST, one is an
eastern inphase mode located mainly in the eastern part of China, the other inphase mode covers the
central and western parts of China. The change of interannual variation patterns of WNST in China is
associated with the interdecadal change of East Asian winter monsoon activities during the past fifty
years, which is also linked to the global warming. The mechanisms of the EAWM´s influence in the
WNST are also discussed.
Page | 81
MO-08_A3.1
Searching for periodicities in 100 year record of atmospheric transmission at
Davos
1
1
Christoph Wehrli , Daniel Lachat
1
PMOD/WRC, Davos Dorf, Switzerland
The longest stationary record of direct solar irradiance measurements carried out since 1909 to
present at the PMOD has been evaluated in terms of apparent atmospheric transmission and
analysed for secular and decadal trends corresponding to periods of Dimming and Brightening
observed in global radiation. Several small, but statistically significant decadal trends reflecting the
Dimming and Brightening epochs in global radiation were identified and shown to be mostly due to
apparent aerosol transmission.
Here we will examine this outstanding time-series of atmospheric transmission looking for (quasi)
periodic patterns and possible relations to QBO and ENSO indices.
Page | 82
MO-09_A3.1
The long-term cooling of cold tongue mode and its impacts on ENSO regimes
1
2
1
1
1
1
3
Jianping Li , Wenjun Zhang , Yang Li , Juan Feng , Fei Xie , Muhammad Afzaal , Feifei Jin , Cheng
1
4
Sun , Xia Zhao
1
2
Institute of Atmospheric Physics, BeiJing, China, Nanjing University of Information Science and
3
4
Technology, Nanjing, China, University of Hawaii, Hawaii, United States, Institute of Oceanology,
Qingdao, China
The analyses from both the observational sea surface temperature (SST) datasets and outputs of
CMIP (CMIP3 and CMIP5) models show that there is a Pacific cold tongue mode (CTM) in topical
Pacific SST variability. The CTM is the second EOF mode of SST variability over tropical Pacific that
represents out-of-phase relationship in SST variability between the Pacific cold tongue region and
elsewhere of the tropical and subtropical Pacific. Positive CTM is characterized by the cold SST
anomalies in the Pacific cold tongue region and the warm SST anomalies in the rest of the tropical and
subtropical Pacific, and vice versa. In fact, this is a coupled air-sea mode. Long-term variability of the
CTM experiences a long-term strengthening, which is featured by cooling in the Pacific cold tongue
and warming elsewhere in the tropical and subtropical Pacific. The CTM is also shown in the CMIP
coupled models in a preindustrial scenario with no forcing attributed to global warming but shows an
interannual variability. Results from observations and models suggest that the long-term strengthening
of the CTM is very likely caused by global warming. Analysis further suggests that the long-term
cooling of the CTM can significantly modulate ENSO regimes. During last 140 years there are three
types of tropical Pacific SST warming or cooling event, respectively, i.e., typical El Niño, cold tongue
(CT) El Niño, and central Pacific (CP) warming, typical La Niña, CT La Niña and basin-wide La Niña
(BLN). Consequently, in the case of warming background in the future the CP El Niño and CT La Niña
will occurs more frequently. In the case of warming background CP warming event and CT La Niña will
occurs more frequently in the future.
Page | 83
MO-10_A3.1
Long-term prognosis of ENSO dynamics: prognosis of critical transitions in
models of ENSO
1
1
1
Evgeny Loskutov , Dmitry Mukhin , Alexander Feigin
1
Institute of Applied Physics of the RAS, Nizhny Novgorod, Russian Federation
We consider the problem of prognosis of critical transitions in models describing the ENSO dynamics.
For this purpose the approach based on construction of parameterized stochastic models of discrete
evolution operator is proposed [1]. In this approach, the key (“robust”) dynamic properties of the
system evolution can be described by a few variables, while other features may be considered as a
stochastic disturbance. Stochastic models of this sort are of the form of random dynamical systems;
they present a necessary and important step towards reconstructing the observed systems when their
adequate first-principle mathematical models are either unknown or subjected to further verification.
We construct stochastic model of evolution operator of unknown system by virtue of scalar time series
generated by the system. The model operator includes deterministic as well as stochastic terms; both
of them supposed to be inhomogeneous in the model state space and are parameterized by artificial
neuron networks.
The ability of the approach to provide prognosis for times greater than observation time interval is
demonstrated on time series taken from the intermediate complexity ENSO models. Slow drifts of
control parameters were introduced to these ENSO models to simulate slowly changing external
conditions of the system. Prognosis of qualitative behavior from time series is shown, including
prognosis of PDFs evolution, spectral density evolution and prognosis of main qualitative transitions
Reference:
1. Molkov Ya.I., Loskutov E.M., Mukhin D.N., and Feigin A.M.,Random dynamical models from time
series, Phys.Rev.E 85, 036216, 2012.
Page | 84
MO-11_A3.1
ENSO prediction by the analysis of observed variability of SST
1
1
1
1
Dmitry Mukhin , Evgeny Loskutov , Andrey Gavrilov , Anna Mukhina
1
Institute of Applied Physics of RAS, Nizhny Novgorod, Russian Federation
In this report the empirical methodology for prediction of ENSO dynamics is suggested. We construct
the dynamical models of SST field patterns connected with ENSO phenomenon, from observed time
series. The model is based on artificial neural network (ANN) parameterization and has a form of
discrete stochastic evolution operator mapping some sequence of system´s state on the next one. It
operates in space of spatial orthogonal functions constructed from SST field, which have largest
correlations with an index of ENSO we want to predict. The most important point of the method is
finding the optimal structural parameters of the model such as dimension of variables vector, i.e.
number of principal components used for modeling, number of states used for prediction, and number
of neurons determining quality of approximation. Actually, we need to solve the model selection
problem, i.e. we want to obtain a model of optimal complexity in relation to analyzed time series. We
use MDL [1] approach for this purpose: the model providing most data compression is chosen. The
method is applied to time series of SST fields taken from IRI datasets [2].
References:
1. Molkov, Ya.I., D.N. Mukhin, E.M. Loskutov, A.M. Feigin, and G.A. Fidelin, Using the minimum
description length principle for global reconstruction of dynamic systems from noisy time series. Phys.
Rev. E, 80, 046207, 2009.
2. IRI/LDEO Climate Data Library (http://iridl.ldeo.columbia.edu/)
Page | 85
MO-12_A4.1
The use of the National Ice Center (NIC) charts as a large-scale validation proxy
1
1
2
1
Penelope Wagner , Cathleen Geiger , Sean Helfrich , Tracy DeLiberty
1
2
Geography, University of Delaware, Newark, United States, National Ice Center, Suitland, United
States
The sea ice edge is difficult to survey due to its amorphous structure and unclear demarcation of the
sea ice edge boundary from different points of view in the science and operational communities. It is
an integral component of both climate models and forecast projections, as well as ice charting analysis
for navigational purposes. It can also be used as an indicator of the changing climate because it is
highly responsive to temperature variations. The National Ice Center (NIC) creates sea ice products
that aid in navigation, including information on sea ice: concentration, edge location, thickness, and
extent. The sea ice edges are outlined for both products; however, cartography techniques differ
considerably. A clear understanding of NIC ice chart precision will aid in these best practice
developments for this data. By assessing the continuity of NIC charts, the quality can be appraised of
how well these datasets can be used as a dependant variable for a large-scale validation proxy. A
technique was developed to quantify the differences between both NIC products with the use of
Antarctic sea ice charts due to the ease of measurements for a 2-D geographic problem. NIC sea ice
charts from 2004-2011 were evaluated with the use of hierarchal statistical applications. The charts
demonstrated normal distributions which are temporally dependent, and show that differences are
insignificant at the 95% level for each statistical test performed. Results obtained from the NIC charts
for an observed time series of the NIC daily and bi-weekly differences express the largest deviation in
the maximum and minimum values during February-March, August, and December at approximately
~150 - 200km. The highest percent difference is shown during the summer months in February and
December at ~6%, whereas the August difference is at ~5.0% - 5.5% for maximum sea ice edge
location coordinates.
Page | 86
MO-13_A4.1
Sea ice motion over minute-scale time intervals
1
Andreas Kääb
1
Department of Geosciences, University of Oslo, Oslo, Norway
Using spaceborne remote sensing data sea ice motion is typically tracked over time intervals of hours
to days. In this study, we track sea ice motion over a time period of about one minute, which is the
typical time lapse between the two or more images that form a stereo data set in spaceborne, alongtrack optical-stereo mapping. Using this novel approach, we measure and visualize for the first time
the almost complete two-dimensional minute-scale surface velocity fields over several thousands of
square-kilometers of sea ice cover. We present the types of short time-delay imagery suitable for the
measurements and discuss application examples in the Arctic and Antarctica, using a range of high
and medium resolution imagery. The methodology and results of the novel approach are hoped to be
usefull to understand a number of processes involved in sea ice drift, such as wind impact and
interaction of ice floes with each other and with obstacles.
Page | 87
MO-14_A4.1
Impact of resolution error on sea ice thickness accuracy
1
2
3
Cathleen Geiger , Jacqueline Richter-Menge , Jesse P. Samluk
1
2
Geography, University of Delaware, Newark, United States, Terrestrial and Cryospheric Sciences
3
Branch, USACE CRREL, Hanover, United States, Department of Electrical and Computer
Engineering, University of Delaware, Newark, United States
Findings from sea ice thickness retrievals using electromagnetic induction (EM) devices are influenced
by error sources which cannot be corrected by calibration alone. These include (1) the intrusion of
saline water into ridges, (2) geo-locations errors, (3) resolution error, and others. This paper touches
on error (1), statistically quantifies (2), but mainly explores (3) because of its impact on all
measurement systems and the fact that it has received little attention within the sea ice community.
Thickness profiles by coincident helicopter-borne (Airborne EM) and hand-held (Ground EM) devices
are one of the few existing sea ice thickness instruments capable of resolving this phenomenon mainly
due to their abilities to oversample. A comparison using over 1000 coincident measurements, across
three orders of magnitude (centimeters to dekameters), shows considerable differences in thickness
distribution. We attribute these differences to resolution caused by instrument footprint size even
though there is little change (12.4%) in integrated thickness as a volume proxy per unit length. We
explore a power-law parameterizing for resolution error with resulting slopes varying from 0.4 to 0.7
depending on the shape of the smoothing function and the resolution of the original data acquisitions.
These findings strongly indicate a need for more study on the topic of resolution error to improve the
accuracy of sea ice thickness measurements in support of regional and climate forecasting, socioeconomic human activities, and monitoring of polar ecosystems.
Page | 88
MO-15_A4.1
Variability in Barents Sea and Svalbard area ice extent revisited
1
Nicholas Hughes
1
Norwegian Meteorological Institute, Tromsø, Norway
The spring maximum sea ice extent in the Barents Sea and around the Svalbard archipelago is known
th
from previous studies to have declined throughout the 20 Century but with significant decadal
variations. Data used in the studies was published by the WCRP Arctic Climate System Study
(ACSYS), and in later years was predominantly based on sea ice charts produced by the Norwegian
Meteorological Institute from the analysis of a combination of different satellite sensors including
passive microwave and optical. The generation of a further 10 years of ice charts, with increasing
detail due to utilisation of active microwave satellite data from Radarsat-1 and -2, enables this paper to
provide a new assessment of sea ice extents in the area to see if the long-term trends and cyclicity
observed in the sea ice extent are still valid and can be used to provide the basis for a forecast of
future climate conditions. Notable extreme minimums in sea ice extent in the winters of 2006 and 2012
also suggest that the sea ice regime of the region may be entering a new phase. Further study of
changes in the sea ice extent and predictable patterns are of particular interest with the increasing
maritime activity in the Barents Sea region.
Page | 89
MO-16_A4.1
SMOS derived sea ice thickness in the Arctic and its validation
1
1
1
2
3
Xiangshan Tian-Kunze , Lars Kaleschke , Nina Maass , Marko Maekynen , Thomas Krumpen , Stefan
3
4
1
5
Hendricks , Christian Haas , Nuno Serra , Matthias Drusch
1
2
Institute of Oceanography, ZMAW, University of Hamburg, Hamburg, Germany, Finnish
3
Meteorological Institute, Helsinki, Finland, Alfred Wegener Institute for Polar and Marine Research,
4
Bremerhaven, Germany, Department of Earth and Space Science and Engineering, York University,
5
Toronto, Canada, ESTEC, ESA, Noordwijk, Netherlands
A forward sea ice emissivity model coupled with a thermal dynamic model is used to calculate sea ice
thickness in the Arctic based on the brightness temperatures measured by the Microwave Imaging
Radiometer using Aperture Synthesis (MIRAS) on board ESA´s Soil Moisture and Ocean Salinity
(SMOS) mission. SMOS measures brightness temperatures in full polarization and diverse incidence
angles at L-band. For our application we use the intensity averaged in the incidence angles from 0° to
40°, in which the intensity remains almost constant.
In a previous study (Kaleschke et al., 2012) it is shown that L-band radiometry can be used to detect
thin sea ice thickness up to half a meter under cold conditions. However, the semi-empirical retrieval
algorithm used in the study made strong simplifications assuming constant ice temperature and ice
salinity as well as closed ice cover. This can cause significant errors. Therefore, we improved the
retrieval algorithm using a forward model including ice salinity, ice temperature and ice concentration.
Ice concentration is measured by passive microwave sensors. Since ice temperature and ice salinity
are functions of ice thickness, we use the ice thickness from semi-empirical retrieval algorithm as initial
guess of ice thickness. With this first guess ice temperature is calculated using a thermal dynamic
model with surface air temperature from atmospheric reanalysis as input. Sea ice salinity is estimated
from Sea Surface Salinity (SSS) climatology and initial ice thickness with Ryvlin equation. The whole
process is repeated until the convergence of the ice thickness is achieved.
SMOS sea ice thickness data are then compared and validated with MODIS-based ice thickness in the
Kara Sea and EM-bird ice thickness measurements in the Laptev Sea. The uncertainty of SMOS sea
ice thickness is estimated based on the validation.
Page | 90
MO-17_A4.1
Errors analysis of the retrieved sea ice thickness from satellite based radar
altimeter and upward looking sonar
1
2
3
4
5
6
Vera Djepa , Stein Sandven. , Eero Rinne , Peter Wadhams , Stefan Kern , Henriette Skourup ,
7
Marko Makynen
1
2
DAMTP, University of Cambridge, Cambridge, United Kingdom, Polar Environment Remote Sensing,
3
4
Bergen, Norway, Finnish Meteorological Institute, Marine Research, Helsinki, Finland, University of
5
6
Cambridge, Cambridge, United Kingdom, University of Hamburg, Hamburg, Germany, DTU Space
7
National Space Institute Geodynamics, Kgs. Lyngby, Denmark, Finnish Meteorological Institute,
Helsinki, Finland
Sea Ice Thickness (SIT) is an important climate variable and accurate records of SIT are required for
assessment of climate change impact in the Polar regions and improved weather and climate forecast.
The uncertainties,contributing to the retrieved SIT and freeboard from the Radar Altimeters on board
ERS-1/2 and ENVISAT satellites are analysed, using collocated "Round Robin Data Package" (RRDP)
of freeboard, SIT and sea ice draft, derived from the Upward Looking Sonar (ULS) and satellite
observations. The RRDP exercise is a part of the Sea Ice Climate Change Initiative (SICCI), funded by
European Space Agency (ESA).
In this paper we analyse the factors contributing to the uncertainty of the SIT retrieved from the
satellite based Radar Altimeter and validate the retrieved SIT and freeboard, using collocated ULS
observations.
The impact of snow on the derived SIT from the Radar Altimeter on board ENVISAT will be
investigated using data from Warren climatology, NASA´s ICEbridge snow radar and combined
airborne laser/radar altimetry. The main algorithms for retrieval of freeboard, SIT and sea ice draft and
corresponding errors will be compared and results from uncertainty analyses will be provided using the
RRDP data base of collocated satellite, airborne and sonar data.
The resulting estimate of the accuracy of the retrieved SIT from satellite and sonar observations with
corresponding uncertainties analyses will have fundamental application in long term geophysical
analyses of climate change impacts in the Arctic, processing of satellite altimeter data and model
forecasts.
Page | 91
MO-18_A4.1
Essential climate variables for sea ice observed from satellites
1
Stein Sandven
1
Nansen Environmental and Remote Sensing Center, Bergen, Norway
The European Space Agency has launched the Climate Change Initiative (CCI), which aims to provide
long-term satellite-based data for climate research. CGOS has defined a set essential climate
variables (ECV) that can only be quantified on global scale by use of satellite observations, and sea
ice is one of these variables. There are more than three decades of passive microwave data for
retrieval of ice concentration and two decades of radar altimeter data for ice thickness estimation. It is
a requirement from GCOS to provide homogeneous and quality-controlled data sets on climate
variables. The ESA CCI sea ice project is focussed on sea ice concentration (SIC) and sea ice
thickness (SIT), but there are other sea ice variables of importance for climate research such as ice
drift, leads, polynyas, melt ponds, snow thickness, surface temperature and others, but these variables
are not yet defined as sea ice ECVs. In order to provide the “best algorithms” for retrieval of SIC and
SIT data sets, an algorithm intercomparison exercise is conducted, where the retrieval methods are
analyzed for different ice conditions. One task is to determine the error sources in the data processing
chain and estimate the total error of the ECV data set. After the ECV data sets are produced a
validation study will be conducted where independent data sets form other satellite data, airborne
surveys and in situ observations are used. The sea ice ECVs will be important for validation of climate
models in the polar regions, where sea ice is a sensitive climate variable. Sea ice ECVs are also
important for many other users groups, such as operational sea ice services, marine transportation, oil
and gas exploration, marine ecosystem research, fishery management, and protection of the
environment in the polar regions.
Page | 92
MO-19_A4.1
Satellite analysis of Arctic and Antarctic sea ice extent in the years 1982 to
2012
1
2
2
Cristina Schultz , Fernanda Casagrande , Catarina M. Cecilio
1
Centre for Weather Prediction and Climate Studies, National Institute for Space Reseach, Sao Paulo,
2
Brazil, National Institute for Space Reseach, Sao Jose dos Campos, Brazil
Sea Ice is a key element of the cryosphere, mainly due to its global influence on the heat and mass
transfer processes. Its capacity of isolation restricts the energy and mass transfers between the ocean
and atmosphere, influencing salinity and consequently the density of the upper layers of the ocean,
which can influence the ocean circulation and formation of deep waters. During the last decades,
Arctic and Antarctic sea ices have presented very distinct trends in relation to sea ice cover. The Arctic
sea ice has been decreasing in an accelerated rate, in contrast with the Antarctic sea ice, that
presents a tendency of increase in almost all regions. In this study, variations of the extent of sea ice
in the Arctic and in Antarctica were analyzed using satellite-derived data from the NOAA Optimum
Interpolation (OI) SST, a data set that includes sea ice concentration at the resolution of 1 degree of
latitude and longitude. The results show a trend of increasing sea ice extent in Antarctica, even more
in the Ross and Weddell Seas, and a trend of decreasing sea ice extent in the Bellingshausen and
Amundsen Seas. In the years 2006 and 2012 record maximum extent were observed in the Antarctic
sea ice. In contrast, Arctic sea ice presented its minimums in the years 2007 and 2012, the later
2
reaching the lower limit of 3.5 million km . These studies are important given sea ice acts not only as a
climate change indicator but also as an amplifier for these changes on a global scale.
Page | 93
MO-20_A6.1
Climate feedbacks of the Greenland ice sheet as simulated by EC-Earth
coupled with the PISM ice sheet model
1
1
1
1
Marianne Sloth Madsen , Shuting Yang , Synne H. Svendsen , Gudfinna Adalgeirsdottir , Christian
1
Rodehacke
1
Danish Meteorological Institute (DMI), Copenhagen Ø, Denmark
The role of the Greenland ice sheet in a warmer climate is investigated using a recently developed
global climate model system which includes the global climate model EC-Earth coupled with the
Parallel Ice Sheet Model (PISM). To establish a physically sound coupling, the EC-Earth surface
physical parameterization has been adapted to the land ice surface with e.g. improved snow albedo
parameterization for glaciated regions. In the coupled system, the surface mass balance results from
precipitation, evaporation, and melting of snow and ice and is calculated inside EC-Earth to ensure
conservation of mass and energy. Surface mass balance and surface temperature are used to force
PISM which provides glacier mask, basal melt and ice discharge to be used by EC-Earth.
A spin-up run using EC-Earth pre-industrial climate as a constant forcing for PISM is used to prepare
an initial state in equilibrium with the EC-Earth climate. The coupled EC-Earth/PISM system is then
integrated under pre-industrial conditions until quasi-stationarity is reached. To study the interaction of
the Greenland ice sheet, an experiment with an idealized 1% CO2 increase pr year from pre-industrial
concentrations to 4 times CO2 is performed for 300 years (i.e. stabilized at 4xCO2 for 140 years). The
evolution of the Greenland ice sheet in the 4xCO2 scenario and its impacts on the climate system are
investigated and compared with the preindustrial control simulation. The freshwater flux to the North
Atlantic basin from surface melting and ice discharge of the Greenland ice sheet and its role in
changing the strength of the North Atlantic Meridional Overturning Circulation are analyzed. The
regional climate changes associated with the dynamic and thermodynamic effect of the Greenland ice
sheet change are also quantified.
Page | 94
MO-21_A6.1
Modelling temperate ice dynamics using different parametrizations of the flow
rate factor
1
2
2
3
2
Martin Rückamp , Jaime Otero , Francisco J. Navarro , Angelika Humbert , Javier J. Lapazaran , Ralf
4
Müller
1
2
University of Hamburg, Hamburg, Germany, Matemática Aplicada a las Tecnologías de la
3
Información, Universidad Politécnica de Madrid, Madrid, Spain, Alfred Wegener Institute for Polar and
4
Marine Research, Bremerhaven, Germany, Mechanical and Process Engineering, University of
Kaiserslautern, Kaiserslautern, Germany
The dynamics and prognostic studies of glaciers, ice caps and ice sheets is linked to the uncertainties
in the description of the rheology of temperate ice. Besides the limited knowledge on the rheology of
temperate ice, the available experimentally-based relationship for the flow rate factor is only valid for
water contents up to 1% (Duval, 1977). However, actual water contents found in temperate and
polythermal glaciers are sometimes substantially larger (up to 5%, Bradford and Harper, 2005). The
advantage of deriving the water content by solving numerically for the water content is leveled out by
the disadvantage of using a flow rate factor with a restricted validity range. We present a two-fold
study which might lead in the future to an entirely new constitutive relation for temperate ice.
If a relationship between rate factor and water content spanning the entire range of water content
found in temperate ice were available, it would be possible to infer the spatial distribution of the rate
factor, which would substantially improve the modeling of glacier dynamics. We use an inverse
method to infer, from glacier geometry and surface velocities, the spatial distribution of the rate factor.
This distribution is compared with the distribution of water content obtained from GPR data to obtain a
rate factor-water content relationship.
Furthermore, we have implemented the enthalpy method (according to Aschwanden et al., 2012) in a
FE full-Stokes flow model. We run a sensitivity analysis to demonstrate the effect on the flow dynamics
using different approaches for temperate ice. The comparison includes a simply cold-ice scheme and
the temperate-ice scheme (enthalpy) together with different relationships of the flow rate factor
(classical Arrhenius-relationship, Duval-relationship, Duval-relationship extrapolated to larger water
content values, relationship obtained from inverse modeling).
Page | 95
MO-22_A6.1
Percolation effects in ice sheet water dynamics
1
Dmitry Iudin
1
Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS), Nizhny Novgorod,
Russian Federation
Ice mechanical properties, and hence the response of glaciers to external driving, depend strongly on
the presence of liquid water at ice-grain boundaries. The propagation velocities of radar and seismic
waves are also highly sensitive to this water. We present a percolation-based approximation in which
we model water inclusions within solid ice. It is suggested that due to formation of long-range
connectivity in random systems of water inclusions, englacial and subglacial water systems are
coupled together in ice sheet and therefore should be modelled as interdependent networks. A
fundamental property of interdependent networks is that failure of nodes in one network may lead to
failure of dependent nodes in other networks. This may happen recursively and can lead to a cascade
of failures. We show that a failure of a very small fraction of nodes in one network may lead to the
complete fragmentation of a system of interdependent water networks.
Page | 96
MO-23_B1.4
Effects of biomass burnings on diurnal variation and vertical distribution of
carbonaceous compositions at the southern of Thailand
1
Siwatt Pongpiachan
1
School of Social and Environmental Development, National Institute of Development Administration
(NIDA), Bangkok, Thailand
Carbonaceous compositions, water-soluble ionic species and trace gaseous species were identified
and quantified in Hat-Yai city, Thailand. All samples were collected every three hours consecutively
from 21:00 h December 17th to 21:00 h December 20th at Site-1 (30 m agl), Site-2 (60 m agl) and
site-3 (125 m agl). The averaged concentration of OC was significantly higher at the Site-1 than those
detected at Site-2 and Site-3 suggesting that anthropogenic activities at ground level might play a
major role in governing air quality at ground level. The altitude-decreasing pattern of correlation
coefficients between OC and EC was detected during the observatory period. This can be explained
by the difference of emission sources coupled with dilution effects occurred at higher altitude due to
relatively strong wind speed at Site-3. The morning peak of carbonaceous compositions observed
during the sampling period of 06:00-09:00 emphasized the main contribution of traffic emissions on
OC/EC contents in Hat-Yai city. Since Site-3 averaged OC/EC ratio was significantly three times
higher than those of Site-1 and Site-2, it seems rationale to assume that either aged maritime aerosols
from long-range transportation and/or biomass burning particles overwhelmed carbonaceous aerosols
at the top of building. Whilst hierarchical cluster analysis and Pearson correlation analysis show some
considerable influences of night-time tourism activities on carbonaceous contents at ground level,
principal component analysis highlights the impacts of maritime aerosols, biomass burning and
possibly agricultural waster burning particles at higher atmospheric layer.
Page | 97
MO-24_B1.4
A climatological study of the relations between AOD-α and PMx for northcentral Spain
1
1
1
1
Yasmine S. Bennouna , Victoria E. Cachorro , Carlos Toledano , Benjamin Torres , María Ángeles
1
1
1
1
Burgos , Ramiro González , David Fuertes , Angel M. de Frutos
1
Atmospheric Optics Group (GOA), University of Valladolid, Valladolid, Spain
This work investigates the relations existing between columnar and surface aerosol properties using
long records of Aerosol Optical Depth (AOD) (with associated Ångström coefficient α) and Particulate
Matter (PMx) parameters for two representative regions of the Iberian Peninsula. In a recent study,
AOD-PMx correlations have been analyzed during a two year period (2006-2007) for a coastal southwestern site: the ESAt station of El Arenosillo. Here, new results focusing on the north-central area of
Spain are presented, where AERONET and EMEP networks have nearby sites, Palencia and
Peñausende respectively, both providing measurements for a period spanning from 2003 to 2011. The
EMEP station reports simultaneously PM10 and PM2.5 on a daily basis. AERONET gives
measurements of the AOD and α at different wavelengths every 15 minutes during daytime. In total
1813 days of coinciding data are obtained for the selected period of study.
On average, the region is characterized by a daily AOD(440 nm) of 0.15±0.10, α (440-870 nm)
1.29±0.35, PM10 11±9.55 µg.m-3 and PM2.5 6.60±4.88 µg.m-3, typical of a clean continental
background. The seasonal pattern corresponds to higher AOD values in spring and summer (max
0.19), and conversely lower values during fall and winter (min 0.09). The PMx annual cycle presents a
bimodal shape with two maximum, one in spring and one in summer, respectively 12.24 µg.m-3 and
15.60 µg.m-3 for PM10.
This climatological seasonal cycle and year-to-year variability of the AOD are examined in relation with
those of PMx. On the other hand, α is analyzed in relation with the seasonal variations of PM2.5/PM10
ratio. The long-term trends of these parameters are also calculated and compared. The level of
correlation between surface and column parameters (R=0.52 for daily AOD-PM10) is also studied as a
function of airmass transport, by means of a cluster analysis using HYSPLIT back trajectories.
Page | 98
MO-25_B1.4
Sensitivity of meteorological input to regional air quality modeling in Pearl
River Delta region, China
1
1
1
1
2
Qi Fan , Yiming Liu , Xuemei Wang , Jing Lan , Yerong Feng
1
2
Department of Atmospheric Science, Sun Yat-sen University, Guangzhou, China, Guangzhou
Central Meteorological Observatory, Guangzhou, China
As one of the three large economic regions of China, the regional air pollution, in which the primary is
aerosol pollution, is serious over Pearl River Delta (PRD) region, China. This study focuses on the
influences of meteorological inputs on air concentrations, with the simulations by Models-3/CMAQ
system on typical air pollution episodes over PRD region. In March 2012, three air pollution episodes
were occurred over PRD, the spatial distributions of air pollutants are circular around Guangzhou and
Foshan cities. The primary pollutants are particulate matter and ozone. In these three episodes, two
air pollution episodes induced low visibility with high relatively humidity. The primary second aerosols
are sulfate and nitrate. Two WRF simulations are conducted to provide the meteorological inputs for
air quality modeling system. One is simulated with FDDA method and another is without FDDA
method. The results show that comparing with the observations from local meteorological bureau, the
temperature, wind speed and wind direction simulations were improved when using FDDA method in
WRF model, the improvements of relative humidity results were minor. With the simulations by WRF
model with FDDA method, the temporal variations of surface concentrations SO2, NO2, O3 and PM2.5
are captured well by CMAQ model. Relatively poor performance is found in the simulated maximum
concentrations of all pollutants, the CMAQ systematically under-predict the mass concentrations.
Comparing the air concentration results by CMAQ model with two different meteorological inputs, no
matter the temporal variation or the spatial distribution of various air pollutants, the results with FDDA
method were better than without FDDA. But the CMAQ model still under estimated the air
concentrations even with the meteorological inputs with FDDA method. The systematically underprediction should be caused by the uncertain of emissions.
Page | 99
MO-26_B1.4
Fine particles and ozone air quality trends in the metropolitan area of Rio de
Janeiro, Brazil
1
1
2
2
Adriana Gioda , Luciana Ventura , Igor Lima , Aderval Luna
1
2
PUC-Rio, Rio de Janeiro, Brazil, UERJ, Rio de Janeiro, Brazil
This work presents an analysis and evaluation of the levels of atmospheric pollution in the Rio de
Janeiro metropolitan region, regarding ozone (O3) and fine particle (PM2.5) concentrations. The
monitoring of these parameters is of utmost importance, due to the fact that both affect the human
health and the environment. Furthermore, Rio de Janeiro will host several international events that will
certainly impact the air quality of the city. Therefore, it is essential to possess measurements prior to
these events. PM2.5 samples were collected during 24 h every six days from several sites of the
metropolitan area of Rio de Janeiro in 2011-2012 using a high-volume sampler. Ozone was
continuously measured in automatic monitoring stations. Meteorological parameters were obtained
from automatic stations near the sampling sites. Particle mass was determined by Gravimetry. The
-3
average PM2.5 concentrations exceeded the suggested annual limit of the WHO (10 µg m ) in most of
-3
the monitored sites. The annual average ozone concentrations ranged from 16 to 45 µg m . Hourly
-3
ozone averages exceeded Brazilian guidelines (160 µg m hourly). The influences of sources both
industrial and from traffic are clearly observed in the levels found at each sampling site. The
relationship between the effects of temperature, relative humidity, wind speed and direction in particle
and ozone concentrations was examined using a Principal Component Analysis (PCA) for the sites
and seasons. The results for each sampling point and season presented different principal component
factors, and showed that changes in meteorological conditions exert a marked influence on air quality.
Page | 100
MO-27_B3.2
Variations in trace gases over the central Himalayas: upslope-downslope
mountain winds and boundary layer dynamics
1
1
1
1
2
Tapaswini Sarangi , Manish Naja , Narendra Ojha , Rajesh Kumar , Shyam Lal , Harish C. Chandola
1
2
3
Atmospheric Science Division, ARIES, Nainital, India, PRL, Ahmedabad, India, Department of
Physics, Kumaun University, Nainital, India
3
Trace gases play vital roles in the tropospheric chemistry, air quality degradation and climate change.
Despite this, measurements of the key trace gases are sparse over the Indian region, particularly over
the Northern India including Indo-Gangetic Plain (IGP), where elevated levels of pollution loadings has
been observed in different satellite based studies. In view of this, measurements of ozone and related
trace gases along with various weather parameters have been made at a high altitude site (Nainital;
o
o
29.37 N, 79.45 E, 1958 m amsl) in the central Himalayas. This site is located just north of the IGP
region and topography is complex around the site.
Diurnal variations in ozone do not show a daytime build up, indicating that photochemistry plays only a
minor role in ozone variations at Nainital. While, in contrast, CO and NOy generally show higher levels
during daytime and lower levels during nighttime. WRF model has been used to simulate the variability
in vertical wind component and boundary layer height. It is shown that the diurnal variations in trace
gases are mainly governed by the dynamical processes including upslope downslope mountain winds
and boundary layer evolution and associated convective mixing. Seasonal variations in ozone, CO
and NOy at Nainital are characterized by spring maxima and summer-monsoon minima. This
seasonality is found in good agreement with the variability of weather parameters. A correlation
analysis using simultaneous ozone observations at Nainital and a nearby low altitude site in the IGP
indicates the major role of boundary layer dynamics in influencing the air quality of the Himalayas. The
correlation among different species is used to gain insight into the sources of these species along with
transport and chemical characteristics of air masses.
Page | 101
MO-28_B3.2
Interactions between the patchy snow cover and convection over late-winter
Tibetan Plateau
1
2
3
Kenichi Ueno , Toshio Koike , Xiangde Xu
1
2
3
University of Tsukuba, Tsukuba, Japan, Tokyo University, Tokyo, Japan, Chinese Academy of
Meteorological Sciences, Beijing, China
Snow cover in the central Tibetan Plateau (TP) is shallow and coexisted with snow-free areas,
producing large surface temperature heterogeneity under strong insolation, and local albedo is
strongly determined by the patchiness of the snow cover (e.g., Ueno et al., 2007, AAAR Vol. 39).
However, land-atmosphere interaction processes based on the observational data in non-monsoon
season have no fully investigated. The one-dimensional structure of a daytime planetary boundary
layer (PBL) with shallow cloud development was captured by intensive sonde observation during the
late winter season at the central TP, and its relationship to patchy snow cover conditions was revealed
(Ueno et al., 2012, JMSJ, Vol. 90C). The diurnal change of potential temperature was evident in the
atmosphere up to 1 km above ground, indicating PBL development, and frequent cloud formation in
the afternoon and night over the PBL was confirmed by the increase of relative humidity in the sonde
data profile and abrupt decrease of brightness temperature in the satellite images. Day-to-day
changes of PBL and nighttime stable layer developments were dependent on the speed of the subtropical jet stream prevailing 5 km above the surface and the changing of snow cover conditions after
snowfall events. Numerical simulations confirmed that the increase of land-surface albedo, imitating
the continuous snow covers, could suppress the PBL and cloud development. The positive feedback
of land-atmosphere interactions through the PBL development on patchy snow cover and redistribution process of shallow and dry snow cover is discussed in the presentation. This study was
supported by JICA and CEOP-AEGIS projects.
Page | 102
MO-29_B3.2
Föhn events in the lee of the Antarctic Peninsula: a comparison of
observations and model simulations
1
1
1
2
3
Amelie Kirchgaessner , John King , Tom Lachlan-Cope , Phil Anderson , Victoria Smith , Andrew
4
1
3
4
3
1
Elvidge , Russell Ladkin , Alan Gadian , Ian Renfrew , Stephen Mobbs , Gareth Marshall , Andrew
1
Orr
1
2
British Antarctic Survey, Cambridge, United Kingdom, Scottish Association for Marine Science,
3
4
Oban, United Kingdom, University of Leeds, Leeds, United Kingdom, University of East Anglia,
Norwich, United Kingdom
It has been shown that circumpolar westerly winds around Antarctica have increased in strength and
frequency over the past decades. This is thought to increase in turn the occurrence of Föhn events on
the lee (eastern) side of the Antarctic Peninsula, leading to the extreme warming that has been
observed in this area over the last 30 years. This warming will have contributed to the collapse of parts
of the Larsen Ice Shelf in 1995 and 2002.
To investigate how these winds interact with the orographic barrier formed by the Antarctic Peninsula
mountains, and how this interaction influences the regional climate, a comprehensive field campaign
took place in the austral summer 2010/2011.
Observations from an Automatic Weather Station installed on Cole Peninsula (-66°51'S, 63°48'W,
424m asl) will be introduced, and it will be discussed how Föhn events are captured by the data, and
what criteria may be used to automatically identify Föhn events in the observations. One year of AWS
data will be compared with simulations with the Weather Research and Forecasting Model WRF, that
are available through the Antarctic Mesoscale Prediction System AMPS. For this comparison, an
artificial time series has been created from the model output and an independent algorithm was
applied to identify Föhn events. The Föhn detection algorithms and their scoring rate will be presented.
We will also present how the model simulations compare with the observations in general, and how
the model performance changes in the case of Föhn events.
Page | 103
MO-30_B3.2
A Lagrangian climatology of orographic blocking
1
1
1
Michael Sprenger , Erica Madonna , Alexandre Roch
1
Institute for Atmospheric and Climate Science, ETH, Zurich, Switzerland
Orographic blocking refers to the deflection of air streams by mountains. Depending on the impinging
flow, e.g. its wind speed and stratification, and on the mountain geometry the flow either surmounts
the barrier or is deflected - with significant effect on the precipitation and other meteorological fields.
Traditionally, orographic blocking is studied with Eulerian methods based on the estimation of the
inverse Froude number or dimensionless mountain height F=N/HU, where N is the stratification, H the
mountain height and U the usptream velocity. Here we present a Lagrangian perspective of orographic
blocking.
Meteorological fields are taken from the high-resolution NWP model COSMO, which is operationally
run at the Swiss weather service. Winds are taken from a three-year (2000-2002) reanalysis
simulation with 7 km horizontal resolution. Based on these winds, kinematic forward trajectories are
started at a distance of 300 km all around the Alps and at two height levels (750 and 1500 m). The 24h trajectories are then investigated in their capability to surmount the Alpine barrier.
The blocking climatology is separated into three weather classes: westerly flow, northerly flow and
southerly flow, the latter being restricted to south Foehn cases. For each class the percentage of
trajectories surmounting the Alps and the percentage of air parcels flowing around the Alps is
determined. Furthermore, trajectory densities are calculated to show the different air streams which
start from selected upstream positions. The blocking frequencies are compared for air streams starting
at 750 m and at 1500 m.
Finally, the Lagrangian method to identify orographic blocking is compared to the Euerlian one. The
advantages of the Lagrangian method are discussed, as well as its limitations.
Page | 104
MO-31_B3.2
The effects of the Plateau´s topographic gradient on Rossby waves and its
numerical simulation
1
1
Guoping Li , Yu He
1
College of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu, China
By using barotropic model equations that include terrain´s dynamic and thermal effects, this article
theoretically analyzed the characteristics of Rossby waves, the propagation features of wave energy
and the influence of dynamic and thermal effects of the Tibetan Plateau on Rossby waves, also
focused to discuss the effects of the plateau´s topographic gradient on atmospheric Rossby waves.
And then by using the new generation of mesoscale numerical prediction model of WRF3.2 and the
NCEP/NCAR four times daily FNL analysis data, we designed contrast tests of changing the plateau´s
topographic gradient, numerically simulated a process of persistent heavy rain that happened in May
2010 in South China, with model simulations to verify the theory analysis conclusions. The results
based on comparison experiments show that: (1) The exists of large-scale topography of the Tibetan
Plateau is conducive to the formation of atmospheric Rossby waves. (2) While the plateau´s terrain, it
generated friction and heating effects can all make the fluctuations developed into the low-frequency
waves. (3) By making the low- frequency waves generate upstream effect, the dynamic and thermal
effects of the Tibetan Plateau can then affect China´s weather in the form of energy dispersion. (4)
The plateau´s north and south slopes have opposite effects on Rossby wave´s phase velocity, and the
quasi-steady normal fluctuations can be generated when the slopes reached a certain value. (5) Due
to the plateau´s topographic gradient, descending motion appears at the west side (upstream) of the
plateau while ascending motion appears at the east side(downstream), which is conductive to the
occurrence and development of convective activities in the east side of the plateau. (6) The
modulation effect of the plateau´s topographic gradient on Rossby waves enables the fluctuation´s
amplitude enhanced, the wavenumber decreased, and the wavelength of fluctuations get longer.
Page | 105
MO-32_B3.2
Lagrangian perspective on Föhn flow - online and offline trajectories
1
1
1
1
Annette Miltenberger , Stephan Pfahl , Michael Sprenger , Heini Wernli
1
ETH Zürich, Institute for Atmospheric and Climate Science, Zürich, Switzerland
The origin of Föhn air in Alpine valleys and particularly the physical mechanisms behind the warming
of the Föhn air is a long-standing point of discussion - culminating in questioning the thermodynamic
Föhn theory. A very useful tool to tackle this question is the computation of air mass trajectories.
However, the computation of trajectories over complex orography is a quite challenging task, as smallscale structures of the wind field are an essential feature of orographic flows. This requires a high
spatial and temporal resolution of the wind fields used for the computation of trajectories. In this study
we present results from a novel online trajectory module implemented in the regional weather
prediction model COSMO. As the online trajectories are calculated during the integration of COSMO,
the temporal resolution of the wind data and the trajectory integration is strongly increased compared
to classical offline trajectories, which typically rely on hourly mean winds from model output. Results
are shown from simulations of a north Föhn event in July 1987 with different horizontal resolutions of
14 km, 7 km and 2.2 km. The evolution of parcel position, potential temperature and moisture content
is analyzed for air parcels crossing the Alps. We find some significant changes in the representation of
the Föhn flow in the southern Alpine valleys compared to the results from classical offline trajectories.
In general we can conclude that the investigation of Föhn flows can profit from the new online
trajectory tool, and that the online trajectories have an adequate temporal resolution to match the high
spatial resolution of state-of-the-art regional numerical weather prediction models.
Page | 106
MO-33_B3.2
Simulating the mid-winter suppression with a non-spectral Quasi-Geostrophic
model
1
1
Clemens Spensberger , Thomas Spengler
1
Bjerknes Centre for Climate Research, University of Bergen, Bergen, Norway
Mountain ranges contribute significantly to the observed asymmetry of the atmospheric general
circulation between the two hemispheres. The linear effect of orography on the mean atmospheric
state is relatively well understood whereas our understanding of the non-linear impact is still
incomplete. Recent studies showed that the Pacific jet stream maximum in the lee of the Asian
continent cannot be explained as a linear orographic Rossby wave. The Tibetan Plateau appears to
be associated with the midwinter suppression of the Pacific storm track.
We employ the Quasi-Geostrophic (QG) / Semi-Geostrophic (SG) Bergen Dynamic Model (Bedymo)
developed at the University of Bergen to investigate the role of (a) the Himalayas and (b) the Tibetan
plateau on the Pacific storm track. Unlike most QG/SG models the authors are aware of, Bedymo
solves the governing equations in grid-point space, which opens the possibility to introduce new
boundaries within the model domain. Using this mechanism, we assess the role of orographic blocking
of horizontal heat and momentum fluxes in idealised model setups. In these setups, the Himalayas are
modelled as a zonally oriented razor-thin high wall which effectively blocks all meridional transports.
The Tibetan plateau is introduced as a large obstacle with a considerable zonal and meridional extent,
causing flow deflection around the obstacle.
We compare the results including or excluding the Himalayas / Tibetan Plateau in both the QG and SG
frameworks and for different inflow-boundary conditions that mimic the early-winter, mid-winter and
late-winter conditions. Using that set of different model experiments we isolate the processes that lead
to the jet maximum and the mid-winter suppression in the Pacific storm track.
Page | 107
MO-34_B3.2
TKE budget analysis of a single long-lived winter bora flow
1
1
1
Zeljko Vecenaj , Nevio Babic , Branko Grisogono
1
University of Zagreb, Faculty of Science, Department of Geophysics, Zagreb, Croatia
Over the eastern Adriatic coast often blows a downslope windstorm called bora, causing difficulties in
traffic, industry and generally in everyday life. Hence, bora is a subject of intensive scientific research.
While the statistical and synoptic characteristics of the bora flow have been investigated intensively,
some aspects of bora dynamics still remain unexplored, especially its turbulence. This was due to the
lack of suitable measurements needed to asses these aspects, which was especially true for the
middle and southern NE Adriatic coast where, until only recently, no turbulence measurements were
conducted.
A three level tower (10, 20 and 40 m) was equipped with WindMaster Pro ultrasonic anemometers
(Gill Instruments), measuring 3D wind speed and sonic temperature at 5 Hz sampling rate at the top of
Pometeno brdo (≈ 600 m ASL) in Dugopolje (bora upwind site from the city of Split). Measurements
lasted from April 2010 to June 2011, capturing multiple bora events in all annual seasons. This work
concentrates on a single long lasting (more than 120 h) winter bora event on Pometeno brdo. Three
levels of high frequency measurements have made possible the investigation and calculation of the
turbulent kinetic energy (TKE) budget equation. We calculate all terms from the simplified TKE budget
equation (1D model of the TKE budget; horizontal homogeneity assumption is made), except for the
pressure covariance term. We discuss then to what extent the 1D TKE budget model is applicable to
this particular bora event.
Page | 108
MO-35_C2.2
Wind-protected observations of winter precipitation particles for radar QPE in
Niigata region
1
2
1
1
2
Sento Nakai , Manato Fujita , Hiroki Motoyoshi , Masaaki Ishizaka , Toshiro Kumakura , Gyuwon
3
4
5
6
1
7
Lee , Hiroyuki Konishi , Naohiko Hirasawa , Meiji Honda , Satoru Yamaguchi , Takafumi Katsushima ,
8
9
10
Kotaro Yokoyama , Shigeki Murakami , Yoshihide Tominaga
1
Snow and Ice Research Center, National Research Institute for Earth Science and Disaster
2
Prevention, Nagaoka, Japan, Department of Civil and Environmental Engineering, Nagaoka
3
University of Technology, Nagaoka, Japan, Kyungpook National University, Daegu, Korea, Republic
4
5
of, Osaka Kyoiku University, Kashiwara, Japan, National Institute of Polar Research, Tachikawa,
6
7
Japan, Niigata University, Niigata, Japan, Department of Maritime Technology, Toyama National
8
College of Technology, Imizu, Japan, Hokuriku Research Center, National Agriculture and Food
9
Research Organization, Joetsu, Japan, Tohkamachi Experimental Station, Forestry and Forest
10
Products Research Institute, Tokamachi, Japan, Niigata Institute of Technology, Kashiwazaki, Japan
The shape of solid and melting precipitation particles varies significantly. It causes difficulty in
quantitative precipitation estimation (QPE) by radar. Recently, it comes to be possible to measure
diameter and the falling velocity of precipitation particles continuously. We measured these
parameters using several facilities in wind-protected environment, and developed analysis techniques
using the data for improvement of radar QPE.
A CCD-camera system was constructed in a double wind-protection net of the Falling Snow
Observatory (FSO) of SIRC. We also constructed four snow-particle observation stations (SPOSs)
using optical disdrometers. Comparisons between a CCD camera system and optical disdrometers
were also made. High-resolution precipitation gauges were operated aside from optical disdrometer.
SPOSs were installed in the coverage area of an X-band polarimetric radar X-POL. We have
conducted observations for three winter seasons using these facilities.
Number distribution of precipitation particle in size-velocity space is converted to downward water flux
distribution. Then, the weighted-mean diameter and falling velocity are calculated. A parameter riming
and melting index (RMI) is defined to conveniently describe the characteristics of a precipitation
particle. RMI showed a negatively correlated tendency to the coefficient of Ze-R relationship of X-POL
for snow aggregates, although the data was scattered. The coefficient tended to be smaller when the
precipitation intensity was stronger for snow aggregates and graupel. Differences in precipitation
particle characteristics were found among the data of the four sites. Statistical analysis of these data
and comparison with radar Ze and with polarimetric parameters such as Zdr will contribute to the
development of GPM standard algorithms. The results will contribute to snow-related disaster
prediction and the radar-based winter QPE.
Page | 109
MO-36_C2.2
Numerical simulations of melting snowflakes by using Moving Particle Semiimplicit (MPS) method
1
Hiroshi Ishimoto
1
Meteorological Research Institute, Tsukuba, Japan
Because of the resent progress of numerical techniques and computer performances, microwave
scattering properties of ice crystals and snowflakes in their realistic shapes can be calculated by using
some semi-analytical methods, such as DDA and/or FDTD method. For melting ice particles, however,
their scattering properties have not been studied well, because of our insufficient understanding for the
detailed morphology and mixing state of liquid water in the melting phase of non-spherical and
complex shaped ice particles. In this work, a numerical code to simulate the melting of ice particles
has been developed. We assume that the ice particle is formed by constituent particles, and the
Moving Particle Semi-implicit (MPS) method is used to simulate the dynamics of melted liquid water.
The MPS method is one of the particle methods that solve Navier-Stokes equation in Lagrangian
approach. The method derives implicit solution for pressure gradient term at each time step, and the
constituent particles are forced to satisfy the continuity equation. For the algorithm of ice melting,
enthalpy information is applied for the composed particles and heat transfer between the particles is
calculated. Heat from outer atmosphere and latent heat by vaporization are also considered to be
consistent with the equation proposed by Mitra et al. (1990). Preliminary results of melting simulations
for some snowflake models are proposed. Scattering properties of the melting ice particles derived by
using FDTD method are briefly discussed.
Page | 110
MO-37_C2.3
Ground based in situ measurements of arctic cloud microphysical and optical
properties at Mount Zeppelin (Ny-Alesund Svalbard): preliminary results
1
1
1
1
2
Gwennole Guyot , Valery Shcherbakov , Olivier Jourdan , Alfons Schwarzenboeck , Peter Tunved ,
1
1
1
1
Frans Oloffson , Régis Dupuy , Guy Febvre , Chistophe Gourbeyre
1
2
Laboatory of Physics Meteorology, Clermont-Ferrand, France, Department of Applied Environmental
Science (ITM), Stockholm University, Stockholm, Sweden
The high sensitivity of the polar region to the global climate warming, due to singular feedbacks
existing in this region, was shown by many studies. In particular, climate simulations suggest that
cloud effects play an important role in arctic warming [Hassol, 2005]. Moreover, high seasonal
variability in aerosol properties was measured in the Arctic by [Engwall et al., 2008; Tunveld et al.,
2012]. In consequence, changes in cloud properties are expected during the wintersummer transition
but not well understood yet. Consistent efforts are thus made nowadays to improve our knowledge of
the temporal variation of the cloud geometrical, optical and microphysical properties, especially for low
level stratiform clouds.
In this context, a set of ground-based cloud measurements was performed in Mt Zeppelin, in NyAlesund, Svalbard, by the LaMP (Laboratory of Physics Meteorology, Clermont-Ferrand, France)
th
nd
between March 6 and May 2 2012. This instrumentation was composed of a CPI (Cloud Particle
Imager), which takes pictures of particles in the size range of [15µm-2.3mm]; a FSSP (Forward
Scattering Spectrometer Probe) for the microphysics of cloud droplets [3-45µm]; a Polar
Nephelometer, which gives the phase function [3-800µm], and a Nevzorov Probe, which provides
liquid and ice water content. This instrumentation, combined with additional data from CPC
(Condensation Particle Counter) and DMPS (Differential Mobility Particle Spectrometer), allowed us to
study the aerosol properties, the cloud properties and thus the aerosol cloud interaction during the six
cases in presence of mix phase low level clouds. In addition, we were able to carry out measurements
of the optical and microphysical properties of blowing snow (2 cases) and snow precipitation (5 cases).
Blowing snow is characterized as irregular small particles, around 250 µm, and precipitation as big
particles, around 1 mm, with stellar shape dominance. Some relationships between morphological and
optical properties will be reported.
Page | 111
MO-38_C2.3
In-situ measurements of the microphysical properties of mixed-phase clouds
with a digital holographic instrument
1
2
1
1
Jan Henneberger , Jacob P. Fugal , Olaf Stetzer , Ulrike Lohmann
1
2
Institiute for Atmospheric and Climate Science, ETH Zurich, Zürich, Switzerland, Institute for
Atmospheric Physics, Johannes Gutenberg-University, Mainz, Germany
Mixed-phase clouds are common in the atmosphere and the radiative budget and the hydrological
cycle are particularly sensitive to the partition of the cloud phase. Nevertheless there is a lack of
observations of the micro structure of mixed-phase clouds with a high temporal and spatial resolution.
We developed a new version of the HOLographic Imager for Microscopic Objects (HOLIMO II), which
images single cloud particle using digital in-line holography. Holography offers size and shape
information of cloud particles sampled simultaneously in a well defined sample volume. Because
holography provides real images of particles, no assumption concerning their shape has to be made.
HOLIMO II is a stand-alone and remote controlled field instrument to measure in-situ the size, the
concentration and the spectrum of cloud particles larger than 6.8µm. The accuracy and precision of
the particle sizing algorithm was measured using mono dispersed beads. These results were used to
correct for deviations of the sizing, particularly for small particle sizes near the detection limit.
Results from field campaigns during winter time at the Swiss High Alpine Research Station
Jungfraujoch at an elevation of 3571 m will be presented. To validate the new instrument, the
measured particle size distributions were compared to other in-situ cloud instrument for different
mixed-phase cloud cases. Observing the temporal development of microphysical properties of mixedphase clouds over several hours allows us to analyze the variation of the number concentrations of
cloud droplets and ice crystals.
Page | 112
MO-39_C2.3
Comparison of Cloudsat/CALIPSO cloud observations with ground-based
measurements over the Greenland and Antarctic ice sheets
1
2
1
3
4
Kristof Van Tricht , Stef Lhermitte , Irina V. Gorodetskaya , Jan Schween , David D. Turner , Nicole
1
P.M. Van Lipzig
1
2
Department of Earth and Environmental Sciences, KU Leuven, Leuven, Belgium, Royal Netherlands
3
Meteorological Institute (KNMI), Utrecht, Netherlands, Institute of Geophysics and Meteorology,
4
University of Cologne, Cologne, Germany, NOAA National Severe Storms Laboratory, Norman,
United States
Clouds play a key role in the climate of the polar regions. Understanding cloud properties and their
climate feedback therefore is paramount to ensure the realism of future climate projections. Despite
the importance of the cloud effects, climate models struggle to accurately represent clouds, particularly
over the ice sheets. The recent availability, however, of cloud radar (Cloudsat) and lidar (CALIPSO)
satellite observations have enlarged the observational dataset of clouds in the polar regions. Together
with an extensive ground-based remote sensing instrument set at the Summit station in Greenland
and the Princess Elisabeth station in Antarctica, these data provide new opportunities for studying
clouds and their radiative forcing. This study aims at validating Cloudsat and CALIPSO cloud
measurements for the Summit and Princess Elisabeth stations, based on various cases including
clear-sky conditions, typical low-level stratus clouds, clouds with liquid, ice or mixed phase and
precipitating as well as non-precipitating clouds. Validation consists of comparing the satellite
observations with ceilometer, micropulse lidar, millimeter cloud radar and radiosonde measurements
(Greenland) and ceilometer and micro rain radar measurements (Antarctica). Results show an overall
good agreement between satellite and ground-based observations, with sensitivity of both groundbased and satellite-based lidars to optically thin ice clouds, while radar images provide information
about optically thick clouds which the lidars cannot penetrate. Optically thin ice clouds are more
difficult to detect than liquid-containing clouds. A newly developed ceilometer algorithm, specifically
adapted to polar regions, detects the base height of the lowest hydrometeor layers, which provides a
quantitative basis for validating satellite observations. A successful validation will lead to the
construction of a cloud climatology over the ice sheets, ultimately enabling us to investigate cloudclimate feedback mechanisms.
Page | 113
MO-40_C2.3
Optical thickness and effective radius of Arctic boundary-layer clouds retrieved
from airborne spectral and hyperspectral radiance measurements
1
1
1
Manfred Wendisch , Eike Bierwirth , Andre Ehrlich
1
Institute for Meteorology, University of Leipzig, Leipzig, Germany
Arctic boundary-layer clouds in the vicinity of Svalbard (78 N, 15 E) were observed with airborne
remote sensing and in situ methods. The cloud optical thickness and the droplet effective radius are
retrieved from spectral radiance data in nadir and from hyperspectral radiances in a 40 degrees field of
view around nadir. Two approaches are used for the spectral retrieval, combining the signal from
either two or five wavelengths. Two wavelengths are found to be sufficient for an accurate retrieval of
the cloud optical thickness, while the retrieval of droplet effective radius 10 is more sensitive to the
method applied. The comparison to in situ data cannot give a definite answer as to which method is
better because of unavoidable time delays between the in situ measurements and the remote-sensing
observations, and due to the scarcity 15 of in situ profiles within the cloud.
Page | 114
MO-41_C2.3
Analysis and numerical simulation of a regional warm fog
1
2
3
1
Zhaoxia Hu , Hengchi Lei , Xing Yu , Xiaoqing Zhang
1
2
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China, Institue of
3
Atmospheric Physics, Chinese Academy of Sciences, Beijing, China, Institute of Meteorological
Science of Shaan'xi, Xi'an, China
The main purpose of this work is to analysis a regional fog episode occurred in mostly area of mid and
east China from 17 to 19 December 2004 based on the observation and MM5 modeling. The
characteristics of regional fog and evolution process are investigated. The results show that it is a
typical radiation fog event with a large spatial scale and the horizontal distribution is not uniform. The
fog appears at the surface firstly and then expended to the high level. The burst developing features of
fog are not found. The temperature inversion and abundant water vapor are the beneficial factors to
the fog formation and maintaining as well as light wind. The influences of shortwave radiation warming
and longwave radiation cooling are examined.
Page | 115
MO-42_C2.3
Analysis of first large-scale precipitation process in spring in Tianjin
1
1
1
Ruijun Jin , Wei Song , Zhaoyu Wang
1
Tianjin Weather Modification Office, Tianjin, China
Based on Doppler Weather Radar data, weather maps and satellite cloudy products, a large-scale
rainfall on 18 April 2009 in Tianjin is analyzed. The characteristics of Doppler Weather Radar products
and the distribution of cloud parameters during this rainfall process are discussed. The results show
that: (1) it was a stratocumulus mix cloud precipitation process, affected by the Hetao low trough at
500 hPa and surface cyclones over the Yangtze-Huaihe River Valley; (2) the reflectivity of Doppler
Radar presented the obvious multi-phased characteristic: forming, developing, maintaining, and
weakening with the complete wind profiler data; (3) during the MODIS satellite passing time, the
effective radius of cloud particles was above 15 µｍ, and the particle radius with the highest
appearance frequency was 25 to 27 µｍ. The area with the maximum atmospheric potential
precipitation was consistent with the hourly precipitation of the automatic rainfall station.
Page | 116
MO-43_C2.3
Investigation of clouds, precipitation and aerosol processes at high latitudes
1
1
Kaori Sato , Hajime Okamoto
1
Kyushu University, Kasuga, Japan
Statistics and vertical variability of the microphysical properties of clouds and precipitation, derived
from CloudSat/CALIPSO data globally, are discussed with emphasize on their high latitude
characteristics. Processes involved in the interrelation among the identified cloud microphysics, cloud
phase, precipitation quantity and associated aerosol types are studied by combination of several
retrieval algorithms (involving mostly active sensors), developed as part of the standard algorithms for
the upcoming Japanese/European joint earth observation mission EarthCARE (Earth Clouds, Aerosol
and Radiation Explorer). The analyzed results are also presented in concern with their quantitative
representation in climate models along the satellite orbits.
Page | 117
MO-44_C2.3
Ice nucleation ability of kaolinite in the contact freezing mode
1
1
1
Baban Nagare , Olaf Stetzer , Ulrike Lohmann
1
Institute for Atmosphere and Climate Science, ETH, Zurich, Switzerland
The importance of heterogeneous ice nucleation via contact freezing is a topic of discussion of the
atmospheric science community. In our lab, we built the Collision Nucleation CHamber (CLINCH)
(Ladino et al. 2011) in which falling cloud droplets can collide with aerosol particles. In this study,
contact freezing experiments at ice saturation are conducted to investigate the ice nucleation ability of
kaolinite. Kaolinite is a mineral found in desert dust. It is known to be a relatively good ice nucleus. In
our experiments, size selected kaolinite particles of 200, 400 and 800 nm mobility diameter and water
droplets of 40 and 80 µm diameter interact in CLINCH. With the new extension of the chamber length
was increased to 80 cm and makes it is possible to vary the interaction time of ice nuclei and the
droplets. Our experiments are performed between -10 to -36ºC and for various ice nuclei
concentrations. The frozen fraction of the droplets is determined using the in-house built depolarization
detector IODE (Nicolet et al., 2010). Depolarization of linearly polarized incident laser light is used to
determine the ratio of frozen droplets to all droplets. Frozen fractions of droplets with different
residence times inside CLINCH will be compared to previous results and will be presented in this
study.
Page | 118
MO-45_C2.3
Urban and aerosol effects on the stratiform cloud and the light precipitation
1
1
2
Seung Hee Eun , Byung Gon Kim , Seung Soo Lee
1
2
Gangneung-Wonju National University, Gangneung, Korea, Republic of, NOAA/ESRL/Chemical
Sciences Division, and CIRES, Colorado, United States
Many observational and numerical studies have indicated that urbanization and aerosol effect modify
cloud property, precipitation, and further weather pattern over and downwind of urban region. But it is
still unclear quantitatively how urban and aerosol have an influence on the precipitation (Tao et al.,
2012). Our previous research (Eun et al. 2011) showed an increasing trend of precipitation amount
and frequency from 1972 to 2007, especially less than 1 mm per day (light precipitation) and westerly
condition only. It implies the possible urban and aerosol effect on the precipitation at downwind region
of urban area. Based on observed results, we selected golden case (11 February 2009) to investigate
the impact urbanization and aerosol on light precipitation using the Weather Research and
Forecasting (WRFv3.4) model.
The result of sensitivity experiment with increase in anthropogenic heat (10 times than control
experiment; AH) indicates that precipitation amount increases over and downwind region of Seoul
Metropolitan Area (SMA), mostly attributable to the enhanced convergence and its associated updraft.
On the other hand, increasing number concentration of Cloud Condensation Nuclei (CCN) in the whole
model domain leads to a decrease in precipitation amount in the downwind area of SMA with an
increase in cloud number concentrations and a decrease in cloud drop size. The additional experiment
with both AH and CCN shows the similar behavior to those of CCN simulation. Also the result of AH
and CCN allocated in the SMA region only will be discussed in detail in the meeting.
Page | 119
MO-46_C2.3
Relationship of heavy snowfall events to low-level stability and air-sea
temperature difference in the Yeongdong Region, Korea
1
2
3
Hyounggu Nam , Byung Gon Kim , Sang Ok Han
1
2
Gangneung-Wonju National University, Gangneung, Korea, Republic of, Department of Atmospheric
Environmental Sciences, Gangneung-Wonju National University, Gangneung, Korea, Republic of,
3
High Impact Weather Research Center, National Institute of Meteorological Research, Gangneung,
Korea, Republic of
Characteristics of heavy snowfall episodes have been investigated during the past ten years, in order
to understand the association with low-level stability and air-sea temperature difference in the
Yeongdong region, which has big (Taeback) mountain with adjacent East Sea. In general, the
selected heavy snowfall episodes have similar synoptic setting such as the Siberian High extended to
East Sea along with the Low passing by the southern Korean Peninsula, eventually inducing easterly
wind in the Yeongdong region.
For the heavy snowfall episodes, specifically moist-adiabatically unstable layer has been identified
over the East sea due to relatively warm sea surface temperature (SST) about 8~10 ℃ and lower
temperature around 1~2 km above the surface, being derived from data assimilation. Sea-air (850hPa)
temperature difference and snowfall intensity in case of the heavy snowfall events are almost larger
than 20 ℃ and 8 times greater than the weak snowfall, respectively. In summary instability-induced
moisture supply to the atmosphere from the East Sea, being cooled and saturated by the upper cold
surge, would make low-level ice cloud, which eventually move inland by the easterly flow and result in
heavy snowfall.
Page | 120
MO-47_C2.3
Aerosol radiative characteristics according to data of expedition
measurements in the regions of Spitsbergen, Tiksi, and Antarctica
1
1
1
Tatiana Zhuravleva , Sergey M. Sakerin , Dmitrii M. Kabanov
1
V.E. Zuev Institute of Atmospheric Optics SB RAS, Tomsk, Russian Federation
The report discusses our studies of the atmospheric aerosol optical depth (AOD) in three polar
regions: in Spitsbergen (Barentsburg, Aprils - Augusts of 2011-2012), on the coast of the Laptev Sea
(Tiksi, June 2010), and in the South Ocean near Antarctica (2006-2011). In the measurements of AOD
and moisture content W of the atmosphere in Arctic regions, we used the SPM sun photometer (0.342.14 µm). The observations in Tiksi were performed in the period when ocean and coast were still
snow covered. The average AOD under these conditions was 0.088 in the region of 0.5 µm and the
Angstrom exponent exhibited very large value α =1.8. Observations in Spitsbergen during 2011
showed that AOD decreased from spring toward summer: from 0.101 to 0.065 in the region of 0.5 µm.
The measurements in 2012 revealed no seasonal AOD variations: the average value was 0.095 (0.5
µm).
The measurements of the atmospheric spectral transparency in the South Ocean were performed
using Microtops II and SPM photometers during 51st-57th Russian Antarctic expeditions. The results
of the vessel observations and comparison with measurements at Mirny station showed that the
average AOD values in Antarctica varied in a narrow range of values: 0.02-0.04 (0.5 mm).
We performed a comparative analysis of finely and coarsely dispersed components of AOD and
spectral AOD dependences in the polar regions. The results of the expedition measurements of AOD
and W served as a basis for estimating the aerosol radiative forcing. The data on the aerosol
scattering phase function and single scattering albedo in high-latitude regions were scarce; therefore,
model values of these characteristics were used in the radiation calculations.
This work was supported by the Program of Basic Research of the Presidium of RAS (No. 23) and by
the RFBR (No. 13-05-00806).
Page | 121
MO-48_C2.3
Apparent aerosol transmission from 1909 to 2010 at Davos, Switzerland
1
1
Daniel Lachat , Christoph Wehrli
1
PMOD/WRC, Davos-Dorf, Switzerland
Solar radiation and atmospheric transmission have been of increasing interest in climate research in
the past decades. In this context, recent studies have observed decadal trends in solar radiation
received at the Earth's surface. They claim a decrease of solar radiation starting from the 1950s to the
end of the 1980s followed by an increase from the 1990s to present. These periods are refered to as
Global Dimming and Global Brightening (1), respectively. Trends in cloud coverage and atmospheric
transmission are prime focal points in the quest for possible causes of this variability.
Pyrheliometric measurements have been carried out at the PMOD/WRC from 1909 until present which
results in the longest stationary direct irradiance record. A variety of radiometers and changing
measurement scales had to be adjusted to the World Radiometric Reference (WRR).
Following the Ratioing Technique used by Hoyt and Fröhlich (2), apparent atmospheric transmission
was obtained by calculating the ratio of irradiances, interpolated at two fixed airmasses from a fit
through observations. In the 1970s, apparent atmospheric transmission over Davos shows a slight
transition from Dimming to Brightening which is more pronounced if favourable seasonal subsets are
analysed.
Recently, there are efforts to analyse the Dimming and Brightening trends by separating the
contributions of water vapour absorption and aerosol extinction (3). This implies the factorization of
transmission into Rayleigh scattering and water vapour absorption, and interpreting the residual as
aerosol extinction. Therefore, Integrated atmospheric Water Vapour (IWV) has been estimated from
specific humidity and 2m-temperature measurements. Estimated IWV and GPS measurements are in
good agreement.
Atmospheric transmission accounting for water vapour absorption and Rayleigh scattering respectively
have been simulated using a simple radiative transfer model. The resulting IWV-transmission-series
and the residual series of apparent aerosol transmission are analysed for decadal trends.
Page | 122
MO-49_C2.3
Ground-based aerosol optical depth in polar stations of the GAW-PFR network
1
1
1
2
1
Natalia Kouremeti , Julian Gröbner , Stephan Nyeki , Elina Giannakaki , Christoph Wehrli , Kerstin
3
4
5
3
Stebel , Karl Schroff , Veijo Aaltonen , Jan H. Wasseng
1
2
PMOD/WRC, Davos Dorf, Switzerland, Finnish Meteorological Institute, Kuopio Unit, Kuopio,
3
4
Finland, Norwegian Institute for Air Research (NILU), Kjeller, Norway, Institute for Atmospheric and
5
Climate Science, ETH, Zürich, Switzerland, Finnish Meteorological Institute, Research and
Development, Helsinki, Finland
Arctic regions have been shown to be strongly influenced by changes in the Climate System.
Specifically, the magnitude of aerosol radiative forcing in Polar Regions is largely uncertain due to
spatial inhomogeneities, the variable surface albedo and the solar geometry. Furthermore, due to the
high latitude, measurements are only available for part of the year. In general, the quantification of the
direct and indirect forcing by aerosols remains an outstanding problem.
Measurements of atmospheric aerosols in the Arctic environment began in the 1950s, when first
observations of haze were reported. Since then many studies have verified this fact. On the other
hand, as Antarctica is more isolated from human activities; lower aerosol concentrations compared to
Arctic regions are expected. The Global Atmosphere Watch (GAW) program in collaboration with the
Norwegian Institute for Air Research (NILU) and Finnish Meteorological Institute (FMI) run two Arctic
and two Antarctic stations in order to study the polar aerosol environment.
In this work we present an overview of aerosol optical properties measured at four polar stations, Ny
Alesund (78.9N, 11.9E), Summit (72.6N, 38.4W), Troll (72.0S, 2.5E) and Marambio (64.2S, 56.6W),
which are part of the GAW-PFR AOD network. The measurements are performed with Precision Filter
Radiometers (PFR) which provides spectral aerosol optical depth at 368, 412, 500 and 862 nm.
Seasonal aerosol optical properties at these sites are presented and discussed. Moreover we
investigate cases of possible long-range transport of aerosols using the Hybrid Single Particle
Lagrangian Integrated Trajectory model (HYSPLIT) in order to gather information about their origin.
Page | 123
MO-50_C2.3
Aerosol and cloud properties during meteorological regimes with and without
precipitation at Utsteinen, Dronning Maud Land, East Antarctica
1
2
3
4
4
Alexander Mangold , Irina Gorodetskaya , Christian Hermans , Stefan Kneifel , Maximilian Maahn ,
1
2
Hugo De Backer , Nicole Van Lipzig
1
2
Royal Meteorological Institute of Belgium, Brussels, Belgium, Catholic University of Leuven, Leuven,
3
4
Belgium, Belgian Institute for Space Aeronomy, Brussels, Belgium, University of Cologne, Cologne,
Germany
Aerosols play an important role in the atmospheric hydrological cycle. They act as cloud condensation
and ice nuclei and play a crucial role in the formation of clouds, affecting both cloud macro- and
microphysics. Clouds are important agents in the Antarctic hydrological cycle, linking water vapour
transport into Antarctica with precipitation.
We will present aerosol, cloud and precipitation properties from simultaneous measurements at the
Belgian Antarctic research station Princess Elisabeth (PE), situated north of the Sør Rondane
Mountains in Dronning Maud Land, East Antarctica, around 180 km inland from the coast.
Physical and optical aerosol data from a multi-wavelength aethalometer and nephelometer, an
ultrafine condensation particle counter, and an aerosol sizing spectrometer are combined to
characterise the boundary layer aerosol. A sunphotometer provides aerosol information for the total
atmospheric column. Aerosol properties like mean size, width of size distribution, presence of particle
formation events, spectral dependencies of scattering, absorption and single scattering albedo enable
to classify the aerosol as fresh, locally formed or aged, long-range transported aerosol and to
determine the presence and importance of dust, sea salt and rather scattering or light-absorbing
aerosol.
Together with aerosol properties, we analyse ceilometer backscatter profiles showing the nature of
clouds (optically thin icy or optically thick liquid-containing, virga or precipitation to the surface),
infrared pyrometer cloud base temperature, and precipitation occurrence from a 24 GHz vertically
pointing precipitation radar.
The analysis focuses on the austral summer season 2012/13. Using data from an automatic weather
station and multivariate hierarchical cluster technique, time periods of the two predominant
meteorological regimes at PE are selected -cold katabatic (air originated in the Antarctic interior) and
synoptic (associated with the advection brought by extratropical cyclones and frontal systems). We
compare the aerosol-cloud characteristics during some synoptic events with precipitation to periods
with a katabatic meteorological regime.
Page | 124
MO-51_C2.3
In situ aerosol measurements at Dome C, on the high plateau of East
Antarctica
1
2
2
2
2
Aki Virkkula , Emma Järvinen , Tuomo Nieminen , Riikka Väänänen , Hanna E. Manninen , Pasi P.
2
1
2
3
3
3
Aalto , Eija Asmi , John Backman , Maurizio Busetto , Chistian Lanconelli , Angelo Lupi , Mauro
3
3
2
1
2
2
Mazzola , Vito Vitale , Tuukka Petäjä , Risto Hillamo , Veli-Matti Kerminen , Markku Kulmala
1
2
Finnish Meteorological Institute, Helsinki, Finland, Department of Physics, University of Helsinki,
3
Helsinki, Finland, Institute of Atmospheric Sciences and Climate of the Italian National Research
Council, Bologna, Italy
In situ aerosol measurements have been conducted at the Dome C station (75˚S, 123˚E) on the upper
plateau at about 3200 m amsl since December 2007. Part of these measurements have been
continuous since then, part of them only for shorter periods. Particle size distributions have been
measured ranging from the subnanometer to supermicron sizes and light absorption at three
wavelengths.
The size distributions in the size range 10 - 600 nm have been measured with a differential mobility
particle sizer (DMPS) and with a Grimm Model 1.108 optical particle counter in the size range 0.3 - 15
µm. They were first stopped at the end of year 2009 due to technical problems but they were
continued again in December 2010, and the goal is to continue these measurements. In December
2010 also a new instrument, an Air Ion Spectrometer (AIS), that measures charged particle size
distributions in the size range of about 0.8 - 40 nm, was installed at the station. The AIS produced
good data until May 2011.
There was a clear seasonal cycle in the number concentration data. The concentrations were at their
lowest around July and August and at highest around January, which is in agreement with the data
from all other stations in Antarctica. New particle formation events did occur all year round, even in the
darkest and coldest months June and July. These events were weak but not nonexistent, which is a
new and interesting phenomenon, not reported earlier from the upper plateau of Antarctica. The AIS
measurements show that often these particles do not grow to sizes larger than approximately 10 nm.
Page | 125
MO-52_C2.3
Observing the diurnal cycle of bioaerosols in remote and urban environments
using 5-D single-particle UV-LIF and agglomerative hierarchical cluster
analysis
1
2
3
4
4
Martin Gallagher , Ian Crawford , Neil Robinson , Joshua L. Malkinson , Christopher Daniel , Warren
5
5
R. Stanley , Paul H. Kaye
1
2
University of Manchester Centre for Atmospheric Science, Manchester, United Kingdom, Centre for
3
Atmospheric Science, University of Manchester, Manchester, United Kingdom, UK Meteorological
4
Office, Exeter, United Kingdom, Physics, University of Manchester, Manchester, United Kingdom,
5
Centre for Atmospheric Instrumentation Research, University of Hertfordshire, Hertford, United
Kingdom
Agglomerative hierarchical cluster analysis was applied to continuous single particle 5-dimensional
UV-LIF measurements from a wideband integrated bioaerosol spectrometer to investigate the diurnal
cycle of airborne bacterial and fungal spores in remote tropical environments and compared to urban
environments, including indoor large multiple use public buildings. Cluster solutions highlight different
diurnal patterns for the different bioaerosols appearing at different times of the day. Natural emissions
are contrasted with urban emissions the latter, including indoor air being linked to and enhanced by
both internal human presence and activities. The impact of external activities including biomass
burning are also able to be segregated from internal activities using this approach.
Page | 126
MO-54_C6.1
Analysis of snow cover in the Himalayan region using remotely sensed data
1,2
Sunal Ojha
1
2
Ministry of Energy, Nepal Electricity Authority, Kathmandu, Nepal, Graduate School of Environmental
Studies, Nagoya University, Nagoya, Japan
Satellite remote sensing is an effective tool for monitoring snow covered area. However, complex
terrain and heterogeneous land cover and the presence of clouds, impose challenges to snow cover
mapping. This research analyzes snow cover and glaciers with a perspective of climate change in
Himalayan Regions using remote sensing techniques. The remote sensing snow cover data from
Moderate Resolution Imaging Spectroradiometer (MODIS) satellite from 2000 to 2010 have been used
to analyze some climate change indicators. In particular, the variability in the maximum snow extent
with elevations, its temporal variability (8-day, monthly, seasonal and annual), its variation trend and
its relation with temperature have been analyzed. The snow products used in this study are the
maximum snow extent and fractional snow covers, which come in 8-day temporal and 500m and 0.05
degree spatial resolutions respectively. The results showed a tremendous potential of the MODIS
snow product for studying the spatial and temporal variability of snow as well as the study of climate
change impact in large and inaccessible regions like the Himalayas. The snow area extent (SAE) (%)
time series exhibits similar patterns during seven hydrological years, even though there are some
deviations in the accumulation and melt periods. The analysis showed relatively well inverse relation
between the daily mean temperature and SAE during the melting period. Some important trends of
snow fall are also observed. In particular, the decreasing trend in January and increasing trend in late
winter and early spring may be interpreted as a signal of a possible seasonal shift. However, it
requires more years of data to verify this conclusion. Significant coverage of lake ice was found in
lower elevation zone which is due to flat terrain in this zone.
Key Words: Climate change, Himalayas, MODIS, remote sensing, snow, lake ice.
Page | 127
MO-53_C2.3
Underestimation of the greenhouse effect by supercooled water clouds
1
1
1
Penny Rowe , Steven Neshyba , Von P. Walden
1
University of Idaho, Moscow, Idaho, United States
Simulations of cloud radiative properties for climate modeling and remote sensing in the polar regions
rely on accurate knowledge of the complex refractive index (CRI) of water. Although conventional
algorithms employ a temperature independent assumption (TIA), recent infrared measurements of
supercooled water have demonstrated that the CRI becomes increasingly ice-like at lower
temperatures. Here, we assess biases that result from ignoring this temperature dependence. We
show that TIA-based cloud retrievals introduce spurious ice into pure, supercooled clouds, or
underestimate cloud thickness and droplet size. TIA-based top-of-atmosphere fluxes are higher by as
2
much as 2 W/m (for an Arctic summer / Antarctic coastal summer model), while downwelling radiative
2
fluxes are lower than those for the temperature-dependent CRI by as much as 1.7 W/m (for an Arctic
winter / Antarctic interior summer model). Proper accounting of the temperature dependence of the
CRI, therefore, leads to significantly greater local greenhouse warming due to supercooled clouds than
previously predicted. The current experimental uncertainty in the CRI at low temperatures must be
reduced to properly account for supercooled clouds in both climate models and cloud property
retrievals.
Page | 128
MO-55_C6.1
Persistence in intra-annual snow depth distribution. Part II: fractal analysis of
snow depth development
1,2
2
Michael W. Schirmer , Michael Lehning
1
2
Applied Snow and Avalanche Research (ASARC), University of Calgary, Calgary, Canada, WSL
Institute for Snow and Avalanche Research SLF, Davos, Switzerland
We present an analysis of high resolution laser scanning data of snow depths in the Wannengrat
catchment (introduced in Part I) using omni-directional and directional variograms for three specific
terrain features; cross-loaded slopes, lee slopes and windward slopes. A break in scaling behavior
was observed in all sub-areas, which can be seen as the roughness scale of bare earth terrain which
is modified by the snow cover. In the wind-protected lee slope a different scaling behavior was
observed, compared to the two wind-exposed areas. The wind-exposed areas have a smaller ordinal
intercept γ, a smaller short range fractal dimension D and a larger scale break distance L than the
wind-protected lee slope. Snow depth structure inherits characteristics of dominant NW storms, which
results e.g. in a trend towards larger break distances in the course of the accumulation season. This
can be interpreted as a result of surface smoothing at increasing scales. Similar scaling characteristics
were obtained for two different years at the end of the accumulation season. Since snow depth
structure is altered strongly by NW storms, this inter-annual consistency may strongly depend on their
frequency in an accumulation period. With the analysis of directional variograms anisotropies of fractal
parameters were detected, which were related to dominant wind directions.
Page | 129
MO-56_C6.1
Flexible visualisations for SNOWPACK and Alpine3D
1
2
1
1
1
Nicholas Dawes , Ionut Iosifescu , Mathias Bavay , Christine Groot-Zwaaftink , Nander Wever
1
2
WSL – Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland, Institute for
Cartography and Geodesy, ETH Zürich, Zürich, Switzerland
The SLF snow cover and micrometeorology group is responsible for the development of two physical
environmental models: SNOWPACK and Alpine3D. SNOWPACK is a 1-dimensional physically-based
model of the snow cover and its interaction with the atmosphere. The difficulty of SNOWPACK
visualisations is that the output files are organised into layers; each of these layers has a time
dependent height, so the output values cannot be specified by height, only by layer number.
Throughout the lifetime of SNOWPACK, the operational visualisation of results has depended on a
custom Java interface (now reaching the end of its life), or extremely specialised visualisations created
by the users, who often start from scratch each time. Alpine3D is a spatially distributed (surface), 3dimensional (atmospheric) model of snow-dominated surface processes in mountainous topography.
Visualisation of spatially distributed Alpine3D results has mostly depended on a basic, custom Java
interface or GIS software e.g. ArcGIS. Importing ASCII grids to GIS software usually requires many
steps to import each output file and visualize a single time-step.
In this contribution, we will describe a number of tools for the visualisation of SNOWPACK and
Alpine3D output files, which we have programmed in scientific programming languages (Matlab, R,
LabVIEW) and made publicly available. We will also describe our use of the Swiss Experiment
Platform (SwissEx) as a data repository and the use of the web-services in the visualisation of data
through the same tools. Using the SwissEx WebGIS, we will demonstrate early prototypes of our webbased visualisation of 3- and 4-dimensional (3 spatial dimensions plus time) Alpine3D output with
simplified navigation and data handling. In the future, such tools will be used with a grid/cloud-based
scratch database system, allowing the user to easily visualize simulations made in the grid/cloud
without first copying it to a permanent data storage solution.
Page | 130
MO-57_C6.1
Intra-seasonal variability of snow spatial patterns over one winter season on
Haut Glacier d'Arolla, Switzerland
1
2
2
2
2
Saskia Gindraux , Francesca Pellicciotti , Marco Carenzo , Ilaria Clemenzi , Alvaro Ayala , Paolo
2
Burlando
1
2
Department of Geography, University of Zurich, Zurich, Switzerland, Institute of Environmental
Engineering, ETH, Zurich, Switzerland
The winter phase of snow accumulation has been little investigated as compared to melt processes in
mass balance models, and simple assumptions for snow redistribution are still common. A number of
recent studies have looked at the characteristics of snow spatial distribution using statistically analysis.
These investigations have been conducted in several areas with distinct elevation, aspect, topography
and altitude but only few studies have been conducted in high mountains and even fewer on glaciers.
A tool commonly used to identify patterns and characteristics of the snow distribution is fractal analysis
of scaling properties of snow. This has been used to characterise the distribution of snow at the peak
season, as well as establish whether winter season accumulation exhibited distinct patterns over two
different years. Only one previous study has investigated the intra-annual consistency of snow depth
within one accumulation season. Our study aims at understanding if snow accumulation during one
winter season is persistent and what its main controls are, using fractal properties and scale
invariance.
We use data collected during repeated winter surveys over one season on Haut Glacier d'Arolla,
which provided snow depth measurements in two quadrants in the upper basin and lower tongue
respectively. Data are analyzed by calculating the semi-variogam, fractal dimension and scale break.
Meteorological data were also collected at four different locations on the glacier to understand the
factors responsible for the changes in snow cover, such as precipitation patterns, meteorological
conditions and wind redistribution. Our results are also compared to those obtained from LiDAR snow
depth fields at the peak of accumulation, which showed persistence from one year to the other.
Page | 131
MO-58_C6.1
Spatial snow variability on slopes of the Khibini Mountains
1
2
3
4
Pavel Chernous , Yuri Fedorenko , Nikolay Barashev , Evgeny Mokrov
1
2
Center for Avalanche Safety, 'Apatit' JSC, Kirovsk, Russian Federation, Polar Geophysical Institute,
3
4
Apatity, Russian Federation, Avalanche Service, NWPC JSC, Apatity, Russian Federation, Faculty of
Geography, Moscow State University, Moscow, Russian Federation
A study of snow characteristics spatial variability by means of statistics is presented.
Methods and results of snow thickness, density, shear strength; hardness and temperature special
measurements for the Khibini Mountains' slopes are submitted. Obtained spatial autocorrelation
functions are very similar for the most of the characteristics. The similarity can be explained by
common spatial structure of the snow forming factors. As comparison shows, variances of the snow
characteristics (except temperature) in the Khibini Mountains are much more than ones in other areas.
It is explained by influence of the strong wind during snowfalls. Methods of statistical simulation to
obtain the snow characteristic spatial distributions and possibilities to use them for stochastic
snowpack stability assessment are described.
Page | 132
A4.2a - Sea ice and Ocean-Atmosphere Interactions
09.07.2013 08:15-09:45, Sanada II
691
Reducing uncertainty in 21st century projections of Arctic sea ice loss and
associated impacts
1
2
1
Julienne Stroeve , Andrew Barrett , Mark Serreze
1
2
National Snow and Ice Data Center, University of Colorado, Boulder, United States, University of
Colorado, Boulder, United States
A major source of uncertainty bearing on evolution of the Arctic sea ice cover through the remainder of
the 21st century is the sea ice thickness distribution. While it follows that models with an overly thick
initial (early 21st century) ice cover will tend to lose their summer ice at a slower rate than models with
initially thinner ice given the same climate forcing, the ice thickness distribution strongly determines
surface heat fluxes, impacting both the ice mass budget and ice loss rate, which in turn strongly
controls Arctic amplification - the outsized rise in lower-tropospheric air temperatures over the Arctic
Ocean compared to lower latitudes. This study is focused on narrowing the envelope of uncertainty in
projections of sea ice extent under different emissions scenarios, using output from the latest
generation of coupled global climate models (the CMIP5 archive) through a model selection process.
The selection process emphasizes: (1) how well each model simulates the present-day (late 20th and
early 21st century) mean sea ice thickness distribution and extent and statistics of interannual
variability, using sea ice thickness data from submarines, IceBridge, ICESat-1, ERS1/2, ENVISAT and
CryoSat-2 and the time-series from satellite passive microwave data for extent; and (2) how well each
model reproduces the observed atmospheric temperature and key features of the Arctic atmospheric
circulation that bear on ice extent and thickness distributions (both Arctic-wide and regional), based on
evaluations against fields from next-generation atmospheric reanalyses (NCEP CFSR and ERAInterim).
Page | 133
693
Impact of the implementation of new processes on the simulation of the Arctic
sea ice cover by CNRM-CM5
1
1,2
1
1
Salas y Melia David , Matthieu Chevallier , Agathe Germe , Stéphane Sénési
1
2
METEO-FRANCE / CNRM-GAME, Toulouse, France, MERCATOR-OCEAN, Ramonville, France
Gelato5 is a multi-category and multi-layer sea-ice model coupled with NEMO3.2 and ARPEGE-Climat
within CNRM-CM5 (about 1° horizontal resolution), one of the CMIP5 global coupled climate models.
In comparison with CNRM-CM3 (CMIP3), the sea ice model contains new features. Sea ice salinity is
now interactive, and the ice specific heat (Cp), enthalpy and vertical heat diffusion coefficient (Ki) are
functions of ice temperature and salinity.
The aim of this study is to assess the impact of these new features on the simulation of the mean state
and recent melting of sea ice during the 1990-2009 time-span. To do so, a 10-member set of 18502012 coupled simulations including Gelato5 was carried out with CNRM-CM5. This set of simulations
serves as a control and allows to assess the internal variability of the sea ice cover over 1990-2009.
This set shows that CNRM-CM5 correctly reproduces the recent sea ice depletion trend observed in
the Arctic, but the simulated sea ice thickness is underestimated for all ensemble members. To
understand this bias, a forced experiment was run with the ocean-sea ice component of CNRM-CM5
(NEMO-Gelato), using an ERA-Interim-based forcing data set during 1990-2009. This experiment
shows that the sea ice thickness bias in coupled mode originates from an overestimation of the
surface incoming solar radiation.
Sensitivity experiments are run in coupled and forced mode respectively with CNRM-CM5 and
NEMO1-Gelato, fixing sea ice salinity, Cp or Ki. Comparing these experiments with the control set of
experiments shows that fixing Cp or Ki leads to even thinner ice, and tends to accelerate the shrinking
of the sea ice cover. By contrast, fixing the salinity of ice does not change the mean state or trend
significantly.
Page | 134
623
The role of sea ice on the Atlantic overturning circulation in a coupled global
ocean-ice model
1
Yongming Tang
1
European Centre for Medium-Range Weather Forecasts (ECMWF), Reading, United Kingdom
Sea ice is an integral part of the whole global climate system, and hence climate models for seasonal
and decadal predictability need to incorporate reliable sea ice components. In particular, the
initialisation of sea ice through the assimilation of available data is crucial for obtaining reliable and
robust forecasts. We have run three numerical experiments with contrasting sea ice initialisation and
data assimilation using the NEMO ocean model coupled with the LIM2 sea ice model, forced using
bulk formulae and the ECMWF ERA-interim data, and run for the period 1987-2011. The three
simulations result in significant differences for both Arctic sea ice extent and sea ice volume. In this
talk we report on the impact of these different initialisation schemes on the Atlantic meridional
overturning circulation.
Page | 135
138
Arctic sea ice evolution in CMIP5 extended RCP scenarios
1
1
1
Paul Hezel , Thierry Fichefet , François Massonnet
1
TECLIM, Université catholique de Louvain, Louvain-la-Neuve, Belgium
The global climate models that particiapated in the Coupled Model Intercomparison Project 5 (CMIP5)
show strong declines in sea ice extent and volume under the some of the Radiative Concentration
Pathway (RCP) scenarios through the year 2100, including the transformation from perennial to
seasonal ice cover in multiple models in RCP4.5 and RCP8.5. These simulations were extended
through the year 2300 by a subset of the CMIP5 modeling groups for the three scenarios RCP2.6,
RCP4.5, and RCP8.5. These radiative forcing trajectories are decreasing, constant, and increasing
respectively through 2300. Here, we examine the time evolution of Arctic sea ice in these extended
RCP scenarios to gauge the response to these forcing pathways. In the RCP2.6 scenario, the summer
Arctic sea ice extent begins to slowly recover almost immediately following the peak radiative forcing
in 2044 in 6 of the 9 models that ran the extended RCP2.6 simulations. The extended RCP4.5
scenario maintains constant radiative forcing at 4.5 W/m^2 through 2300 and demonstrates continued
summer sea ice decline due to continued warming on longer time scales.
The different sea ice respsonse in these two scenarios implies that sea ice extent could recover if and
when radiative forcing from greenhouse gases were to decrease. In the RCP8.5 scenario, we show
that the winter sea ice extent disappears in 7 of 9 models between 2135 and 2233, at a radiative
forcing between 10 and 12 W/m^2. We discuss the reasons that cause the lack of ice formation in the
models during the winter under this particular scenario.
Page | 136
75
A study of impact of enthalpy sea ice modeling and data assimilation on
decadal predictability with a pycnocline prediction model
1
2
3
4
Shaoqing Zhang , Xinrong Wu , Mike Winton , Zhengyu Liu
1
2
GFDL/NOAA, New Jersey, United States, National Marine Data and Informaion Service of China,
3
4
Tianjing, China, GFDL/NOAA, Princeton, United States, Peking University of China, Beijing, China
A1-D enthalpy sea ice model has been implemented into a simple pycnocline prediction model to
examine the impact of enthalpy sea ice modeling and data assimilation on decadal predictability. The
1-D enthalpy sea ice model includes the physical processes such as brine expulsion, flushing and salt
diffusion. After being coupled with the “atmosphere” and “ocean” components, the enthalpy sea ice
model can be integrated stably and serves as an important modulator of model decadal variability. The
observation-assimilation simulation experiment shows that, due to the continuous probability
distribution of the enthalpy, the sea ice data assimilation in the enthalpy space can produce physicallyconsistent coupled states through coherent incorporation of sea ice observations into the coupled
model. The results in this study suggest that, once the corresponding physically-consistent sea ice
data assimilation with an enthalpy sea ice model is implemented into a coupled general circulation
model, the quality of climate estimation and prediction can be progressively improved. This study also
serves as the first step of the efforts towards developing an enthalpy sea ice model component in a
coupled climate model.
Page | 137
C6.1/C6.4 - Properties and variability of the mountain snow cover / Avalanche
protection, measures and hazard mapping
09.07.2013 08:15-09:45, Aspen II
845
Simulating melt crust and ice lens formation in a physically based snowpack
model
1
1
1,2
Nander Wever , Charles Fierz , Michael Lehning
1
2
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland, CRYOS, School of
Architecture, Civil and Environmental Engineering, École Polytechnique Fédéral de Lausanne,
Lausanne, Switzerland
Water flow in a natural snow cover is generally a complex process because of the strongly stratified
and changing structure of the snowpack. Important differences in, for example, density and grain size
between layers cause sometimes very sharp transitions in hydraulic properties. Experiments have
shown that water accumulating on capillary barriers in the snow cover can reduce its strength and
thereby favour wet snow avalanche formation. Refreezing at capillary barriers within the snow cover
leads to the formation of ice lenses or ice crusts, which favors the development of large-grained weak
layers (facets and depth hoar). During the melt season, crusts and large grains strongly influence the
vertical water flow in snow. Blocking of the vertical flow can lead to lateral flow or to delayed arrival of
melt water at the bottom of the snowpack.
We extended the model SNOWPACK with a solver for 1D unsaturated flow (Richards Equation), which
considerably improved melt water runoff estimations. Here we show that Richards Equation is also
capable of reproducing capillary barriers at interfaces between snow layers of differing properties; a
real modelling challenge. Moreover, the method to determine the hydraulic conductivity at the interface
nodes between snow layers plays a major role in the behaviour of simulated water flow. Comparing
the arithmetic with the so-called Darcian averaging approach for internodal hydraulic conductivity, we
show that the latter is able to reproduce important accumulation of liquid water at interfaces within the
snowpack. Refreezing of this water leads to layers that can be considered crusts or ice lenses, with
higher densities than layers above and below. We compare the simulation results with observed snow
profiles. The ability of SNOWPACK to reproduce melt-freeze crusts and ice lenses will be helpful in
future studies on travel times of water through the snowpack or assessing snowpack stability.
Page | 138
429
Avalanche risk zoning as a total loss minimisation problem
1
2
1
1
Nicolas Eckert , Eric Parent , Mohamed Naaim , Philomene Favier
1
2
IRSTEA, Saint Martin d'Heres, France, AgroParisTech/INRA, UMR 518 Math. Info. Appli, Paris,
France
Using high return period avalanches as reference events has the advantage of using the same
thresholds than for other hazards (e.g. 100 years), but severe drawbacks. First, the reference event
considered remains undefined from the perspective of the runout pressure joint distribution. Second, it
does not explicitly take into account the elements at risk, possibly leading to inacceptable risk levels.
Hence, the individual risk concept has been recently introduced in the engineering practice and an
optimal design framework based on decision theory has been proposed for avalanche
countermeasures. The aim of this work is to bridge these attempts, showing how avalanche risk
zoning can result from the minimization of total losses, leading the best compromise between
expected fatalities and urbanization constraints with regards to the stake holder's behavior against
risk. It requires the determination of the statistical values of human life and of urbanized areas. The
first one can be elicited for each case study from the stake holder's choices. The second one can be
roughly approximated from the total economic value of a mountain community.
First, the simplifying assumption of a constant death probability conditional to the avalanche hit is
made. With a simplified peak over threshold model, this leads analytical solutions, i.e. high and
moderate risk limits as explicit optimal functions of model parameters under both classical and
Bayesian paradigms. Second, it is shown that additional decisional variables such as a dam height
can be easily accounted for, illustrating that the proposed framework is able to handle the main
challenges of avalanche long term forecasting in a consistent manner. Finally, death probabilities
functions of the position are tested, as a first step before a full numerical implementation. This all may
have a great impact of hazard mitigation theory and practices.
Page | 139
1179
LiDAR mapping of snow depth in avalanche starting zones in Iceland for
assessing avalanche hazard and design of supporting structures
1
Tómas Jóhannesson
1
Icelandic Meteorological Office, Reykjavík, Iceland
Snow avalanches threaten several coastal villages in northwestern, northern and eastern Iceland. An
effort for assessing avalanche risk and construct avalanche protection measures was initiated after
two catastrophic avalanches killed 34 persons in the villages Flateyri and Súðavík in 1995. Snow
depth in avalanche starting zones in Iceland is greatly affected by redistribution of snow by wind in the
maritime climate of the country. Accurate information about the spatial distribution of snow depth is
therefore essential for hazard zoning and for optimal design of avalanche supporting structures. Aerial
lidar surveying of snow-covered mountainsides in May 2008 and of the same areas free of snow in the
fall of 2008 and 2009 have been used to construct snow depth maps for eight mountainsides above
avalanche-threatened villages in Iceland. Validation measurements by manual probing of snow depth
were carried out on the same day in one of the areas, confirming excellent accuracy of the derived
snow depth to within ~10 cm. The snow depth maps clearly show the preferential accumulation of
snow in depressions and on the lee side in gullies. The maps also shows interesting formations of
thick snow drifts at other locations that can be 5-10 m thick and >100 m long and seem to be caused
by wind flowing up steep gullies or around bedrock protuberances. The snow depth maps have proved
useful for detailed determination of structure heights in the design of supporting structures in the
Hafnarfjall mountainside above the village of Siglufjörður in Northern Iceland.
Page | 140
197
Exploring the snow lateral variability within a 20 m snow trench at Concordia
Station, East Antarctica
1
1
1
1
Fabiano Monti , Christine D. Groot Zwaaftink , Martin Schneebeli , Charles Fierz , Giovanni
2
3
Macelloni , Anselmo Cagnati
1
2
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland, Institute of Applied
3
Physics “Nello Carrara”, Sesto Fiorentino, Italy, ARPAV CVA, Arabba di Livinallongo, Italy
Although the East Antarctic plateau has few significant topographic features, snow stratigraphy on the
first meters is strongly heterogeneous in space. This variability is mainly caused by wind, which affects
snow surface features such as zastrugi and dunes, dominating snow deposition and its properties
(snow density, grain size, and grain shape).
This heterogeneity of the snow cover prevents an easy comparison between snow profiles both in
space and time, hindering interpretation of remote sensing data (e.g. microwave measurements).
Moreover, it challenges our ability to develop a better understanding of snow cover development
based solely on punctual snow profile records. Indeed, changes in snow stratigraphy due to either
temporal evolution or spatial variability are hardly distinguishable.
Snow cover simulations could help gaining insight in the snow cover development. However, as profile
matching layer by layer is difficult, model validation is currently limited to the surface energy balance
and snow temperatures.
In this study, we explore whether we could obtain more insight through a series of adjacent snow
profiles to characterize the spatial variability. Then we might better tackle the temporal effect on the
evolution of the snow cover. During the 2012-2013 summer campaign, a snow trench 20 m long and
1.80 m deep was dug near Concordia Station at Dome C. In addition to three full snow profiles, we
recorded snow stratigraphy with infrared pictures. Our observations confirm the limited lateral
continuity of snow layers and the strong influence of the wind. Layers within the 3 profiles could not be
matched, but in each profile, similar stratigraphic patterns can be identified.
We investigate the effect of snow metamorphism and wind on the formation of these patterns and
explore whether snow cover models can assist in understanding those, especially for winter periods
when manual observations are missing.
Page | 141
1143
Improvements in the design of snow avalanche impact resisting buildings from
back-analyses on real events
1
1
Valerio De Biagi , Bernardino Chiaia , Barbara Frigo
1
Politecnico di Torino, Torino, Italy
1
Damages on real scale structures give an effective possibility to engineers and researchers to
understand the response of constructions to the actions impressed by natural phenomena. The
damages caused by the extreme snow avalanche of Les Thoules in Aosta Valley on December 2008
are analysed and the main features of the response of the totally and partially collapsed structures to
snow flow are highlighted. Collapse mechanisms are emphasized and their limit capacity is computed.
The results of the back-analysis are then turned into prescriptions and indications for the design of
buildings under snow avalanche hazard. Pressure distribution on corners as well as structural detailing
play a fundamental role in the overall robustness of the construction. An example on a new house is
presented.
Page | 142
A6.3a - Ice melt in Antarctica and Greenland and its implication for ice sheet
and ice shelf stability in the 21st century
09.07.2013 08:15-09:45, Forum
1193
Response of grounded ice to the disintegration of northern Larsen Ice Shelf,
Antarctic peninsula
1,2
1
1
1
3
4
Helmut Rott , Jan Wuite , Markus Hetzenecker , Thomas Nagler , Dana Floricioiu , Michael Kern
1
2
ENVEO IT, Innsbruck, Austria, Meteorology and Geophysics, University of Innsbruck, Innsbruck,
3
4
Austria, IMF, DLR, Oberpfaffenhofen, Germany, ESA-ESTEC, Noordiwjk, Netherlands
The Larsen Ice Shelf on the Antarctic Peninsula has been subject to accelerating retreat due to
climate warming which culminated in the collapse of the two northernmost ice shelf sections, the
Larsen-A and Prince Gustav Channel ice shelves in January 1995, followed by disintegration of the
northern and central sections of Larsen-B in March 2002. During the years preceding the
disintegration events, satellite images show extended periods of summer melt, formation of rifts and
crevasses, and acceleration of ice shelf flow. After these events the glaciers previously feeding the ice
shelves became tidewater glaciers. The perturbations triggered strong acceleration of glacier flow. We
analysed time series of satellite-borne imaging radar (SAR) data, starting in the 1990s with the ESA
missions ERS-1 and ERS-2, followed by Envisat and the German TerraSAR-X and TanDEM-X
missions. Retreating ice fronts, the formation of fractures and rifts, and the ice flow on Larsen A and B
ice shelves and its tributary glaciers were mapped. Changes of surface topography were analysed
using altimeter data of NASA's ICESat and ESA's CryoSat missions, and digital elevation data of
TanDEM-X. The analysis of time series of glacier flow indicates that the acceleration was triggered by
stress perturbation at the glacier front propagating rapidly upstream through dynamic coupling. This
resulted in extensive mass depletion for all major glaciers draining into the embayments of the
previous ice shelves. Recent data show for several glaciers of the Larsen-A and -B embayments
gradual decrease of calving velocities associated with dynamic thinning, indicating gradual dynamic
adjustment of the terminus and beginning decrease of mass loss.
Page | 143
912
Bimodal probability of the dynamic contribution of Antarctica to future sea
level
1
1
2
2
3
Catherine Ritz , Gael Durand , Tamsin Edwards , Anthony J. Payne , Richard C.A. Hindmarsh ,
1
Vincent Peyaud
1
2
UJF-Grenoble/CNRS LGGE, Saint Martin d'Hères, France, School of Geographical Sciences,
3
University of Bristol, Bristol, United Kingdom, Science Programmes, British Antarctic Survey,
Cambridge, United Kingdom
Recent observations of glacier acceleration along Antarctic margins raise the issue of their future
dynamics and consequent contribution to sea level. One crucial driver of the acceleration is suggested
to be enhanced sub-ice shelf melting, which reduces the ability of floating ice shelves to buttress the
upstream flow of grounded ice-streams. Modelling the response to such forcing in glaciers upstream is
currently hampered by the poor ability of current ice sheet models to simulate the evolution of the
grounding line, which delimits the downstream extent of ice that could impact on sea level. Here, using
ensemble simulations of the GRISLI ice sheet model, we estimate the evolving probability distribution
of the future dynamic contribution of Antarctica to sea level until 2200 induced by retreat of the
grounding line under the SRES A1B scenario. Considering linear basal drag, our result at 2200 is
bimodal, with the highest probability mode at 7.8 cm and a lower probability mode at +47.5 cm (sea
level rise). We estimate the total dynamic contribution of Antarctica to sea level will be less than 49.9
cm in 2200 (90% credibility interval). These results are considerably lower than previous estimates
based on extrapolation or kinematic arguments. The Amundsen Sea sector contribution dominates
throughout the next two centuries, while the Ronne-Filchner, Queen Maud, Princess Elizabeth, Wilkes
Land and George V sectors only contribute substantially during the second century. We estimate that
large scale destabilization of the Amundsen Sea sector is unlikely, with a probability of only around
10%.
Page | 144
1135
Potential for past and long-term future retreat of West Antarctica and the East
Antarctic ice sheet margin
1
2
Robert DeConto , David Pollard
1
2
University of Massachusetts, Amherst, United States, Pennsylvania State University, State College,
United States
The middle Pliocene epoch (~3 million years ago) is often considered an analogue for future global
climatic conditions, because global mean temperatures were comparable to projections of future
climate at the end of this century. Importantly, some estimates of mid-Pliocene sea level are >20 m
higher than today, implying the potential for significant retreat of the East Antarctic Ice Sheet (EAIS) in
addition to the loss of the Greenland and West Antarctic Ice Sheets (WAIS). Here, we use a hybrid ice
sheet-shelf model coupled to a high-resolution regional climate model to test the potential for both
West and East Antarctic Ice Sheet retreat during the warm Pliocene and in long-term future scenarios
with elevated CO2. In these simulations we apply new treatments of ice shelf calving and basal sliding,
improved sub-glacial bathymetry using BEDMAP2, and a range of plausible ocean warming scenarios
based on offline ocean modeling. In warm Pliocene simulations, the combination of improved
bathymetric detail and more physically based model treatments substantially increases the sensitivity
of the EAIS margin, implying the EAIS could have contributed to elevated Pliocene sea levels. In long3
term (10 -yr) future simulations, we find the combination of elevated CO2 and modest ocean warming
is capable of driving WAIS retreat and some grounding line retreat into the Wilkes Basin of East
Antarctica. At CO2 levels around 1000 ppmv, we find the potential for substantial retreat into the
Wilkes Basin and along parts of the Wilkes margin. While enhanced precipitation in the EAIS interior
partially compensates for marginal ice sheet retreat, the net sea level contribution is positive, with the
redistribution of ice mass from West to East Antarctica having an important effect on regional sea
level.
Page | 145
1226
Long-term Antarctic surface elevation trends from satellite radar and laser
altimetry
1
2
Rakia Meister , Brian Gunter
1
2
Division of Geodynamics, DTU Space, Kongens Lyngby, Denmark, Department of Geosciences and
Remot Sensing, TU Delft, Delft, Netherlands
The last decade has seen dramatic changes in the Antarctic ice sheet (AIS), which is home to over
60% of the world's fresh water reserve. The acceleration of Antarctica's outlet glaciers has led to a
negative mass balance in Western Antarctica, while accumulation anomalies in the East suggest a
positive mass balance in some areas. In this project we examine the volume change, and subsequent
surface mass balance, of the AIS over the past decade using both satellite radar data from the RA-2
radar on Envisat, which was operational from 2002 to 2012, and laser altimetry observations from the
GLAS instrument aboard the Ice, Cloud and Land Elevation Satellite (ICESat), which gathered
measurements from 2003 to 2009. Both missions collected valuable information about the surface
elevation changes of the AIS, but the spatial and temporal resolution of the individual measurements
were substantially different. The radar altimetry measurements had footprints sizes on the order of
kilometres, while the laser footprints were approximately 70m. The orbit inclination of ICEsat (86°)
allowed it to cover more of the polar regions than Envisat (81.6°); however, the ICESat measurements
were only gathered in 33-day campaigns, two or three times per year, while Envisat was operational
nearly continuously (and over a longer time span). In addition to the variations in spatiotemporal
resolution, the radar pulses from Envisat can penetrate 1m or more into the firn, while the nearinfrared laser shots from ICEsat reflect off the surface. Despite these differences, we find that the
trends derived from the individual missions are highly correlated in both spatial distribution and
magnitude. Investigating the volume of 27 individual basins reveals that while most basins show good
agreement, discrepancies do exist which are likely due to errors associated with issues such as radar
penetration, sampling frequency, atmosopheric effects, and others.
Page | 146
1237
Accumulation, melting, and dynamic-driven mass changes of the Antarctic ice
sheet
1
2
2
H. Jay Zwally , Jun Li , Weili Wang
1
Cryospheric Sciences Laboratory, NASA Goddard Space Flight Center, Greenbelt, United States,
2
Code 615 NASA Goddard SFC, SGT, Inc., Greenbelt, United States
Mass changes of the Antarctic ice sheet derived from satellite altimetry over the last two decades are
shown to be combinations of contemporaneous meteorological-driven changes in snow accumulation,
recent dynamic-driven changes induced by ice-shelf melting, century-scale dynamic thickening or
thinning from stagnation or restarting of ice-streams, and millennia-scale imbalances between ice flow
and long-term accumulation. Results from ICESat laser altimetry show that during 2003-2008 mass
gains from snow accumulation exceed losses from ice discharge by 73 Gt/yr (0.20 mm yr-1 sea level
depletion). Results from ERS radar altimetry for 1992-2001 give a similar net gain of 120 Gt/yr. The
net gain in East Antarctica (EA) and four West Antarctic (WA) drainage systems (WA2) exceed net
losses from three WA coastal drainage systems (WA1) and the Antarctic Peninsula (AP). Some of the
dynamic changes in WA are on century time-scales, including inland dynamic thickening from
stagnation of the Kamb ice stream 150 years ago. In EA and WA2, the most of the net mass gain is
caused by persistent dynamic thickening (deficiency of ice flow relative to long-term accumulation) at a
rate of 207 Gt/yr, and not by contemporaneous increases in snowfall. The dynamic thickening in EA
and WA2 is consistent with a marked precipitation increase at the beginning of the Holcene, as shown
by ice core data and a dynamic model experiment. In WA1 and AP, increased losses of 68 Gt/yr
between the two periods from greater dynamic thinning associated with accelerating outlet glaciers are
40% offset by greater snow accumulation in WA and AP. These decadal-scale changes are small
relative to the long-term dynamic thickening, which may buffer additional increases in dynamic thinning
keeping the overall mass balance positive for several decades.
Page | 147
C2.3b - Clouds, aerosols and precipitation at high latitudes
09.07.2013 08:15-09:45, Studio
101
A structure of an As-Cs cloud system in Arctic
1
2
Andrey Sinkevich , Paul Lawson
1
Cloud Physics and Atmospheric Electricity, Main Geophysical Observatory named by A.I.Voeikov, St.
2
Petersburg, Russian Federation, SPEC Inc., Boulder, United States
Results of aircraft investigations of the microphysical structure and properties of an As-Cs cloud
system in the Arctic are presented. Data were collected over the Beaufort Sea using the US National
Center for Atmospheric Research (NCAR) C-130 aircraft. It was found that the cloud consisted of
several layers of limited horizontal length. Spherical crystals were the prevailing habit. A decrease in
their concentration with height decrease was discovered. Measurements of particle size spectra
indicate their significant inhomogeneity. Spectra parametrization was carried out with the help of a
gamma distribution for particles smaller than 50 µm and with exponential distribution for particles
larger than 50 µm.
Page | 148
419
Investigation of Arctic mixed-phase clouds using the regional model COSMOCLM
1,2
1,2
Sara Pousse-Nottelmann , Ulrike Lohmann
1
2
Institute for Atmospheric and Climate Science, ETH, Zürich, Switzerland, Center for Climate Systems
Modeling (C2SM), Zurich, Switzerland
Average temperatures in the Arctic have risen almost twice as much as compared to the global rate
[IPCC, 2007]. It is believed that the change in the Arctic climate is considerably affected by aerosol
and cloud feedbacks. Observations revealed that the Arctic cloud population is dominated by longlived mixed-phase clouds. Aerosols can impact the persistence of these clouds by influencing the
cloud microphysical processes. They can act as cloud condensation nuclei, influencing number and
size of the present cloud droplets, as well as ice nuclei, impacting the formation of ice.
Adequate simulation of Arctic clouds is therefore essential to address questions regarding Arctic
climate change. The simulation of observed ice crystal number concentrations proved to be most
challenging for modeling studies. However, recent studies [e.g. Avramov et al., 2011] found agreement
between simulated and measured ice crystal number concentration when assuming entrainment from
a below-cloud ice nuclei reservoir.
In the present study, springtime Arctic clouds over Alaska are simulated using the regional weather
forecast and climate model COSMO-CLM. The model version includes a two-moment cloud
microphysical scheme [Seifert & Beheng, 2006] that has been coupled to the aerosol module M7
[Vignati et al., 2004]. The model has been extended by an explicit treatment of cloud-borne aerosol
particles following the approach by Hoose et al. (2008), in order to account for cloud cycling of
aerosols by tracking the particles even when scavenged into hydrometeors.
The model output will be compared to airborne observations from the Indirect and Semi-Direct Aerosol
Campaign (ISDAC), which was conducted near Barrow, Alaska in April 2008 [McFarquhar et al.,
2011]. Questions regarding the ability of the model to simulate the persistence of Arctic mixed-phase
clouds will be addressed. Particular emphasis will be placed on the study of the relation between ice
nuclei and ice crystal number concentration.
Page | 149
596
Electrial signatures of low-level stratiform clouds in ground level atmospheric
electricity data at mid-latitude station Swider, Poland
1
1
1
2
Anna Odzimek , Marek Kubicki , Piotr Baranski , Danuta Jasinkiewicz
1
Department of Atmospheric Physics, Institute of Geophysics, Polish Academy of Sciences, Warsaw,
2
Poland, Stanislaw Kalinowski Geophysical Observatory, Institute of Geophysics, Polish Academy of
Sciences, Otwock-Swider, Poland
Atmospheric electricity parameters have been monitored at the Geophysical Observatory in Swider,
Poland (52.12 N, 21.24 E), for the last few decades. In this work we look at the behaviour of these
parameters in the presence of low-level stratiform clouds at a mid-latitude location such as Swider.
Firstly, we analyse the frequency of such cloud types occurrences, depending on season and
accompanying meteorological phenomena, over recent years. Next we investigate variations of the
atmospheric electric field and vertical current density at ground level, and look for the evidence of
electric current generation by the clouds. Better understanding of the role of the clouds in the
atmospheric electrical system is necessary for the studies of the global atmospheric electrical circuit
and the circuit's coupling with other atmospheric systems. This work has been supported by Polish
National Science Center grant 2011/01/B/ST10/07188.
Page | 150
709
Arctic ice clouds observed by LiDAR at AFARS: how they differ from their
midlatitude counterparts
1
1
Kenneth Sassen , Vinay K. Kayetha
1
Geophysical Institute, University of Alaska, Fairbanks, United States
Knowledge of the Earth's clouds has until recently been dominated by midlatitude research, but it is
clear from the global CALIPSO satellite dataset that the distribution and physical properties of various
cloud types is a strong function of latitude and geography. Here, we examine the differences between
high (i.e., cirrus) and midlevel (altostratus) ice clouds based on multi-year polarization lidar
measurement programs from FARS in Salt lake City, Utah (40.82°N, 111.88°W), and AFARS (the
Arctic Facility for Atmospheric Remote Sensing) in Fairbanks, Alaska (64.86°N, 146.84°W). Although
the average monthly cloud base and top temperatures of cirrus (defined as cloud top temperatures < 40°C and optical depths < ~3.0 based on FARS research) are similar, the heights, pressures, and
wind speeds/directions are very different, as are their lidar linear depolarization ratios. The
discrepancies in macrophysical cloud properties are of course a reflection of the differences in
tropopause heights (normally about 2-km lower at AFARS), and the weather patterns locally
responsible for cirrus generation. However, the differences in lidar depolarization (an indication of ice
crystal shape) are more intriguing, and agree with the trend in the global CALIPSO data. Major
differences are also indicated in the frequency and properties of midlevel ice clouds, which at high
latitudes often are optically thin or even subvisual particularly during the winter season, and appear to
occur in smaller mesoscale cloud organizations. We provide and compare ice cloud climatologies from
FARS and AFARS and discuss the implications for the improved global characterization of ice clouds,
and raise the question whether our midlatitude definition of cirrus is appropriate for cirrus clouds in the
Arctic.
Page | 151
903
Ice and liquid partitioning in mid-latitude and arctic mixed-phase clouds: how
common is the truly mixed-phase state
1
2
2
3
3
4
Jessica Meyer , Martina Kraemer , Armin Afchine , James Dorsey , Martin Gallagher , Phil Brown ,
5
6
5
5
Manfred Wendisch , Alan Woolley , Andre Ehrlich , Eike Bierwirth
1
2
IEK-7, Forschungszentrum Juelich, Juelich, Germany, Forschungszentrum Juelich, Juelich,
3
4
Germany, University of Manchester, Manchester, United Kingdom, Met Office, Exeter, United
5
6
Kingdom, Universität Leipzig, Leipzig, Germany, FAAM, Cranfield, United Kingdom
The influence of mixed-phase clouds on the radiation budget of the earth is largely unknown. One of
the key parameters to determine mixed-phase cloud radiative properties however is the fraction of ice
particles and liquid droplets in these clouds. The separate detection of liquid droplets and ice crystals
especially in the small cloud particle size range below 50 µm remains challenging though.
Here, we present airborne NIXE-CAPS mixed-phase cloud particle measurements observed in
midlatitude and Arctic low-level mixed-phase clouds during the COALESC field campaign in 2011 and
the Arctic field campaign VERDI in 2012. NIXE-CAPS (Novel Ice EXpEriment - Cloud and Aerosol
Particle Spectrometer, manufactured by DMT) is a cloud particle spectrometer which measures the
cloud particle number, size as well as their phase for each cloud particle in the diameter range 0.6 to
945 µm.
The common understanding in mixed-phase cloud research is that liquid droplets and ice crystals in
the same cloud volume are rather sparse, but instead either liquid droplets or ice crystals are present.
However, recently published model studies (e.g. Korolev, A. & Field, P., The effect of dynamics on
mixed-phase clouds: Theoretical considerations. J. Atmos. Sci. 65, 66-86, 2008) indicate that a cloud
state containing both liquid droplets and ice crystals can be kept up by turbulence. Indeed, our particle
by particle analyses of the observed mixed-phase clouds during COALESC and VERDI indicate that
the real mixed-phase state is rather common in the atmosphere. The spatial distribution of the mixedphase ice fraction and the size of the droplets and ice crystals however vary substantially from case to
case. The latter parameters seem to be influenced not only by concentration of ice nuclei but also - to
a large degree - by cloud dynamics.
Page | 152
1004
Arctic mixed phase clouds properties based on airborne in situ and remote
sensing measurements
1
1
1
1
1
Guillaume Mioche , Olivier Jourdan , Frédéric Szczap , Gwennolé Guyot , Christophe Gourbeyre ,
1
2
1
Régis Dupuy , Julien Delanoe , Alfons Schwarzenboeck
1
2
Laboratoire de Météorologie Physique, Aubière, France, Laboratoire Atmosphères, Milieux,
Observations Spatiales, Guyancourt, France
Clouds radiation feedback processes in Polar Regions have been identified as key uncertainties in the
prediction of global climate in GCMs. To better understand clouds-radiation interactions in these
regions, knowledge of arctic clouds properties has to be improved. In particular, mixed phased clouds,
which frequently occur in Arctic, present a large variety of physical characteristics and involve very
complex microphysical and dynamical processes between liquid and ice phases, currently not yet well
understood, and poorly documented.
In order to improve the knowledge of arctic clouds properties, the Laboratoire de Météorologie
Physique (LaMP) is involved from several years in several airborne measurement campaigns
dedicated to the study of arctic clouds (ASTAR 2004, ASTAR 2007, POLARCAT 2008, SORPIC
2010), providing optical and microphysical in situ measurements from a unique combination of
airborne probes (CPI, Polar néphélomètre, PMS FFS-100, 2D-S, Nevzorov…). Furthermore, the
airborne radar/lidar system RALI from LATMOS will provide in addition active remote sensing
measurements.
This study will present a statistical analysis of arctic mixed phase clouds optical and microphysical
properties based on these in situ measurements, representing more than 40 flights.
The first main objective of this study is to investigate the ice particles and clouds droplets growth
processes into the clouds, and their interaction with radiation. The second main objective is to provide
accurate profiles of relevant clouds parameters to contribute to the improvement of clouds
representation in global and mesoscale models and to improve airborne and spatial remote sensing
retrievals algorithms (CALIPSO, CloudSat, EarthCare…). These relevant parameters are for example
the thermodynamic phase, geometrical characteristics (height, thickness), and optical and
microphysical properties (asymmetry parameters, optical depth, liquid/water fraction, ice crystals
morphology, size and concentration, IWC…).
Page | 153
B3.1/B3.2 - General dynamics / Dynamics of mountain weather and climate
09.07.2013 08:15-09:45, Wisshorn
65
Mechanisms of banner cloud formation
1
1
Volkmar Wirth , Matthias Voigt
1
University of Mainz, Mainz, Germany
Banner cloud are clouds in the lee of steep mountains or sharp ridges. Their formation has previously
been hypothesized as due to three different mechanisms:
(i) vertical uplift in a lee vortex, (ii) adiabatic expansion along quasi-horizontal trajectories (the socalled Bernoulli-effect), (iii) a mixing cloud, i.e. condensation through mixing of two unsaturated air
masses.
In the present work, these hypotheses are tested and quantitatively evaluated against each other by
means of Large Eddy Simulation. The model setup is chosen such as to represent idealized, but
prototypical conditions for banner cloud formation. It is found that the lee vortex mechanism is very
likely to be the most relevant explanation for banner cloud formation. Key aspect is a pronounced
windward-leeward asymmetry in the Lagrangian vertical uplift with a plume of large positive values in
the immediate lee of the mountain; this allows the region in the lee to tap moister air from closer to the
bottom surface. By comparison, the horizontal pressure perturbation is more than two orders of
magnitude smaller than the pressure drop along a trajectory in the rising branch of the lee vortex; the
``Bernoulli mechanism´´ is, therefore, very unlikely to be a primary mechanism. Banner clouds are
unlikely to be ``mixing clouds´´ in the strict sense of their definition. However, turbulent mixing may
lead to small, but non-negligible moistening of parcels along time mean trajectories; although not of
primary importance, the latter may be considered as a modifying factor to existing banner clouds.
Page | 154
561
Stratosphere-troposphere exchange (STE) in the vicinity of extra-tropical
cyclones
1
2
2
2
Philipp Reutter , Bojan Skerlak , Michael Sprenger , Heini Wernli
1
2
Institute for Atmospheric Physics, Johannes Gutenberg-University, Mainz, Germany, Institute for
Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
The exchange of air masses across the tropopause plays an important role for the chemical
composition of the stratosphere and troposphere. For instance, the injection of stratospheric air into
the troposphere can enhance the ozone concentration significantly in the troposphere, even down to
the boundary layer. On the other side, the amount of water vapor can be strongly increased when
tropospheric air is transported into the stratosphere.
In this study the importance of Stratosphere-troposphere exchange (STE) is quantified in the vicinity of
extratropical cyclones, based upon climatologies of cyclones and STE. Previous studies estimated the
effects of STE in the vicinity of cyclones through case studies of single cyclones and extrapolated the
results to the global scale. The caveat of this method is the uncertain representativeness of a single
cyclone.
Therefore, we use in this study 30 years of ERA-Interim data to count all STE events in the vicinity of
cyclones. A Lagrangian approach is used to identify STE events from the stratosphere to the
troposphere and vice versa. A sophisticated cyclone identification and tracking tool determines the
exact structure of a cyclone at each time step along its lifecycle. Therefore, an STE event can be
clearly assigned to a specific cyclone.
With this data set we build a climatology of STE events in the vicinity of cyclones and investigate their
spatial and temporal distribution on a global scale and also within a cyclone life cycle. This enables us
to study if STE events happen in preferred areas of a cyclone and during preferred phases of its
lifecycle. Additionally, the climatology allows to determine if the mass flux through the troposphere is
higher when a cyclone is present compared to the geographical mean. Furthermore, we investigate
the relationship between minimum pressure of a cyclone and STE intensity.
Page | 155
202
Extreme South Foehn in Altdorf: a climatology and its relation to large-scale
flow
1
2
3
3
Hilke S. Lentink , Michael Sprenger , Michiel R. van den Broeke , Aarnout J. van Delden , Patrick
4
2
Hächler , Jürg Schmidli
1
2
Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany, ETH Zürich, Institute for Atmospheric
3
and Climate Science, Zürich, Switzerland, University Utrecht, Institute for Marine and Atmospheric
4
Research Utrecht, Utrecht, Netherlands, Swiss Meteorological Institute (MeteoSwiss), Zürich,
Switzerland
South foehn is a North-Alpine lee-wind, potentially causing damage to buildings and nature. Foehn
acts on the meso-scale, has a local character and occurs often during a typical synoptic scale pattern
with southwesterly winds over the Alps. A good understanding of foehn is necessary for reliable
predictions and to give warnings in time, especially for extreme foehn.
This study investigates extreme foehn and the synoptic influence on the foehn process for the first
time. In the presentation, a climatology of extreme foehn for Altdorf, Switzerland, is presented, as well
as an overview of synoptic-scale situations during foehn. According to observational data, most
extreme foehn events occur in winter, and a trend in occurrence or strength over the years is not
found. The synoptic-scale analysis, based on ERA-Interim data, shows the existence of a strong
jetstreak with its exit area above the Alps during extreme foehn. The signal of a jetstreak is robust and
observed in all seasons. The jetstreak location varies from west of the Alps, for short events, to
southwest for longer foehn events.
Page | 156
377
Ice mushrooms of the Patagonian Andes
1
2
Dave Whiteman , Rolando Garibotti
1
2
Atmospheric Sciences, University of Utah, Salt Lake City, United States, Private, El Chalten,
Argentina
The Southern Patagonian Andes are known among mountain climbers for a meteorological
phenomenon that occurs there but is unknown in many other mountain areas. The phenomenon is the
buildup of rime ice in large bulbous or mushroom-shaped accretions on the windward side of
projecting mountain summits, ridges and exposed near-vertical rock faces. These semi-permanent ice
accretions have been called "ice mushrooms", but they have never been investigated scientifically and
are largely unknown to meteorologists. Ice mushrooms are found, for example, on the iconic Cerro
Torre (49.293° S, 73.098° W, 3128 m MSL) in Argentina´s Los Glaciares National Park on the eastern
edge of the Southern Icecap. The mushrooms grow when strong winds accrete super-cooled cloud
droplets onto sub-freezing flow obstacles. The individual rime particles are less dense than solid ice
particles such as hail or sleet and are poorly consolidated into the mushroom. Rime mushrooms are a
hindrance to mountain climbing, as the mushroom surface can be quite unstable. Climbers sometimes
utilize natural near-vertical tunnels that form in the ice, but the origin of the tunnels is still an open
scientific question.
This paper provides an initial scientific definition of ice mushrooms, and considers the meteorological
factors leading to their formation. Southern Patagonia is shown to be a preferred region
geographically, although they also form in other maritime mountain areas. A climatological study using
upper air soundings and the ERA Interim Reanalysis dataset highlights the important role of seasonal
temperature, moisture, cloud and wind distributions. Topographical relief and nearness to large bodies
of cool water also play a role. Local-scale wind dynamics determine where the mushrooms form on a
given mountain massif. The significant challenges that rime mushrooms pose to mountain climbers are
described through photographs and descriptions from Southern Patagonia.
Page | 157
A3.1/A3.2 - ENSO and decadal variability under climate change / Ocean’s role in
climate variability, change, and predictability
09.07.2013 08:15-09:45, Schwarzhorn
708
Multiple influences on equatorial Atlantic variability
1,2
1,2
1
3
3
Ingo Richter , Swadhin Behera , Yukio Masumoto , Bunmei Taguchi , Hideharu Sasaki , Toshio
2
Yamagata
1
Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology,
2
Yokohama, Japan, Application Laboratory, Japan Agency for Marine-Earth Science and Technology,
3
Yokohama, Japan, Earth Simulator Center, Japan Agency for Marine-Earth Science and Technology,
Yokohama, Japan
The equatorial Atlantic hosts a zonal mode of variability that is associated with significant precipitation
anomalies over tropical South America and Africa. Warm and cold events are referred to as Atlantic
Niños and Niñas, respectively, due to their apparent similarity with El Niño-Southern Oscillation
(ENSO) events. Like ENSO, the Atlantic zonal mode is thought to involve a positive feedback
mechanism, in which weakening of the equatorial easterlies, thermocline deepening, and SST
warming mutually reinforce each other.
In the present study we use NCEP reanalysis, a high-resolution OGCM hindcast, and the CSIRO Mk
3.5 coupled GCM to re-examine the dynamics governing Atlantic Niños. We find that equatorial wind
stress forcing and ENSO-like dynamics can explain some of the observed warm events but not all of
them. In particular there are warm events that occur despite easterly surface wind anomalies in the
preceding months. This is due to sub-surface warm anomalies at approximately 5ºN that are advected
toward the equator. The sub-surface warming is ultimately related to SST anomalies in the northern
tropical Atlantic (NTA), which induce wind stress curl anomalies that force downwelling just north of
the equator. This suggests a mechanism by which the NTA SST anomalies can influence the zonal
mode of variability.
Page | 158
116
A unifying perspective on South Atlantic Ocean inter-annual to inter-decadal
climate variability
1,2
1
Hyacinth Nnamchi , Jianping Li
1
State Key Laboratory of Numerical Modelling for Atmospheric Sciences and Geophysical Fluid
2
Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China, Graduate
University of the Chinese Academy of Sciences, Beijing, China
Equatorial Atlantic ocean-atmosphere variability is of great importance for the climates of the nearby
countries, and for the larger-scale, global climate. It is closely linked to the seasonal oscillation of the
inter-tropical convergence zone, monsoonal circulations and climate anomalies over the adjacent
continents. Prevailing theories suggest that the essential mechanism underlying equatorial Atlantic
variability is a dynamical ocean-atmosphere interaction process analogous to the Pacific-based El
Niño Southern Oscillation, and is therefore named Atlantic Niño.
By consensual compositing of independently analyzed historical observations, we show that equatorial
Atlantic variability is consistently phase-locked with an opposite anomaly type in the extra-tropics, off
the Brazil-Uruguay-Argentina coast (r > -0.7). The spatial structure of this phenomenon termed the
South Atlantic Ocean Dipole (SAOD), indicates that unlike El Niño which is focused along the
equatorial belt, the SAOD involves large scale basin-wide changes in sea surface temperature, sea
surface heights, the thermocline, atmospheric circulation and precipitation. Evolution maps of the
SAOD provide a unifying framework for understanding the commonly known modes in the basin
including the Atlantic Niño and Benguela Niño. Based on the consensus of observations, we argue
that solitary equatorial anomaly -as would be expected of “Atlantic Niño”-is a form of systematic error
in numerical models, and show some examples from CMIP3 and CMIP5 models.
Page | 159
743
Interdecadal tendency in atmospheric crculations around the onset of the
western North Pacific summer monsoon
1
1,2
3
Yuta Kuwazuru , Tomohiko Tomita , Tsuyoshi Yamaura
1
2
Graduate School of Science and Technology, Kumamoto University, Kumamoto, Japan, Research
3
Institute for Global Change, JAMSTEC, Yokohama, Japan, Advanced Institute for Computational
Science, RIKEN, Kobe, Japan
The low-frequency variability with periods of interdecadal variations or longer was examined for the
atmospheric circulations associated with the onset of the western North Pacific summer monsoon
(WNPSM). The region of WNPSM, (138˚-160˚E, 15˚-25˚N), is first determined in the western North
Pacific (WNP) as the region with positive values in precipitation difference between the periods before
(mid-July) and after (late July) the WNPSM onset (after - before). The time series analysis is then
performed for the areal mean precipitation rate of the region after removing the linear trend. To extract
the components with periods longer than 11 years, we employed the harmonic analysis and summed
the components of wave numbers 1-3 for the time series of 1979-2010 (32 years).
The low-frequency variability clearly shows the interdecadal tendency concurrent with the Pacific
Decadal Oscillation (PDO) in the North Pacific even in boreal summer. In the first positive phase after
1979, i.e., 1985-93, the WNPSM begins in its own region, while the region shifts westward off the
Philippines in the following negative phase of 1994-2000. In the next positive phase in 2001-07, the
WNPSM is again established in its own region. The positive, negative, and positive SST anomalies in
and around the WNPSM region with the PDO induce such interdecadal tendency in atmospheric
circulations around the WNPSM onset.
The linear trend removed shows a tendency that the precipitation before the WNPSM onset increases,
while it after the onset is almost unchanged in and around the WNPSM region. The similar tendency is
identified in the tropical cyclone activity: it is stronger before the onset. It is confirmed that the onset of
WNPSM has been unclear during the latest few decades.
Page | 160
789
The decadal variability of the heat and freshwater content of the subpolar North
Atlantic
1
1
1
Claus Böning , Markus Scheinert , Arne Biastoch , Erik Behrens
1
GEOMAR, Kiel, Germany
1
During the last five decades striking changes occurred in the freshwater and heat content of the
subpolar North Atlantic (SNA). The deep and abyssal waters that originate in this region to feed the
lower limb of the AMOC experienced a remarkable decrease in salinities after the late 1960s, linked to
a progressive dilution of the system of overflows from the Nordic Seas. A rapid reversal of the
freshening trend occurred in the mid-1990s, with a pronounced salinification especially in the eastern
SNA; at the same time, the freshening of the overflows slowed to a stop. An intriguing feature of the
observational record is the tight co-variability of the freshwater and heat content of the SNA: the longterm freshening was accompanied by a progressive decrease in heat content, and both trends
reversed simultaneously after 1995. Here we use a sequence of experiments with high-resolution
(1/4°, 1/12°, and 1/20°) ocean-sea ice models to identify the dynamical causes of these decadal
changes. Hindcast simulations of the oceanic response to the atmospheric variability 1948-2007
capture the decadal variability in the integral properties of the SNA as reconstructed from historical
salinity and temperature data, and reproduce pertinent observational indices of mid-latitude circulation
variability. Analysis of the freshwater and heat budgets shows that the largest contribution to the SNA
property changes has been due to variations in the inflow of warm, saline water with the subtropical
North Atlantic, with only a minor contribution due to variations in the inflow of cold, fresh waters from
the northern basins. The subtropical-subpolar flux variability is not directly related to the AMOC; it can
conceptually be understood in terms of the “intergyre-gyre” response to the mid-latitude westerlies
associated with the NAO.
Page | 161
593
The GloSea5 ocean analysis: a re-analysis for 1989-2012
1
1
1
1
1
Drew Peterson , Matthew J. Martin , Jennifer Waters , Matthew D. Palmer , Chris D. Roberts , Daniel
1
1
Lea , James While
1
UK Met Office, Exeter, United Kingdom
As a requirement for the initialization of the historical forecast component of the GloSea5 high
resolution (~50km atmos/~25km ocean) seasonal forecast system, an ocean analysis for 1989-present
has been undertaken at the UK Met Office (UKMO). Except for ocean surface boundary conditions,
this analysis is identical to the latest UKMO Forecast Ocean Assimilation Model (FOAM-V2) also
recently implemented at UKMO, using the NEMO V3.2 ocean model, the CICE VN4.1 sea ice model,
and NEMOVAR (3DVAR) data assimilation.
This analysis has been put forward as the UKMO contribution to the GSOP/GODAE ocean synthesis
project. Initial findings of the system indicate the analysis shows a good representation of the ocean
and sea ice mean state and temporal variability, including that of the Atlantic meridional overturning
circulation (AMOC) and northward heat transport.
This presentation will describe the system used to generate the reanalysis and show a sample of the
results, including comparisons to independent data from the RAPID AMOC array at 26N.
Page | 162
933
Influence of volcanic eruptions on bi-decadal variability of the North Atlantic in
historical, initialised simulations and observations
1
2,3,4
2
Didier Swingedouw , Juliette Mignot , Eric Guilyardi
1
2
3
LSCE/IPSL, Paris, France, LOCEAN/IPSL, Paris, France, Climate and Environmental Physics,
4
Physics Institute, Univ Bern, Bern, Switzerland, Oeschger Centre for Climate Change Research,
University of Bern, Bern, Switzerland
Multi-decadal variability of the North Atlantic is analysed with a focus on the bi-decadal oscillations.
Indeed, Greenland isotopes exhibit significant variability at this 20-year time scale over the last
millennium, suggesting the existence of a preferential mode of variability at this time scale in the North
Atlantic sector. We focus our analysis on the impact of volcanic eruptions on such an internal bidecadal variability, which also exists in the IPSL-CM5A model. For this purpose we examine
simulation from this model with historical forcing and/or initialisation through simple SST nudging over
the last 60 years. We find that volcanic eruptions reset the bi-decadal cycle in the North Atlantic
around 15 years after the beginning of the eruption. In order to explore the impact produced by the
successive eruptions from Mount Agung, El Chichon and Pinatubo, we propose a conceptual model
that we compare with an ensemble of sensitivity experiments using IPSL-CM5A, where Pinatubo
eruption is removed. We find similar behaviours for the simulated overturning circulation and the one
deduced from the conceptual model, showing that the essence of the process in the model is well
captured by the simple conceptual model. In particular it appears that Pinatubo eruption leads to a
destructive interference with previous volcanoes, since erupting 9 years and 28 years after the El
Chichon and Mount Agung. After this eruption, bi-decadal variability thus tends to be damped. Finally,
in order to evaluate the realism of the mechanisms proposed, we compare the simulated variability
with recent long-term compilations over the last century of SST and SSS in the subpolar gyre from
Reverdin et al. (2010).
Page | 163
B1.1a - Advanced methods in data assimilation and ensemble forecasting
09.07.2013 08:15-09:45, Seehorn
399
Exploring multi-scale and model-error treatments in ensemble data
assimilation
1,2,3
1,4
1
1,5
Takemasa Miyoshi , Juan J. Ruiz , Shigenori Otsuka , Keiichi Kondo
1
Data Assimilation Research Team, RIKEN Advanced Institute for Computational Science, Kobe,
2
Japan, Atmospheric and Oceanic Science, University of Maryland, College Park, United States,
3
4
Earth Simulator Center, JAMSTEC, Yokohama, Japan, University of Buenos Aires, Buenos Aires,
5
Argentina, University of Tsukuba, Tsukuba, Japan
Ensemble data assimilation methods have been improved consistently and have become a viable
choice in operational numerical weather prediction. A number of issues for further improvements have
been explored, including flow-adaptive covariance localization and advanced covariance inflation
methods. Dealing with multi-scale error covariance and model errors is among the unresolved issues
that would play essential roles in analysis performance. With higher resolution models, generally
narrower localization is required to reduce sampling errors in ensemble-based covariance between
distant locations. However, such narrow localization limits the use of observations that would have
larger-scale information. Previous attempts include successive covariance localization by F. Zhang et
al. who proposed applying different localization scales to different subsets of observations. The
method aims at using sparse radiosonde observations at a larger scale, while using dense Doppler
radar observations at a small scale simultaneously. This study aims at separating scales of the
analysis increments, independent of observing systems. Inspired by M. Buehner, we applied two
different localization scales to find analysis increments at the two separate scales, and obtained
astonishing improvements at all scales in simulation experiments using an intermediate AGCM known
as the SPEEDY model. Another important issue is about the model errors. Among many other efforts
since Dee and da Silva's model bias estimation, we explore a discrete Bayesian approach to
adaptively choosing model physics schemes that produce better fit to observations. Also, traditional
state-augmentation approach to model parameter estimation has been explored. This presentation
summarizes our recent progress at RIKEN on these theoretical and practical topics for further
improvement of ensemble data assimilation approaches.
Page | 164
1041
A comparison of Ensemble-Variational data assimilation and 4D-Var for global
deterministic weather prediction
1
1
Mark Buehner , Josée Morneau , Cécilien Charrette
1
Environment Canada, Montreal, Canada
1
A new approach, called Ensemble-Variational data assimilation (EnVar), is tested and compared with
the Canadian operational global atmospheric 4D-Var. The EnVar approach relies on the fourdimensional ensemble-based background error covariances produced by the ensemble Kalman filter
(EnKF) and a variational minimization to produce a single deterministic analysis. It is well-suited for
producing the high-resolution analyses required to initialize global deterministic medium-range
forecasts because: 1) it can efficiently assimilate the very large volume of observations currently
available, 2) it is more computationally efficient than 4D-Var, and 3) it is more flexible with respect to
modelling the background error covariances than traditional EnKF approaches. Verification results
from using EnVar with covariances obtained by averaging the EnKF-based and traditional NMCmethod-based covariances will be shown. These results will be compared with those obtained from
the standard 4D-Var (and 3D-Var) approaches. Additional experiments were performed to assess the
accuracy and importance of including the temporal dimension within the assimilation window in the
ensemble covariances.
Page | 165
360
Research on ensemble-variational data assimilation at the Met Office
1
Stephen Pring
1
Met Office, Devon, United Kingdom
The Ensemble-Variational Data Assimilation technique is a method which relies heavily on the
ensemble members to create the analysis for the next forecast. The Ensemble-Variational method is a
possible future technique for performing Data Assimilation at the Met Office and in this talk we shall
present research results of the scheme. We compare the method with existing DA methods including
hybrid-3DVar, 4DVar and hybrid-4DVar, with hybrid-4DVar being the current operational method at the
Met Office. We will consider the effect of the number of ensemble members on the scheme and some
of the characteristic features of the method. We also show differences in the performance of the
scheme between the Northern and Southern Hemisphere and results of the use of waveband filtering.
Page | 166
410
A prediction scheme for nonautonomous unstable systems with determining
variables
1
2
Paul Krause , Pedro L.S. Dias
1
2
Mathematics, Universidade Federal de Santa Catarina, Florianópolis, Brazil, Atmospheric Sciences,
Universidade de São Paulo, São Paulo, Brazil
Instability is in the nature of most nonlinear processes toward equilibrium of fluid mechanical systems.
The time averaging of sample values or use of asymptotic methods (e.g. BV) may be a resort to
greater robustness with respect to sample size in predictions, but these methods are only amenable to
coarse scales and, for asymptotic methods, to autonomous systems in principle. In this talk a novel
sampling method, the Influence Sampling - Monte Carlo (ISMC) scheme, is presented for predictions
with nonautonomous unstable systems possessing a group of variables, referred to as determining
variables, that whenever continuously controlled with a true history leaves the remaining system with a
contractive dynamics. The method relies in the derivation of a short-time empirical influence function
for the dynamics of a group of variables of an o.d.e. model (in robust statistics, an empirical influence
function measures the sensitivity of an estimator, the o.d.e. model dynamics in this case, with respect
to perturbations in the sample values). Prediction tests are conducted on the ISMC scheme with the
L63 and L63+ systems of o.d.e., the latter being a nonautonomous perturbation of the L63 system with
sine functions. The ISMC predictions with the L63 system show a nonexponential growth of the
sample standard deviation, thus to have more memory than the Monte Carlo predictions with it, the
longer memory the less uncertain the parameter values in the model.
Page | 167
B7.3a - Atmosphere and UT/LS Interactions
09.07.2013 08:15-09:45, Sertig
1223
Global stratospheric mean age of air and its temporal variation from MIPAS
SF6 observations
1
1
1
1
2
Gabriele Stiller , Thomas von Clarmann , Florian Haenel , Ellen Eckert , Bernd Funke , Norbert
1
1
1
1
1
1
Glatthor , Udo Grabowski , Sylvia Kellmann , Michael Kiefer , Andrea Linden , Stefan Lossow ,
2
Manuel Lopez-Puertas
1
Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Eggenstein2
Leopoldshafen, Germany, Instituto de Astrofisica de Andalucia (IAA), CSIC, Granada, Spain
Monthly zonal means of mean age of air has been derived from global SF6 distributions measured by
MIPAS/Envisat, binned at 10° latitude and 1-2 km altitude. The SF6 distributions have been
transformed to mean age of stratospheric air by applying a Wald function-shaped age spectrum. The
10-years time series of global age of air has been analyzed regarding its short-term variations
(seasonal, semi-annual, QBO), and its decadal behavior. The impact of subsidence of mesospheric
SF6-depleted air and in-mixing into non-polar latitudes on mid-latitudinal absolute age of air and its
linear increase has been quantified.
The derived linear trends of age of air were found to be inhomogeneous over the globe, with
increasing age of air in Northern mid-latitudes and middle-stratospheric tropics, and decreasing age of
air in the tropical lowermost stratosphere and larger parts of the Southern mid-latitudes. The global
trend pattern will be compared to that of other transport tracers measured by MIPAS. Analysis of the
amplitudes and phases of the seasonal variation shed light on the coupling of stratospheric regions to
each other. In particular, the Northern mid-latitude stratosphere is well coupled to the tropics, while the
Northern lowermost mid-latitudinal stratosphere is decoupled, confirming the separation of the shallow
branch of the Brewer-Dobson circulation from the deep branch. The observational data will be
interpreted in terms of a acceleration/deceleration of the Brewer-Dobson circulation and discussed in
context with recent published atmospheric model results.
Page | 168
1256
Recent results from OSIRIS measurements of the UTLS
1
1
1
1
1
1
Doug Degenstein , Adam E. Bourassa , Chris Sioris , Cristen Adams , Landon Rieger , Nick Lloyd ,
2
Chris McLinden
1
Institute of Space and Atmospheric Studies, University of Saskatchewan, Saskatoon, Canada,
2
Environment Canada, Toronto, Canada
The Canadian built OSIRIS instrument has been in operation onboard the Swedish spacecraft Odin
since the autumn of 2001. Recently it has become apparent that instruments like OSIRIS and
SCIAMACHY that measure spectrally dispersed limb scattered for the purpose of retrieving vertical
profiles of atmospheric constituents can add important insight into processes present within the UTLS.
This paper will highlight the quality of the OSIRIS ozone and sulphate aerosol data within the UTLS
through a description of some recent studies and the important results of these studies. In particular
recent tropical upper tropospheric and lower stratospheric ozone trend analysis will be presented.
Also, a new retrieval algorithm for sulphate aerosol will be presented. This retrieval algorithm, that
more accurately retrieves particle size parameters, will remove some small systematic biases currently
found within the OSIRIS aerosol product thus improving the utility of the data product for trend
analysis.
Page | 169
1239
Bromine chemistry of the lower stratosphere: current issues
1
Björn-Martin Sinnhuber
1
Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany
Bromine plays an important role in catalytic ozone loss of the lower stratosphere. A significant fraction
of the stratospheric bromine loading presumably originates from biogenic emissions of very short lived
source gases (VSLS). Progress has been made in recent years in quantifying the contribution of VSLS
to the stratospheric bromine loading and in detecting trends in stratospheric bromine over the past one
or two decades. However, still little is know if and how the biogenic contribution to stratospheric
bromine will change in a changing climate with possible changes in emission strengths, transport
pathways and chemical conditions. Here I will present recent results from process modelling and
chemistry climate modelling on the role of bromine - and in particular VSLS - in lower stratospheric
ozone chemistry.
Page | 170
C4.1a - Meteorological forcing data and distributed modelling of snow, ice and
hydrology in mountain watersheds
09.07.2013 08:15-09:45, Sanada I
469
Spatial interpolation in complex terrain: a suite of gridded climate datasets for
Switzerland
1
Christoph Frei
1
Federal Office of Meteorology and Climatology MeteoSwiss, Zurich, Switzerland
In complex terrain the construction of meteorological forcing fields for distributed modelling is
confronted with major challenges: Spatial variability of parameters is high, representativity of
measurements limited, and measurement networks are generally biased. In this presentation an
overview will be given of a suite of gridded climate datasets for the territory of Switzerland, including a
sector of the Alpine mountain chain. The datasets encompass three parameters (temperature,
precipitation and sunshine duration), exhibit a grid-spacing of 2 kilometers and expand over a 50-year
period (1961-2010) at daily time resolution. The interpolation methods used for the construction of
these datasets were designed individually for each parameter and, where possible and meaningful,
they also integrate information from satellites and radar as a complement to station data. The
presentation will illustrate these methodological developments and demonstrate their working at hand
of challenging example cases. Results from a detailed evaluation will be used to discuss the limitations
of the datasets in applications. This also pinpoints to issues of scale and long-term consistency that
require consideration when using grid datasets in distributed modelling and climate monitoring. The
gridded datasets of MeteoSwiss are regularly updated and are available, free of charge for research.
Page | 171
545
Interpolation and downscaling of precipitation and temperature in complex
terrain with the analysis tool VERA
1
1
Dieter Mayer , Reinhold Steinacker
1
Department of Meteorology and Geophysics, University of Vienna, Vienna, Austria
Analyzing meteorological variables from irregular distributed stations to a regular grid in complex
terrain is still challenging. A lot of different physical processes of many scales cause a high spatial and
temporal variability, that can be observed especially for precipitation and temperature fields - two of
the most important input variables for models concerning the accumulation or ablation of snow.
The analysis tool VERA (Vienna Enhanced Resolution Analysis), developed at the department of
Meteorology and Geophysics at the University of Vienna, is focusing on the interpolation and
downscaling of meteorological observations in complex terrain. The special approach of VERA is to
split observations into explained and unexplained components whereas the unexplained components
are considered to be smooth and the explained parts consist of predefined patterns or gridded
observations (Fingerprints) that are weighted by the analysis procedure. Both, the smoothness of the
unexplained part and the difference between observations and analyses, are taken into account by
minimizing a cost function.
Fingerprint patterns take into account the thermal and dynamical effects, topography has on
temperature and pressure fields, as well as dependencies of precipitation sums on height and luv-lee
effects. Although afflicted with several limitations, Radar information can be used to improve
precipitation analyses.
The focus of the presentation is drawn to the computation of vertical precipitation and - in order to
estimate the snow line - of temperature profiles. For the latter, temperature and pressure fields have to
be analyzed for the surface and some additional levels. It is shown, how temperature and pressure
values at these levels can be used to obtain vertical temperature profiles consisting of piecewise
defined polynomials taking into account atmospheric inversions. As a consequence, VERA is able to
analyze precipitation amounts, fallen as snow or rain, separately.
Page | 172
810
Local vs. regional controls in the alpine area: lessons learned from
geostatistical mapping of the surface air temperature
1
2
3
1
Isabella Zin , Thierry Lebel , Eric Jabot , Charles Obled
1
2
3
LTHE/Université de Grenoble, Grenoble, France, LTHE/IRD, Grenoble, France, LTHE/CNRS,
Grenoble, France
Air temperature represents a key parameter for snow, ice and hydrological models in alpine regions,
as it controls the rain-snow line location and the snow/ice accumulation and melting. High-resolution
temperature fields are needed as input of distributed hydrological modeling in mountain areas,
preferably at sub-daily time steps, in order to account for the diurnal cycle. The estimation of such
temperature fields is challenging due to the spatial and temporal variability of environmental lapse
rates (ELR) associated to complex topography. In this study, 10 years (2000-2009) of data from about
200 French, Italian and Swiss temperature stations were used in order to calculate surface air
temperature gradients at 0, 6, 12 and 18 hr UTC over a window of 71500 km2 centered on the French
Northern Alps. Firstly, the spatial and temporal variability of these gradients was analyzed across
scales, in particular with regards to the weather circulation patterns. Then, different kriging methods
were tested for interpolating temperature fields over a 1-km resolution grid, using both elevation and
solar radiation as external drift, with ELR calculated at regional or local scale, using climatological
(constant) or time-dependent variograms. Prediction errors were estimated in terms of mean absolute
error, root mean square error and kriging standard deviation. Essentially because of frequent
inversions during winter and/or night-time, interpolated temperature fields are globally more reliable in
summer and daytime. Considering the spatio-temporal variability of ELR improves significantly the
kriging performance. Nevertheless, variograms display generally a strong nugget effect, meaning that
there is a large local variance that is not captured by our network of stations. This implies that there is
hardly any continuity between the 1-10-km scale and the smaller ones, which might prove that our
'regionalized variable' framework is probably not well suited go below the 1-km scale for detailed
snow-hydrology studies.
Page | 173
609
A combined topography and climate pre-processor to drive high-resolution
land surface models in complex terrain
1
1
Joel Fiddes , Stephan Gruber
1
Department of Geography, University of Zurich, Zurich, Switzerland
Numerical simulations of land-surface processes are important to perform landscape-scale
assessments of earth-systems. This task is problematic in complex terrain due to: (i) high resolution
grids required to capture strong lateral variability, (ii) lack of meteorological forcing data where it is
required. To address this problem we have developed an efficient two-part tool, which is designed for
use with numerical land surface models (LSM) driven by gridded climate datasets, in complex terrain.
(1) TopoSUB is a surface pre-processor designed to sample a fine-grid domain (LSM grid/DEM) along
important topographical (or other) dimensions through a clustering scheme, allowing the construction
of a lumped model that represents the main sources of fine-grid variability. We can then apply a 1-D
LSM efficiently over large areas. Results can be presented as summary statistics, or spatialised to
original fine-grid resolution (using membership functions) to retrieve a high-resolution surface of the
4
target variable. The ability of TopoSUB to approximate results simulated by a distributed LSM at 10
less computations is demonstrated by comparison of 2-D and lumped simulations.
(2) TopoSCALE scales coarse-grid climate fields to fine-grid topography using pressure level data,
which provides a good description of the atmospheric column. It also applies necessary topographic
corrections e.g. required for radiation fields. This provides the driving fields to the LSM. Tested against
ground data, this scheme has been shown to improve the scaling and distribution of meteorological
parameters in complex terrain, as compared to conventional methods, e.g. lapse-rate approaches.
This tool allows for applications of LSMs over large areas of complex terrain, especially in data poor
regions. Benefiting from high density of measured data, the method has been tested in the European
Alps, but is readily adapted to other regions/fields of application in terms of input data, dimensions of
variability, choice of LSM.
Page | 174
802
Comparison of statistical and dynamical approaches for the rain-snow line
localization in the Alps
1
2
1
2
Matthias Latapie , Ingrid Dombrowski-Etchevers , Isabella Zin , Louis Quéno , Stéphanie Froidurot
1
LTHE, UMR 5564 (CNRS-Grenoble INP-IRD-UJF), Université de Grenoble, Grenoble, France,
2
Meteo-France, CNRM/GAME UMR3589, Centre d'Études de la Neige, Grenoble, France
1
The rain-snow line location is of importance for snow, ice and hydrological studies in regions with
complex mountain topography and is still a modeling challenge. We focus here on flood forecasting in
alpine area, where the dynamics of river flows is highly dependent on the dynamics and the spatial
variability of snow covered areas. Within this framework, a good forecast of the precipitation phase
(liquid or solid) is needed, as liquid precipitation will rapidly contribute to river outflow (eventually, in
addition to snowmelt), whereas solid precipitation will be stored until melting occurs later on. In this
study, three different approaches are compared and evaluated, in order to assess the uncertainty on
short term (up to 24 hours) forecasting of the rain-snow line, considering a window of about 100 000
km2 centered over the French Alps. Outputs from statistical and dynamical models are analyzed. The
first approach provides the probability of rain or snow by means of a logistic regression model making
use of low resolution forecasts of surface temperature and relative humidity issued from the ARPEGE
model. With the second approach, the precipitation phase is a direct output of the mesoscale nonhydrostatic numerical weather forecast model AROME at 2.5 km resolution. Finally, the temperature
and humidity fields forecasted by AROME are used as input of the same logistic regression model
used at low resolution for identifying the rain-snow line location. The three approaches are firstly
evaluated over the period 2009-2011 and at sub-daily time steps by comparison with available
observations of present weather types. Different criteria derived from the resulting confusion matrix are
used for this quantitative evaluation, such as the critical success index CSI and the percent of
misclassified PM. Then, at regional scale, the sensitivity of the rain-snow line localization to the three
different forecasting methods is discussed.
Page | 175
B4.1a - Global monsoon system: past, present and future
09.07.2013 08:15-09:45, Aspen I
1024
Aspects of global and regional monsoons
1
Brian Hoskins
1
Grantham Institute for Climate Change, Imperial College London, London, United Kingdom
A review will be given of some of our basic understanding of global and regional monsoons. This will
be used as a basis for consideration of the characteristics of current monsoons and results from
climate projections on how these characteristics may change in a changing climate.
Page | 176
436
Monsoons in a changing world: a regional perspective in a global context
1
1
2
3
4
Akio Kitoh , Hirokazu Endo , K. Krishna Kumar , Iracema F.A. Cavalcanti , Prashant Goswami ,
5
Tianjun Zhou
1
2
3
4
MRI, Tsukuba, Japan, IITM, Pune, India, CPTEC, Cachoeira Paulista, Brazil, C-MMACS,
5
Bangalore, India, LASG/IAP, Beijing, China
We provide a latest view of global as well as regional monsoonal rainfall and their changes in the 21st
century under RCP4.5 and RCP8.5 scenarios as projected by 29 CMIP5 climate models. The global
monsoon area defined based on the annual range in precipitation will expand mainly over the central
to eastern tropical Pacific, the southern Indian Ocean, and eastern Asia. The global monsoon
precipitation intensity and the global monsoon total precipitation will increase, resulting in remarkable
increase in monsoon-related precipitation. Indices of heavy precipitation are projected to increase
much more than that for the mean precipitation. Over the Asian monsoon domain, projected changes
in extreme precipitation indices are larger than that over other monsoon domains, indicating that the
sensitivity of Asian monsoon to global warming is stronger than that of other monsoons. Over the
American and African monsoon regions, projected future changes in mean precipitation are rather
modest, but those in precipitation extremes are large. As for the seasonality, the monsoon retreat
dates will delay, while the onset dates will either advance or show no change, resulting in lengthening
of the monsoon season. However, models ability in reproducing the present monsoon climate and
large scatter among the model projections limit the confidence on the results. The increase of the
global monsoon precipitation can be attributed to the increase of moisture convergence due to
increased surface evaporation and water vapor in the air column though offset to a certain extent by
the weakening of the monsoon circulation.
Page | 177
724
Recent change of the global monsoon precipitation
1
2
3
4
1
Bin Wang , Jian Liu , Hyung-Jin Kim , Peter J. Webster , So-Young Yim
1
2
University of Hawaii, Honolulu, United States, Nanjing Institute of Geography and Limnology,
3
Nanjing, China, Japan Agency for Marine-Earth Science and Technology, Yohohama, Japan,
4
Georgia Institute of Technology, Atlanta, United States
The global monsoon (GM) is a defining feature of the annual variation of Earth´s climate system.
Quantifying and understanding the present-day monsoon precipitation change are crucial for
prediction of its future and reflection of its past. Here we show that regional monsoons are coordinated
not only by external solar forcing but also by internal feedback processes such as El Nino-Southern
Oscillation (ENSO). From one monsoon year (May to the next April) to the next, most continental
monsoon regions, separated by vast areas of arid trade winds and deserts, vary in a cohesive manner
driven by ENSO. The ENSO has tighter regulation on the northern hemisphere summer monsoon
(NHSM) than on the southern hemisphere summer monsoon (SHSM). More notably, the GM
precipitation (GMP) has intensified over the past three decades mainly due to the significant upward
trend in NHSM. The intensification of the GMP originates primarily from an enhanced east-west
thermal contrast in the Pacific Ocean, which is coupled with a rising pressure in the subtropical
eastern Pacific and decreasing pressure over the Indo-Pacific warm pool. While this mechanism tends
to amplify both the NHSM and SHSM, the stronger (weaker) warming trend in the NH (SH) creates a
hemispheric thermal contrast, which favors intensification of the NHSM but weakens the SHSM. The
enhanced Pacific zonal thermal contrast is largely a result of natural variability, whilst the enhanced
hemispherical thermal contrast is likely due to anthropogenic forcing. We found that the enhanced
global summer monsoon not only amplifies the annual cycle of tropical climate but also promotes
directly a "wet-gets-wetter" trend patterns and indirectly a "dry-gets-drier" trend pattern through
coupling with deserts and trade winds. The mechanisms recognized in this study suggest a way
forward for understanding past and future changes of the GM in terms of its driven mechanisms.
Page | 178
1243
Climate change and the South Asian monsoon
1
2
Andrew Turner , H Annamalai
1
2
NCAS-Climate, University of Reading, Reading, United Kingdom, IPRC, SOEST, University of
Hawaii, Manoa, United States
The vagaries of South Asian summer monsoon rainfall on short and long timescales impact the lives of
more than one billion people. Understanding how the monsoon will change in the face of global
warming is a challenge for climate science, not least because our state-of-the-art general circulation
models still have difficulty simulating the regional distribution of monsoon rainfall. However, we are
beginning to understand more about processes driving the monsoon, its seasonal cycle and modes of
variability. This gives us the hope that we can build better models and ultimately reduce the
uncertainty in our projections of future monsoon rainfall. This presentation of our recent review paper
examines the uncertainty in recent trends in observations of monsoon rainfall for recent decades and
discusses possible causes, as well as looking at their projections into the future in the context of
continuing decadal variability. We also discuss projections of interannual and intraseasonal modes of
monsoon variability and rainfall extremes.
Page | 179
A4.2b - Sea ice and Ocean-Atmosphere Interactions
09.07.2013 10:15-11:45, Sanada II
210
Atmospheric circulation responses to Arctic sea ice loss
1
1
1
Ruth Petrie , Len Shaffrey , Rowan Sutton
1
Department of Meteorology, NCAS-Climate, University of Reading, Reading, United Kingdom
The Arctic is warming at a rate greater than the global mean temperature increase, this has
contributed to the reduction in Arctic sea ice cover. Arctic sea ice cover has been reducing at an
accelerated rate over the past decade and the lowest ever recorded ice extent was in September
2012. The reduction in sea ice cover increases the amount of absorbed shortwave solar radiation. This
increased energy is transferred from the ocean to the atmosphere during the Autumn during the ice
growth season, this in turn further warms the Arctic atmosphere.
The purpose of this study is to understand how the Artic atmosphere might have responded to the
recent decline in sea ice cover, to investigate how these local changes may affect more remote
locations through large-scale changes in the atmospheric circulation and to identify what feedback
processes may be involved.
This presentation will show the results of GCM experiments where annually repeating cycles of sea ice
and sea surface temperature (SST) are prescribed in atmosphere only experiments using the Met
Office climate model, HadGEM3 (N96L85). A reference period of 1996-2005 is used in the control
experiment and the perturbation period is defined to be from 2007-2011. In the perturbation period
ERA-Interim reanalysis data show that the Eurasian Arctic is anomalously warm in Spring and that
there are distinct circulation anomalies in Summer. This study aims to understand the thermal
response in all seasons and the circulation response in Spring and Summer in particular.
Page | 180
747
North America surface temperature and precipitation response to Arctic sea ice
variability
1
2
3
Yinghui Liu , Yafang Zhong , Jeffrey R. Key
1
2
University of Wisconsin-Madison, Madison, United States, Center for Climate Research, UW3
Madison, Madison, United States, Center for Satellite Applications and Research, NOAA, Madison,
United States
The unprecedented Arctic sea ice retreats in recent decade have consequences for the atmospheric
temperature, moisture, and vertical structure, which might in turn influence the weather and climate in
the mid-latitude by modulating large-scale circulations. However, to what amplitude and how the Arctic
sea ice changes impact the weather and climate in the Arctic and in the mid-latitude are unclear. In
this study, we investigate the response of North America surface temperature and precipitation to the
variability in Arctic sea ice extent using statistical analysis tools, including EOF analysis, generalized
equilibrium feedback analysis (GEFA), and correlation analysis. Observational data, e.g. the passive
microwave sea ice concentration in the Arctic, University of Delaware air temperature and
precipitation, and U.S. climate extremes index (CEI), from 1978-2008 are used.
EOF analysis of Arctic sea ice concentration reveals distinct variability modes in four seasons. The
GEFA analysis suggests a season-dependent linkage of Arctic sea ice variability to the North America
climate while examining the surface temperature and precipitation response to these leading sea ice
modes. For example, the sea ice retreat in the Pacific side of the Arctic is associated with anomalous
warmth in the U.S. west and anomalous coldness in the upper Midwest in autumn, whereas the sea
ice retreat over the Barents and Kara Seas in spring favors anomalous wetness in the Alaska and
north Canada. Note that these GEFA responses are free of the effect of leading sea surface variability
modes in a linear framework. Correlation analysis of the leading Arctic sea ice modes and U.S. CEIs
also indicates an association of the leading sea ice modes and the extreme wet conditions in the U.S.
in winter and spring These findings will serve as an observational benchmark in studying the dynamic
pattern response on the Arctic sea ice changes.
Page | 181
791
Investigating the link between Barents Sea ice and cold Siberian winters
1
2
2
2
Svetlana Sorokina , Justin Wettstein , Camille Li , Nils Gunnar Kvamstø
1
G. C. Rieber Climate Institut, Nansen Environmental and Remote Sensing Center and Bjerknes
2
Centre for Climate Research, Bergen, Norway, Geophysical Institute, University of Bergen and
Bjerknes Centre for Climate Research, Bergen, Norway
Recent Barents Sea ice loss has been implicated in forcing atmospheric responses associated with a
warm-Arctic cold-Siberia (WACS) pattern created by altered heat flux exchanges between the surface
ocean and the atmosphere.
Here, we investigate the nature of the link between Barents Sea ice cover and the atmosphere by
focusing on turbulent heat fluxes (THF) in the winter season (DJF) using reanalysis data (1979-2012).
The leading pattern (EOF1: 33 %) of Barents Sea THF variability during winter has a broad spatial
signature over the entire Barents Sea region and is only weakly related to sea ice cover, while the
second pattern (EOF2: 20 %) is strongly related to Barents Sea ice changes, exhibiting a dipole
structure straddling the ice edge.
The surface temperature signatures of EOF1 and EOF2 are similar and resemble the WACS pattern,
with associated sea level pressure anomalies indicating southerly flow and warm air advection over
the Barents Sea region. The fact that EOF1 shows negative THF anomalies (reduced ocean-toatmosphere heat loss), coincident with stronger surface air temperature and weaker sea surface
temperature warming, suggests that atmospheric circulation variability contributes substantially to the
surface warming and the THF anomalies in the Barents Sea.
Additional analyses on individual winter months and using a WACS-based index provide further
support for the importance of the atmospheric circulation.
These results suggest that atmospheric variability plays an important role in driving observed
variability in Barents Sea THF, ice cover, as well as out-of-phase temperature fluctuations between the
Barents Sea and Siberia. This is in some degree of contrast to previous studies on the link between
Barents Sea ice and the WACS pattern that have described the relationship as fundamentally the
result of the atmosphere responding to Barents Sea ice.
Page | 182
254
Drivers of drift-speed variations in Arctic sea ice
1
1
Einar Olason , Dirk Notz
1
Max Planck Institute for Meteorology, Hamburg, Germany
In this presentation we show that most of the observed variations in mean sea-ice drift speed in the
Arctic are related to variations in sea-ice concentration. Our analysis is primarily based on buoy data
for drift speed, satellite observations of sea-ice concentration, submarine observations of ice thickness
and reanalysis data for surface wind speed. We consider two main modes of drift speed variations:
The long term trend and seasonal changes. We show that the observed seasonal cycle of drift speed
is mostly due to changes in sea-ice concentration. The long term trend is also shown to be due to a
long term trend in concentration and is only significant in months where concentration is already
relatively low. Finally we show that the observed increase in drift speed in months of low concentration
is realised because the ice is responding more readily to the synoptic scale forcing. The increase in
drift speed is therefore primarily caused by an increase in the mobility of the ice cover, and not by a
strengthening of the large-scale circulation. The importance of synoptic scale forcing also means that
comparison with models using monthly average velocities may not be accurate.
Page | 183
151
The impact of heterogeneous surface temperatures on the 2-m air temperature
over the Arctic Ocean
1
1
2
3
4
Amelie Tetzlaff , Christof Lüpkes , Lars Kaleschke , Felix Ament , Timo Vihma
1
2
Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany, Institute of
3
Oceanography, University of Hamburg, Hamburg, Germany, Institute of Meteorology, University of
4
Hamburg, Hamburg, Germany, Finnish Meteorological Institute, Helsinki, Finland
Air-ice-sea interactions have a large impact on the temperatures of the Arctic atmospheric boundary
layer. We investigate the influence of spatial surface temperature changes over the Arctic Ocean on
the 2-m air temperature variability using backward trajectories based on ERA-Interim and the JRA25
wind fields. They are initiated at Alert, Barrow and at the Tara drifting station. We use a simple
Lagrangian box model which only includes the effect of sensible heat fluxes to calculate the
temperature evolution along the trajectories. The calculations are based on MODIS ice surface
temperatures and four different sets of ice concentration derived from SSM/I and AMSR-E data.
Modeled temperatures, mean ice surface temperatures and sensible heat fluxes along the trajectories
are correlated with the in situ temperatures at the stations. Under nearly cloud free conditions, up to 90
% of the 2-m air temperature variance can be explained for Alert and 70 % for Barrow using these
methods. These results are robust for the different sets of reanalyses and ice concentration data.
Trajectories based on 10-m wind fields from both reanalyses show large spatial differences in the
Central Arctic, which leads to differences in the correlations between modeled and observed 2-m air
temperatures. They are most pronounced at Tara where explained variances amount to 70 % using
JRA and 80 % using ERA. The results also suggest that near-surface temperatures at a given site are
influenced by the variability of surface temperatures in a domain of about 200 km radius around the
site.
Page | 184
C6.3 - Avalanche flow dynamics
09.07.2013 10:15-11:45, Aspen II
187
Deducing the size and velocity of avalanches from radar, seismic and
infrasound data at Vallée de la Sionne
1
2
2
3
Cristina Perez Guillen , Betty Sovilla , James N. McElwaine , Emma Suriñach
1
2
Geodinámica y Geofísica, University of Barcelona, Barcelona, Spain, Research Unit Avalanches and
3
Prevention WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland, University of
Barcelona, Barcelona, Spain
Snow avalanches are extended sources of seismic and infrasonic waves. Recent studies have shown
that the interaction between the dense core of an avalanche and the basal surface is the main source
of the seismic signal, whereas the suspended powder cloud and the dilute layer are the main sources
of infrasound. These sensors thus give complementary information about the characteristics of an
avalanche and can, in theory, be used to deduce avalanche speed, location and size as functions of
time. In practice however this is very difficult because accurate models are needed for source
generation and wave propagation and these models must be validated. We compare the seismic and
infrasound data with FMCW radars and the GEODAR radar. FMCW radars are installed at three
locations and provide high frequency measurements of the internal profile of the avalanche as it flows
over the sensor revealing erosion, deposition and the flow regime. The GEODAR radar is a phased
array system located at the bunker on the counter slope. It can track the avalanche over the whole
slope with high resolution, and gives information on avalanche position, velocity and size. The
infrasound sensor is also located at the bunker and the three seismic sensors are spaced along the
slope.
We correlate the magnitude of the avalanche dilute layer and its front velocity with the intensity of the
infrasound signal. Furthermore, we compare avalanche length, height and flow regimes with the
amplitude, duration and frequency content of the seismic signal. This comparison allows the
calculation of seismic and infrasound parameters (length of the signals, amplitude and energy) that
can be useful to characterize type, size and path of snow avalanches. Moreover, we discuss the
feasibility of deducing the avalanche location from the seismic and infrasound data by comparison with
GEODAR data.
Page | 185
1040
Measuring the thermal balance of a snow avalanche
1,2
1
1
1,2
Walter Steinkogler , Betty Sovilla , Tobias Jonas , Michael Lehning
1
2
SLF, Davos Dorf, Switzerland, CRYOS, EPFL, Lausanne, Switzerland
Avalanches can exhibit many different flow regimes from powder clouds to slush flows. Flow regimes
are largely controlled by the properties of the snow released and entrained along the path. Recent
investigations showed the temperature of the moving snow to be one of the most important factors
controlling the granulometry and thus the mobility of the flow. The temperature of an avalanche is
mainly determined by the temperature of the released and entrained snow but also increases by
frictional and collisional processes with time.
The aim of this study is to calculate the thermal balance of an avalanche using infrared thermography
technology. For this work an avalanche was artificially released at the Flüelapass (2383 m.a.s.l.) close
to Davos, Switzerland. A thermal imaging camera was used to assess the temperature before, during
and just after the avalanche with a high spatial resolution. Snow profiles along the avalanche track and
terrestrial laser scans, conducted before and after the avalanche, allowed to quantify the temperature
of the eroded snow layers. This data set allows for the first time to calculate an entire thermal balance,
from release to deposition, of an avalanche. The comparison between the measured temperature of
the entrained snow layers and the temperature of the deposition allowed to draw conclusions whether
the main contribution to the warming of the snow in the avalanche arose from friction or entrainment of
relatively warmer snow.
Our results allow for a more comprehensive understanding of snow temperatures in avalanche flow
and their consequence on flow regimes. This information can directly be used to enhance the
performance of avalanche dynamics models and are thus of great interest for practitioners. We further
discuss advantages and limitations of the presented method and the technologies.
Page | 186
856
Self-consistent approximations to the dynamics of basal entrainment in snow
avalanches
1
2
Dieter Issler , Tómas Jóhannesson
1
2
Natural Hazards Division, Norwegian Geotechnical Institute, Oslo, Norway, Icelandic Meteorological
Office, Reykjavík, Iceland
Observations indicate that the highest erosion rates in snow avalanches usually occur at the very front
of the flow. However, despite lower erosion rates, basal entrainment may give a similar contribution to
the mass balance due to the extended area over which it occurs. For physical reasons, the erosion
rate must be determined uniquely by the properties of the snow-cover and the dynamic characteristics
of the flow. In contrast, entrainment models typically contain adjustable parameters whose relation to
the snow-cover and flow characteristics remains elusive.
In order to shed some light on this question, a quasi-stationary eroding flow over a perfectly brittle bed
was studied in the infinite-slope approximation. The brittleness assumption implies that the shear
stress must exceed a critical value, but no work is expended to break the interparticle bonds. A key
point is that the dynamics keeps the bed shear stress locked at the critical shear stress value as long
as erosion takes place. For a Bingham visco-plastic flow rheology, analytical solutions for the velocity
profile can be found and the entrainment rate uniquely determined from a transcendental equation,
without adjustable parameters beyond the measurable material properties. For more complicated
rheologies, unique solutions can be found numerically.
The approximation of an infinitely long, quasi-stationary flow can be removed at the expense of
analytical solvability by implementing the model in an Eulerian quasi-3D flow code. The nonequilibrium erosion rate is approximated by the equilibrium erosion rate at a different slope angle that
gives the same depth-averaged flow velocity. As an alternative to the computationally expensive
solution of a transcendental equation for every grid point and time step, the use of the velocity profile
of a corresponding non-entraining flow has also been studied. Selected simulations serve to illustrate
the behavior of the model.
Page | 187
953
Development, refinement and application of a new evaluation and comparison
method for computational snow avalanche simulation
1
1
2
3
3
Jan-Thomas Fischer , Reinhard Fromm , Peter Gauer , Betty Sovilla , Walter Steinkogler , Matthias
4
3
Granig , Marc Christen
1
Institute of Natural Hazards, Austrian Research Centre for Forests, BFW, Innsbruck, Austria,
2
3
Norwegian Geotechnical Institute - NGI, Oslo, Norway, WSL Institute for Snow and Avalanche
4
Research SLF, Davos, Switzerland, Austrian Service for Torrent and Avalanche Control - Centre for
Snow and Avalanches, Schwaz, Austria
This contribution summarizes the results and further developments of the Automated Indicator based
Model Evaluation and Comparison (AIMEC). Computational snow avalanche simulation has gained
importance in hazard mapping and mitigation planning. The simulations are based on depth averaged
models operating in three-dimensional terrain, providing results such as flow velocity, depth and
pressure. Complexity and large amount of results make an objective comparison of a high number of
simulation runs challenging and difficult to interpret. Here we present applications of AIMEC, which
has been introduced to: (1) effectively handle large amounts of simulation results, (2) provide
mathematical definitions representing main avalanche features in a clear and comprehensive way, (3)
provide the basis to evaluate deterministic simulation results by means of probabilistic methods. Key
point of this method is a coordinate transformation in an avalanche path dependent system, which
allows to introduce new metrics, the so called indicators. The indicators allow to directly analyze large
samples of simulation runs with respect to e.g., the avalanche run out or destructiveness. Two
examples show how to (1) improve model calibration by evaluating simulation results with field data
and (2) compare the results of different simulation software, highlighting the influence of the different
model implementations. The new method is helpful for the interpretation of avalanche simulations with
a broad applicability in model evaluation, comparison as well as model calibration.
Page | 188
A6.3b - Ice melt in Antarctica and Greenland and its implication for ice sheet
and ice shelf stability in the 21st century
09.07.2013 10:15-11:45, Forum
221
Ice-sheet and mountain glacier mass balance estimates
1
1
1
1
1
2
3
Jianbin Duan , C.K. Shum , Junyi Guo , Ian Howat , Zhenwei Huang , Xiaoli Su , Hyongki Lee ,
4
5
6
7
Alexander Braun , Graham Cogley , Xiaoli Ding , Chungyen Kuo
1
2
School of Earth Sciences, Ohio State University, Columbus, United States, Ohio State University,
3
Columbus, United States, Department of Civil and Environmental Engineering, University of Houston,
4
Houston, United States, Department of Geosciences, University of Texas at Dallas, Dallas, United
5
6
States, Department of Geography, Trent University, Peterborough, Canada, Department of Land
7
Survey & Geo-informatics, Hongkong Polytechnic University, Hongkong, China, Department of
Geomatics, National Cheng Kung University, Tainan, Taiwan, Republic of China
Pre-IPCC AR5 assessment studies seem to indicate an arguably reasonably closed sea-level budget
near to the observed sea-level rise of ~3 mm/yr, with about 22% signal unexplained (~0.7 mm/yr is the
difference between the observed and explained sea-level signals), e.g., [Church et al., 2011]. This
sea-level budget discrepancy is primarily attributed to the wide range of estimates of sea-level
contributions from rapidly ablating mountain glaciers and ice-sheets. Observations from the Gravity
Recovery and Climate Experiment (GRACE) spaceborne gravimetry are capable of measuring the
total mass changes of ice sheets. Recently, estimates of mountain glacier mass balance became
possible by using GRACE monthly solutions with corrections of hydrological and other signals.
However, large discrepancies exist because of post-processing techniques applied and large
uncertainties from model outputs used for corrections such as atmospheric pressure, hydrology, and
glacial isostatic adjustment (GIA). The fidelity of GIA models, in particular over Antarctica, and
notwithstanding recent improvements from new ice-sheet GIA models together with 'reconciled' ice
sheet mass balance estimates, could still contribute non-negligible errors. At present contemporary
mountain glacier mass balance estimates remain controversial, including the Asian High Mountain
(AHM) glacier systems. Herein, we present preliminary results to quantify Antarctic and Greenland ice
sheet mass balance and mountain glaciers including the AHM glaciers primarily using satellite
geodetic measurements from GRACE satellite gravimetry and satellite altimetry including rigorous
uncertainty estimates.
Page | 189
621
Effects of changes in the physics description of RACMO2 on the modeled
climate (1979-2010) of Antarctica
1
1
1
1
Melchior van Wessem , Jan Lenaerts , Carleen Reijmer , Michiel van den Broeke , Willem Jan van de
1
2
Berg , Erik van Meijgaard
1
2
IMAU, Utrecht University, Utrecht, Netherlands, Royal Netherlands Meteorological Institute (KNMI),
De Bilt, Netherlands
In recent years the regional atmospheric climate model RACMO2 has been used and adapted for
climate and mass balance studies over polar regions such as Greenland and Antarctica. The physics
package of RACMO2 has been upgraded from RACMO2.1 to RACMO2.3, constituting amongst others
an inclusion of a parameterization for ice super-saturation, changes in the turbulent and radiative flux
schemes and changes in the cloud convection and prognostic schemes. We present the effects of
these changes on the modeled surface mass balance of Antarctica and related key parameters such
as the surface energy budget components. RACMO2.3 gives a better representation for East
Antarctica based on a comparison of modeldata with observations. The inclusion of the new supersaturation parameterization has contributed to more and optically thicker clouds to be transported onto
the continent. This has led to increased precipitation rates and an increased downward longwave
radiative flux. The latter has reduced the surface temperature bias, based on a comparison with 10 m
snow temperatures from ice cores over the whole continent, and consequently reduced the bias in the
sensible heat flux. Similar changes are seen for West Antarctica and the Antarctic Peninsula but an
assessment of these changes is hampered by a lack of observational data.
Page | 190
359
Evolution of the surface mass balance of the Greenland ice sheet from 19602012
1
1
Jan van Angelen , Michiel van den Broeke
1
IMAU, Utrecht University, Utrecht, Netherlands
We assess the surface mass balance (SMB) of the Greenland ice sheet (GrIS), its individual
components and recent trends. We use output of a high-resolution (11 km) regional atmospheric
climate model (RACMO2), automatic weather stations and GRACE data. Persistent changes in upper
st
air circulation patterns in the 21 century results in advection of relatively warm continental air towards
the GrIS, on top of the enhanced radiative forcing by increased CO2 levels. This results in an increase
of T2m, of more than 2 K over 2007-2012 compared to 1960-90, accompanied by decreased albedo
and an extra absorption of shortwave radiation by 9% in the summer months (JJA).
From 1990 onwards, we see a gradual decrease of the SMB, accelerating after 2005, with record low
years in 2007, 2010 and 2012. Up to 2005 the increased surface runoff is partly compensated by
increased accumulation rates. Since then, accumulation rates have decreased, being one of the
reasons of the record low SMB values. Other causes are the loss of the buffering effect of firn pore
space at higher altitudes and decreasing refreezing rates in the higher ablation area. As a result, the
GrIS has lost in total ±2000 Gt of mass from surface processes alone since 1990 and half of that in the
last 6 years. This mass loss simulated by RACMO2 is in very good agreement with the mass balance
retrievals from GRACE.
Page | 191
476
Ice-dynamic projections of the Greenland ice sheet in response to future
atmospheric and oceanic warming
1
1
1
Johannes J. Fürst , Heiko Goelzer , Philippe Huybrechts
1
Earth System Science Group & Departement Geografie, Vrije Universiteit Brussel, Brussels, Belgium
Continuing global warming will have a strong impact on the Greenland ice sheet in the coming
centuries. We use a higher-order ice flow model, initialised to the present-day state, to simulate future
ice mass changes driven by both atmospheric and oceanic temperature changes. The surface mass
balance is calculated with a degree-day runoff/retention model. The projections account for direct
effects on ice dynamics from ocean-induced outlet glacier discharge change and from subglacial
meltwater drainage that lubricates the base. The modelled outlet glacier discharge change is linked to
regional patterns of ocean warming via an observationally calibrated relation.
The mass evolution is projected up to 2300 AD for a suite of ten Atmosphere Ocean General
Circulation Models and four Representative Concentration Pathway scenarios. In these projections,
surface mass balance and dynamic ice discharge are mutually competitive in removing mass from the
ice sheet. Increasing runoff reduces the ice volume that reaches the marine margin and thereby
decreases ice calving rates. Discharge is also limited by a gradual loss of the ocean contact and a
retreat of the ice sheet margin on land. We find Greenland contributions to global sea-level rise
between 1.4 and 16.6 cm by 2100 AD. This mass loss is predominantly caused by changes in surface
mass balance. The results suggest that observed rates of change over the last decade cannot simply
st
be extrapolated over the 21 century on account of a different balance of processes causing mass loss
over time. They also indicate that the largest source of uncertainty arises from the surface mass
balance and the underlying climate change projections, and not from ice dynamics.
Page | 192
1002
Summer 2012 surface melting at NEEM ice core drilling site in Northwest
Greenland
1
1
1
1
1
2
Paul Vallelonga , H.A. Kjær , R Gjermundbo , D. Dahl-Jensen , H.C. Steen-Larsen , M. Hirabayashi ,
3
A Borundra
1
2
Centre for Ice and Climate, Copenhagen, Denmark, National Institute of Polar Research, Tokyo,
3
Japan, Lamont-Doherty Earth Observatory, Columbia University, New York, United States
The warm atmospheric temperatures over Greenland for the period 12-15 July resulted in substantial
warming of surface snow and subsequent formation of ice lenses and density variations as observed
from a sequence of snowpit measurements at NEEM site (Northwest Greenland, N77˚26'W51˚04').
The warming event altered snow temperatures to 1.6 m depth, and warmed the upper 0.8 m of
snowpack to melting temperature. Formation of ice layers and percolation of water into the snowpack
was observed to 1.4 m depth. The surface snowpack cooled again within a few days of the return to
cooler surface temperatures after July 15. We present observations of surface snow temperatures,
impurity data and water stable isotope ratios sampled before, during and after the melt event.
Page | 193
1279
Investigating potential for Jakobshavn catchment expansion due to marginal
drainage from saturated crevasses
1
2
Derrick J Lampkin , Byron R. Parizek
1
University of Colorado, Institute of Arctic and Alpine Research, Boulder, CO, United States,
2
Mathematics and Geosciences, Pennsylvania State University, DuBois, PA, United States
Recent estimates show that Greenland's contribution to sea level more than doubled in the past
decade. Coincident with the changes in flow dynamics on Jakobshavn is an increase in surface melt
accompanied by the proliferation of surface lakes which rapidly drain due to hydrofracture or through
moulins along the margins of the Greenland Ice Sheet. Though the importance of supraglacial lake
hydraulics and its impact on ice sheet mass balance is a subject of contemporary investigations, much
of the focus has been on larger lakes outside the main trunk of Jakobshavn. We have recently
documented surface melt water infiltration due to drainage from water-filled crevasses 'saturated
crevasses' within the shear margins of Jakobshavn Isbræ. Estimates on potential drainage volume
-3
3
-8
3
-2
3
from the largest crevasse system are ~9.23 x 10 km ± 2.15 x 10 km and ~ 4.92 x 10 km ± 3.58 x
-8
3
10 km respectively over a 16-day interval. This work seeks to understand the long-term impact of
drainage from saturated crevasses through the application of numerical ice sheet modeling to evaluate
impact on basin-scale ice mass flux into Jakobshavn Isbræ.
Page | 194
C2.3c - Clouds, aerosols and precipitation at high latitudes
09.07.2013 10:15-11:45, Studio
1201
Unmeasured solid precipitation over the Arctic regions
1
2
Ismail Gultepe , Andrew J. Heymsfield
1
2
Cloud Physics and Severe Weather Research Section, Environment Canada, Toronto, Canada, P.O.
Box 3000, NCAR, Boulder, United States
Solid precipitation measurements at cold temperatures (< -10°C) are strongly related to the
measurement sensor type, particle shape (habit), size, precipitation rate (PR), and cloud dynamical
conditions. Most of the precipitation sensors are not calibrated for cold temperatures e.g. < -20°C and
-1
they cannot measure PR< 0.5 mm hr . In this presentation, three unmeasured precipitation types: ice
fog (IF), light snow (LSN), and frost (FR), will be discussed in detail. The measurements from the Fog
Remote Sensing And Modeling-Ice Fog (FRAM-IF) project, at Yellowknife International Airport, NWT,
Canada, during the winter of 2010-2011, are used for this study. Ice fog forms at the cold
temperatures (i.e. < -10°C) in ice saturated conditions. Its precipitation rate is usually less than 0.2 mm
-1
-1
hr . Light snow measurements in this work are defined as < 0.5 mm hr . Frost cannot be measured
with regular precipitation sensors and its amount has not been included in previous precipitation
analysis. The results suggest that the occurrence of IF, LSN, and FR over 67 days was about 14%,
23%, and 12%, with durations at least 1 hr, respectively. In this work, unmeasured precipitation types
and neglecting them in precipitation studies and measurement will be presented and its impact on the
Arctic heat and moisture budget calculations will be emphasized.
Page | 195
492
Simulating Arctic mixed-phase clouds with aerosol-dependent ice nucleation
and ice nuclei depletion
1
1
Marco Paukert , Corinna Hoose
1
Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
Arctic stratus clouds frequently consist of long-lived supercooled liquid layers which precipitate ice. In
semi-idealized simulations with a cloud-resolving model, we investigate for which concentrations of ice
nucleating aerosols (here: mineral dust and ice-active bacteria) a stratiform supercooled liquid cloud
remains stable, i.e. maintains an approximately constant liquid water path and ice water path over
several hours. For this purpose, the ice nucleation scheme in the COSMO model has been replaced
by an ice nucleation active site density approach for immersion freezing, relating the ice nuclei number
to the temperature and to the aerosol surface area based on results from laboratory experiments. In
addition, depletion of ice nuclei is taken into account, assuring that only entrainment of fresh aerosol
particles or further cooling of an air parcel leads to the formation of ice crystals. The model is applied
to the simulation of a cloud which was observed during the ISDAC campaign. The evolution of the
liquid/ice partitioning in the cloud is highly sensitive to both the vertical velocity distribution, the ice
crystal growth parameterization and the ice nuclei concentration. It is found that both dust and bacteria
concentrations need to be several orders of magnitude higher than our initial assumptions based on
typical background values to reach the transition from the growing to the glaciating state through
immersion freezing.
Page | 196
694
Heterogeneous formation of polar stratospheric clouds - nucleation of nitric
acid trihydrate (NAT) in the Arctic stratosphere
1
2
2
3
4
5
Christopher Hoyle , Ines Engel , Beiping Luo , Michael C. Pitts , Lamont R. Poole , Jens-Uwe Grooß ,
2
Thomas Peter
1
2
Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, Villigen, Switzerland, Institute for
3
Atmospheric and Climate Science, ETH, Zurich, Switzerland, NASA Langley Research Center,
4
Hampton, United States, Science Systems and Applications Incorporated, Hampton, United States,
5
Institut fur Energie- und Klimaforschung - Stratosphare (IEK-7), Forschungszentrum Julich, Julich,
Germany
Satellite based observations during the Arctic winter of 2009/2010 provide firm evidence that, in
contrast to the current theory, the nucleation of nitric acid trihydrate (NAT) in the polar stratosphere
does not only occur on preexisting ice particles. In order to explain the NAT clouds observed over the
Arctic in mid December 2009, a heterogeneous nucleation mechanism is required, occurring on the
surface of dust or meteoritic particles. For the first time, a detailed microphysical modelling of this NAT
formation pathway has been carried out. Heterogeneous NAT formation was calculated along tens of
thousands of trajectories, ending at Cloud Aerosol Lidar with Orthogonal Polarisation (CALIOP)
observation points. Comparing the optical properties of the modelled NAT PSCs with these
observations enables the thorough validation of a newly developed NAT nucleation parameterisation,
which has been built into the Zurich Optical and Microphysical box Model (ZOMM). The
parameterisation is based on active site theory, is simple to implement in models and provides
substantial advantages over previous approaches which involved a constant rate of NAT nucleation in
a given volume of air. It is shown that the new method is capable of reproducing observed PSCs very
well, despite the varied conditions experienced by air parcels travelling along the different trajectories.
Page | 197
764
Polar stratospheric clouds over Finland in the 2012/2013 Arctic winter
measured by two Raman LiDARs
1
1
1
2
3,4
5
Mika Komppula , Anne Hoffmann , Eleni Giannakaki , Rigel Kivi , Otto Schrems , Immler Franz
1
2
Kuopio Unit, Finnish Meteorological Institute, Kuopio, Finland, Arctic Research Centre, Finnish
3
Meteorological Institute, Sodankylä, Finland, Department of Chemistry, University of Bremen,
4
Bremen, Germany, Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany,
5
DG Research and Innovation, European Commission, Brussels, Belgium
Already in December 2012, the Arctic stratospheric vortex reached temperatures sufficiently low for
polar stratospheric cloud (PSC) formation over wide areas of Northern Europe and whole Finland.
Within Finland, stratospheric aerosol lidar measurements have been and are performed with two
Raman lidar systems, the PollyXT, owned by the Finnish Meteorological Institute (FMI) and situated
well below the Arctic circle close to Kuopio (63 N, 27 E) and the MARL lidar owned by the AlfredWegener-Institute for Polar and Marine Research (AWI), and situated at the FMI Arctic Research
Centre in Sodankylä (67 N, 26 E). The PollyXT has been designed as an autonomous tropospheric
lidar system, but it has proven to be able to detect aerosol backscatter and depolarization at least as
high up as 25 km.
Measurements are ongoing as far as low clouds allow for stratospheric analysis with both lidars until
the end of PSC season in February. For the winter 2012/2013, PSC occurrence frequency, types and
characteristics will be determined. Comparative analysis with Calipso lidar profiles covering Finland
will be performed.
Preliminary results from December 17-24 show PSCs detected in Kuopio during seven days with the
PollyXT lidar. The altitude of the clouds varied in the range of 17-25 km. In Sodankylä the
measurements were running on one day during the same period and PSCs were observed between
altitudes 17-25 km. For the same time period (December 17-24, 2012) CALIPSO has observed
stratospheric layers at all overpasses over Finland (9 tracks on five days). The clouds were observed
between 18.5 and 26 km, with varying geometric and optical thickness.
Page | 198
870
Polar stratospheric clouds detection in the Arctic environment with the opacity
sensor ODS
1
1
2
2
Daniel Toledo , Pascal Rannou , Jean-Pierre Pommereau , Alain Sarkissian , Thomas Foujols
1
2
GSMA, Université de Reims Champagne Ardenne, Reims, France, LATMOS, Université de
Versailles-St-Quentin, Guyancourt, France
2
Polar stratospheric clouds (PSC) are regarded as determinant elements for the ozone depletion
processes occurring at high latitudes during winter and spring, providing the surfaces required for a
number of heterogeneous catalytic reactions. In the frame of the IAOOS (Ice Atmosphere Arctic
Ocean Observing System) project, a flotilla of small stations equipped with several instruments will be
send in the arctic ice sheet during the winter to monitor the upper ocean, the lower atmosphere and
the Arctic sea-ice. The small and advanced optical depth sensor ODS, designed to probe the aerosol
and the cloud layer will be included in the payload.
ODS measurements will allow to determine the role of the aerosols and the clouds in the atmospheric
radiation budget. The method used in this work to detect PSC consists in analyzing the color ratio of
scattered light at the sunset and the sunrise to retrieve the opacity and the altitude of the clouds.
In this presentation, we will present the principle of the instrument and we will describe the retrieval
procedure. To test our procedure, we will show the retrieval made from SAOZ observations which is
performing measurements in a similar environment.
Page | 199
387
Tethered balloon observations of supercooled drops at -32 C in stratus clouds
at the South Pole
1
1
Qixu Mo , Paul Lawson
1
SPEC inc, Boulder, United States
The presence of water drops at -32°C is not expected and is generally not included in Polar models of
radiative transfer. In January 2009 SPEC deployed its tethered balloon system (TBS) with a
microphysical instrument package in stratus clouds at South Pole Station (SPS). The instrument
package contained a cloud particle imager (CPI) with 3-micron pixel resolution that was capable of
distinguishing images of cloud drops from (non-spherical) ice particles. The TBS measurements were
made in conjunction with a Micro Pulse Lidar (MPL) owned NASA and operated by NOAA, with
support from the NSF. The in situ TBS measurements were found to correlate very strongly with
exceptionally strong backscatter return from the SPS MPL, which was vertically pointing and located
about 300 m from the TBS launch site. The strong correlation between extreme MPL backscatter and
corresponding in situ measurements of supercooled cloud drops was unique, and was not observed in
any clouds without liquid water. The liquid water layer was found between - 30 and -32 C, with ice
cloud above and below. Examination of other days when the TBS was not operating also showed the
MPL signature of the supercooled liquid layer in -28 to -32 C region. The frequency of occurrence in
summer months, when stratus cloud was present in 2009, was about 25%. When MPL data were
examined for winter months at SPS the supercooled water signature was even seen on some days
when the surface temperature was - 70 C; a sharp inversion facilitated the supercooled liquid layer at
around -32 C. A two-stream radiative transfer model shows that radiative forcing effects of the
supercooled water cloud at SPS is significant during both the austral summer and winter.
Page | 200
B3.1a - General dynamics
09.07.2013 10:15-11:45, Wisshorn
345
Tropospheric Rossby wave breaking and its response to climate change
1,2
3
2
Elizabeth Barnes , Dennis Hartmann , Lorenzo Polvani
1
Department of Atmospheric Science, Colorado State University, Fort Collins, United States,
2
Department of Ocean and Climate Physics, Lamont-Doherty Earth Observatory, Columbia University,
3
Palisades, United States, Department of Atmospheric Science, University of Washington, Seattle,
United States
We identify Rossby wave breaking in reanalyses and in GCMs from the CMIP3 and CMIP5 data sets
using an algorithm that searches for overturning of absolute vorticity contours on pressure surfaces.
We demonstrate that a poleward shift of the North Atlantic and Southern Hemisphere jets with climate
change is accompanied by a decrease in poleward (cyclonic) wave breaking. While anticyclonic wave
breaking shifts poleward with the jet, cyclonic wave breaking shifts less than half as much and reaches
a poleward limit near 60 degrees latitude. In the North Atlantic, the decrease in high-latitude wave
breaking in the 21st Century CMIP5 simulations is consistent with the decrease in blocking anticyclone
frequency there. Comparisons of the observed distributions of wave breaking with those from the
GCMs suggests that wave breaking on the poleward jet flank may have already reached its poleward
limit and will likely become less frequent if the jet migrates any further poleward.
Page | 201
710
Storm track response to climate change: insights from simulations using an
idealized dry GCM
1
2
Cheikh Mbengue , Tapio Schneider
1
2
California Institute of Technology, Pasadena, United States, ETH Zürich, Zürich, Switzerland
The competing mechanisms present in the comprehensive climate models often used to study storm
track dynamics make it difficult to determine the primary mechanisms responsible for storm track
migration. We are thus prompted to study storm track dynamics from a simplified and idealized
framework, which enables the decoupling of mean temperature effects from the effects of static
stability and of tropical from extratropical effects. Using a statistically zonally symmetric, dry general
circulation model (GCM), we conduct a series of numerical simulations to help understand the storm
track response to global mean temperatures and to the tropical convective static stability, which we
can vary independently.
These simulations provide several insights, which enable us to extend upon existing theories on the
mechanisms driving the poleward migration of the storm tracks. We demonstrate a poleward migration
of the midlatitude storm tracks in dry atmospheres with fixed pole-equator temperature contrast and
increasing radiative equilibrium mean temperature, without changes in convective static stability. In the
simulations where we independently vary tropical convective static stability, we find a marked
poleward migration of the storm tracks. However, our decomposition shows that meridional
temperature gradients, and not static stability, determine the location and the intensity of the storm
tracks. This suggests that although the storm tracks are sensitive to tropical convective static stability,
it influences them indirectly. Furthermore, our simulations show that the storm tracks generally migrate
in tandem with the terminus of the Hadley cell. Therefore, we hypothesize that it is possible that the
Hadley cell provides the tropical-extratropical communication necessary to generate the storm track
response to tropical convective static stability we observe in the simulations. The results contained
herein could be used to supplement ongoing storm track research in moist atmospheres using
comparatively more comprehensive GCMs to understand storm track dynamics in earth-like
environments.
Page | 202
664
Deformation: a new diagnostic for the evolution of large-scale flow
1
1
Clemens Spensberger , Thomas Spengler
1
Bjerknes Centre for Climate Research, University of Bergen, Bergen, Norway
Deformation plays a key role in atmospheric dynamics, because it provides a dynamical measure of
the interaction between different scales. By transforming a square parcel of air into an increasingly
elongated rectangle, deformation gradually increases pertinent length scales along the axis of
dilatation while simultaneously reducing those scales perpendicular to the axis. From a climatology of
deformation, here constructed from ERA-Interim reanalysis data 1979—2011, we show that four
processes are associated with deformation: (1) frontogenesis acting mostly at lower levels, (2) the
movement and evolution of jet streams in the upper part of the troposphere, (3) orographic blocking,
which is most pronounced around the height of the mountain top and (4) Rossby wave breaking
associated with atmospheric blocks. As a consequence of the properties of deformation, these four
processes link the synoptic scale with the mesoscale.
This study is a step towards a systematic assessment of the role of deformation in large-scale
atmospheric dynamics. For each of the processes we present a typical example from the dataset as
well as a composite analysis and contrast those observational results with analytical solutions for
idealized setups. Our results show, that for each of the four processes named above, deformation
adds a valuable new perspective, helping to better understand those processes. E.g, for orographic
blocking, deformation provides local information about the strength of the block without relying on
mean characteristics of the impinging flow field. Furthermore, the deformation perspective confirms
previous findings suggesting a dynamic link between Rossby wave breaking and atmospheric blocks.
Based on the climatology of deformation, we propose a dynamical interpretation of the NAO as a
variation between a one-jet and a two-jet regime in the North-Atlantic and of the PNA as a variation in
the length of the North-Pacific storm track.
Page | 203
451
A simple GCM model study on the relationship between ENSO and the
Southern Annular Mode
1
2
3
Tingting Gong , Steven Feldstein , Dehai Luo
1
2
Institute of Oceanography, Chinese Academy of Sciences, Qingdao, China, Department of
3
Meteorology, The Pennsylvania State University, State College, United States, RCE-TEA, Institute of
Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
This study investigates the relationship between (El Niño/Southern Oscillation) ENSO and Southern
Annular Mode (SAM) events with an idealized general circulation model. A series of model
calculations are performed to examine why positive (negative) intraseasonal SAM events are
observed to occur much more frequently during La Niña (El Niño). Seven different model runs are
performed; a control run, three El Niño runs (the first with a zonally-symmetric heating field, the
second with a zonally-asymmetric heating/cooling field, and the third that combines both fields), and
three La Niña runs (with heating fields of opposite sign).
The model runs with the zonally-symmetric and combined heating fields are found to yield the same
relationship between the phase of ENSO and the preferred phase for SAM events as is observed in
the atmosphere. In contrast, the zonally-asymmetric model runs are found to have the opposite
SAM/ENSO phase preference characteristics. Since a reduced midlatitude meridional potential
vorticity gradient has been linked to a greater frequency of positive phase SAM events, and vice versa
for negative SAM events, the meridional potential vorticity gradient in the various model runs was
compared. The results suggest that the phase preference of SAM events during ENSO arises from the
impact of the zonal mean heating on the midlatitude meridional potential vorticity gradient.
Page | 204
1129
The connection between tropical convection and heatwaves in Southeastern
Australia
1,2
1
1,2
Tess Parker , Gareth Berry , Michael Reeder
1
Monash Weather and Climate, School of Mathematical Sciences, Monash University, Clayton,
2
Australia, Centre of Excellence for Climate Systems Science, Monash University, Clayton, Australia
Heatwaves in summer over Southeastern Australia are invariably associated with strong slow-moving
transient anticyclones, which direct warm dry air from the interior in a northerly or northwesterly flow
over this region. These events are associated with propagating Rossby waves, which grow in
amplitude and eventually overturn. The dynamical link between heatwaves in this region and tropical
cyclones or strong tropical convection is investigated using ERA-Interim reanalysis and IBTRaCS
named storm data. It is shown that the anticylonic PV anomaly which is generated over the
southeastern regions as a result of Rossby wave breaking is intensified or maintained by the injection
of low-PV air which is generated by strong convective heating at lower latitudes. The simulation of
these events by GCMs is also examined using the ACCESS model.
Page | 205
A3.2a - Ocean’s role in climate variability, change, and predictability
09.07.2013 10:15-11:45, Schwarzhorn
129
Significant contribution of multidecadal ocean variability in recent warming of
the Northern continents
1
Sumant Nigam
1
Atmospheric & Oceanic Science, University of Maryland, College Park, United States
Surface air temperature (SAT) over the Northern continents has risen sharply in recent decades. The
1970-onward linear warming trend over the Pacific Northwest, western-central Canadian provinces,
and the Great Plains is ~3 times the corresponding century-long trend. Are the substantially larger
recent trends indicative of accelerated secular change, multidecadal natural variability, or both?
That both secular change and multidecadal natural variability are manifest in the 20th century SAT
record is clear as it is not one of monotonic rise but marked by multidecadal fluctuations. Both the
origin of fluctuations and related aliasing of the linear SAT trend over multidecadal periods are of
interest in attribution of the recent sharp rise in temperature. Climate model based estimates abound
but exhibit substantial spread in warming scenarios due to varied treatment of convection, clouds, and
aerosols.
An alternate strategy - analysis of the observational record itself - is pursued here as it provides direct
assessment of the response of the real climate system with its myriad feedbacks (not all represented
in climate models) to anthropogenic influences. This assessment has its own caveats stemming from
analysis of just one realization of climate evolution.
The secular warming of the continents is estimated factoring for multidecadal natural variability which
is characterized from two SST datasets to bracket the diagnosis. SAT reconstruction shows one-third
of the recent (1970-2009) winter SAT trend, averaged over Northern continents, linked with SST
natural variability which dominates trends over central-eastern North America, Greenland, and
northern Eurasia. Atlantic Multidecadal Variability (AMV) is a significant contributor, in part, from
anomalous thermal advection. Its contribution to North American—Greenland SAT trends is
impressive (one-third), indicating prospects of some reprieve in the AMV flip-phase. Factoring for
multidecadal natural variability yields reduced estimates for the post-1970 secular warming but these
remain larger than their full-century counterparts.
Page | 206
322
The accelerated warming and hiatus decades in the CMIP5 models
1,2
1
Yi Song , Yongqiang Yu
1
State Key Laboratory of Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of
2
Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), Beijing, China, College of Earth
Science, University of Chinese Academy of Sciences, Beijing, China
Besides the long-term warming trend, the observed global mean surface air temperature (TAS) also
th
exhibits accelerated warming or hiatus phenomena in some decades of the 20 century. We first
evaluate the ability of coupled models from Coupled Model Intercomparison Project Phase 5 (CMIP5)
achieve to reproduce accelerated warming and hiatus phenomena, and then explore their detailed
physical mechanisms in this study. By analyzing 20 CMIP5 models, we find that global averaged TAS
th
show a decadal variation under long-term warming trend during the 20 century. The global energy
budget analysis from all coupled models indicates that the decadal trend in TAS places a relatively
weak constraint on the 10-yr mean net top-of-atmosphere (TOA) radiation, but the net TOA radiation
has a very close relationship with full-depth OHC. This implies the TAS changes may associate with
ocean re-distribution of heat. Composited OHC trends for hiatus decades show a significant decrease
of SST and upper OHC and increase of heat penetrated into the subsurface or deep ocean, while the
trends for accelerated warming decades show a reversed change. Based on multi-model ensemble
average, the results show the Pacific subtropical cells (STC) experience a significant strengthen
(slowdown) in both hemispheres for hiatus (accelerated warming) decades as a respond to the
strengthening (weakening) trade winds over the tropical Pacific. Both surface heating and ocean
dynamics contribute to the SST changes in Indian Ocean, and the Indonesian Throughflow (ITF) has a
great impact on the changes of subsurface sea temperature in South Indian Ocean. The decadal
variability of Atlantic Meridional Overturning Current (AMOC) and Antarctic Bottom Water (AABW) may
affect deep-ocean temperature, but with great uncertainties. In addition, we suggest external forcing
factors, such as volcanic aerosols and increased GHGs, may lead to a shift of Interdecadal Pacific
Oscillation (IPO) phase.
Page | 207
739
Regional patterns of ocean warming: an important source of uncertainty in
future projections of precipitation and atmospheric circulation
1
2
Shang-Ping Xie , Jian Ma
1
2
University of California San Diego, La Jolla, United States, University of California at Irvine, Irvine,
United States
Precipitation change in response to global warming has profound impacts on environment for life but is
highly uncertain. Effects of sea surface temperature (SST) warming on the response of rainfall and
atmospheric overturning circulation are investigated using Coupled Model Intercomparison Project
simulations. The SST warming is decomposed into a spatially uniform SST increase (SUSI) and
deviations from it. The SST pattern effect is found important in explaining both the multi-model
ensemble mean distribution and inter-model variability of rainfall change over tropical oceans. In
ensemble mean, the annual rainfall change follows a “warmer-get-wetter” pattern, increasing where
the SST warming exceeds the tropical mean, and vice versa. Two SST patterns stand out both in the
ensemble mean and inter-model variability: an equatorial peak anchoring a local precipitation
increase, and a meridional dipole mode with increased rainfall and weakened trade winds over the
warmer hemisphere. These two modes of inter-model variability in SST account for one third of intermodel spread in rainfall projection.
The SST patterns can explain up to four fifth of the inter-model variability in intensity changes of
overturning circulations. SUSI causes both the Hadley and Walker circulation to slow down as
articulated by previous studies. The weakening of the Walker circulation is robust across models as
the SST pattern effect is weak. The Hadley circulation change, by contrast, is significantly affected by
SST warming patterns. As a result, near and south of the equator, the Hadley circulation strength
change is weak in the multi-model ensemble mean and subject to large inter-model variability due to
the differences in SST warming patterns.
Page | 208
700
Unifying role of oceanic warming pattern and climatological rainfall on tropical
rainfall change under global warming
1
2,3
4
4
4
Ping Huang , Shang-Ping Xie , Kaiming Hu , Gang Huang , Ronghui Huang
1
2
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China, Scripps Institution of
3
Oceanography, University of California at San Diego, La Jolla, United States, Ocean University of
4
China, Qingdao, China, Institue of Atmospheric Physics, Chinese Academy of Sciences, Beijing,
China
Tropical convection is the major driver for variability and change in regional climate around the globe.
In response to global warming, regional precipitation change is to first order spatially variable, and
state-of-the-art model projections suffer large uncertainties in its distribution. Different views exist
regarding tropical rainfall change: one predicts increased rainfall in current rainy regions (wet-getwetter), and the other calls for increased rainfall where the sea surface temperature increase exceeds
tropical mean warming (warmer-get-wetter). Here, we analyze Coupled Model Intercomparison Project
Phase 5 multi-model simulations, and present a unifying view for the rainfall change. The seasonal
and annual mean rainfall both bears the characteristics of both the “wet-get-wetter” and “warmer-getwetter” effects. Given that the precipitation climatology is well observed while the ocean warming
pattern poorly constrained, our results suggest that tropical rainfall projection is more reliable for the
seasonal than annual mean.
Page | 209
409
Possible impact of sea surface warming on the spatial variation of winter
precipitation trends in north Japan
1
1
Tomonori Sato , Shiori Sugimoto
1
Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Japan
The role of sea surface temperature (SST) anomaly in modulating the terrestrial precipitation around
Japan was investigated using a regional atmospheric model. Large amount of snowfall occurs during
the cold season in northern Japan as the westerly winter monsoon carries abundant moisture from the
Japan Sea. In a numerical experiment with a realistic SST, there was a larger interannual variation of
precipitation over the Japan Sea and the Pacific Ocean in winter than that in the experiment with
climatology SST, suggesting that the SST variability enhances the oceanic precipitation variability. A
detailed analysis indicated that the terrestrial precipitation over the Japan Sea side (JSS) region in
northern Japan was highly sensitive to the offshore SST through affecting moisture flux toward Japan.
Since the offshore SST was clearly warmer in the 2000s relative to the 1980s, the effect of the longterm SST variation on the changing terrestrial precipitation trend was examined. The experiment with
realistic SST simulated the observed trend in terrestrial precipitation in the JSS region. In contrast, the
precipitation trend was significantly reduced in the experiment with climatology SST. Therefore, the
long-term SST trend is an important factor affecting the precipitation trend in the region of Japan and
the adjacent oceans where SST has significant trends. Precipitation in the Pacific Ocean side of Japan
indicated a weak increasing trend even without the SST trend. This suggests that the changes in the
characteristics of extra-tropical cyclones are also an important factor for precipitation trends around
the Kuroshio extension.
Page | 210
756
Long-term modulations in the decadal climate variability over the North Pacific:
observations and a coupled model simulation
1
1
2
3
Hisashi Nakamura , Takafumi Miyasaka , Bunmei Taguchi , Masami Nonaka
1
2
3
RCAST, University of Tokyo, Tokyo, Japan, ESC, JAMSTEC, Yokohama, Japan, RIGC, JAMSTEC,
Yokohama, Japan
Observations for the post-war period suggest that (quasi-) decadal wintertime climate variability over
the North Pacific may have undergone notable modulations. A 20-year segmented EOF analysis of 3year running-mean anomalies of the North Pacific SST reveals that the subarcitic oceanic frontal zone
was the primary center of action of the extratropical decadal SST variability until the 1980s. The SST
variability there exhibits high correlation with the decadal variability of the surface Aleutian Low and a
PNA-like pattern aloft but no significant simultaneous correlation with the tropical SST variability.
Though extracted in the second EOF, however, this extratropical ocean-atmosphere variability has lost
its predominance in the 1990s and 2000s. Instead, the primary center of action has shifted to the
subtropical oceanic frontal zone, where the decadal SST variability that accompanies the variability of
the subtropical anticyclone is strongly anti-correlated with the tropical SST variability that has
enhanced since the 1980s. A 150-year CGCM integration is found to simulate similar long-term
modulations both in the decadal variability over the extratropical North Pacific SST and in the
associated atmospheric variability.
Page | 211
B1.1b - Advanced methods in data assimilation and ensemble forecasting
09.07.2013 10:15-11:45, Seehorn
1102
Pseudo-orbit data assimilation in DART
1
1
Hailiang Du , Leonard A. Smith
1
Centre for the Analysis of Time Series, London School of Economics and Political Science, London,
United Kingdom
Data assimilation for nonlinear models is a challenging task; one which becomes more challenging
when the system that generated the observations is not a member of the available model class.
Weather forecasting models provide perhaps the most important and successful examples of coping
with these challenges. To the extent that traditional approaches to data assimilation address structural
model error at all, few (if any) produce estimates of the model state consistent with our knowledge of
the structural error and of the observational uncertainty. A promising alternative approach is illustrated,
and shown to yield simultaneously both more consistent estimates of model state, and more
reasonable estimates the (state dependent) model error. The Pseudo-orbit Data Assimilation (PDA)
method is presented and a new stopping criteria. It is shown to provide more efficient and more
coherent nowcasts than variational methods, while it systematically outperforms the Ensemble Kalman
Filter in all examples considered to date. Pseudo-orbit Data Assimilation is currently being included
into the suite of methods available in the NCAR Data Assimilation Research Section´s Data
Assimilation Research Testbed (DART). This will allow a fair comparison of PDA with other data
assimilation approaches not only in the context of low-order models like Lorenz 96 where it has been
proven effective, but also in the context of higher order models including atmosphere and ocean
general circulation models.
Page | 212
757
Data assimilation and ensemble forecast toward the cloud resolving NWP
1
1
1
1
1
2
Kazuo Saito , Hiromu Seko , Takuya Kawabata , Masaru Kunii , Seiji Origuchi , Le Duc , Tohru
2
2
Kuroda , Kosuke Itoh
1
2
Forecast Research Department, Meteorological Research Institute, Tsukuba, Japan, Japan Agency
for Marine-Earth Science and Technology, Yokohama, Japan
Accuracy of numerical weather prediction (NWP) has been considerably improved in recent years.
This achievement was attained by implementation of the nonhydrostatic model with sophisticated
physical processes, advanced data assimilation techniques such as nonhydrostatic 4DVAR, and use
of remote sensing data. However, many difficulties remain in precisely predicting small scale severe
weathers (e.g., torrential rains, and tornados). Spatial and temporal scales of these sever phenomena
are generally small, and evolution of these phenomena is sometimes very sensitive to trivial
differences in the initial condition.
Several studies have been conducted at the Meteorological Research Institute (MRI) of JMA, including
development of a cloud-resolving data assimilation system, assimilation of mesoscale remote-sensing
observation data, and development of mesoscale ensemble prediction systems. Computer resource
and observation data are keys to realize full-scale dynamical and probabilistic forecasts of local sever
weathers.
A five-year research project of high performance mesoscale NWP is underway by MRI and the Japan
Agency for Marine-Earth Science and Technology (JAMSTEC) as one of the five research fields of the
Strategic Programs for Innovative Research (SPIRE). Development of a cloud resolving ensemble
analysis and prediction system is underway. The ultimate goal of the project is to demonstrate
feasibility of quantitative probabilistic prediction of sever whether phenomena using the K-computer.
As for observation data, a field campaign as a possible international test-bed for deep convection with
a dense observation network (Tokyo Metropolitan Area Convection Study; TOMACS) is conducted for
summers of 2011-2013.
Page | 213
942
A modified shallow water model for convective-scale data assimilation
1,2
1
Michael Würsch , George C. Craig
1
2
Universität München, Meteorologisches Institut München, München, Germany, Hans-Ertel Zentrum,
Data Assimilation Branch, München, Germany
Assimilation of high-resolution observations of cumulus convection, such as radar reflectivities, is
challenging. Convective clouds evolve quickly and nonlinearity becomes significant on timescales that
are comparable to the intervals at which observations are available. A common example is the socalled late detection problem. Meteorological radars can only detect relatively large precipitation
particles that do not develop until at least a quarter of an hour after the cloud initiates, by which time
the air flow in the cloud has become fully developed. A second challenge is the intermittency of the
convective cloud field. The observable precipitation features often occupy a small fraction of the
domain, and errors in the background forecast tend to take the form of large spatial displacements or
false alarms and missed events. As a result the background error distributions may be highly nonGaussian.
This talk presents an idealised model designed to capture the nonlinearity and non-Gaussianity of
cumulus convection, which may be more suitable for exploring data assimilation algorithms than some
of the simple models traditionally used. As the model is based on the shallow water equations it
contains gravity waves and interactions of neighbouring gridpoints.
It is shown that the model, although based on very simple mathematics, is still able to produce a
realistic convective lifecycle and therefore contains key characteristics of convection.
The model numerics is introduced and demostrated on a standard situation and a situation with a
mountain in the model domain.
We also show results of data assimilation experiments with a LETKF for different situations.
Page | 214
861
Coupled assimilation of both atmospheric and oceanic observations for ENSO
prediction using an intermediate coupled model
1
1
Fei Zheng , Jiang Zhu
1
Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), Beijing, China
The initial surface and subsurface temperature fields are important for El Niño Southern Oscillation
(ENSO) prediction due to the ocean's long memory. As a result, most ENSO predictions are initialized
by ocean data assimilation. However another key for the development of an ENSO event is the wind
anomalies in the western Pacific associated with air-sea coupled tropical convection systems.
Therefore the assimilation of both atmospheric and oceanic observations should be taken into account
for ENSO prediction. However one difficulty is that the atmosphere has relative short memory on its
initial conditions. This can be even worse if one uses the intermediate coupled models in which the
atmospheric components are statistical and slavery to ocean components. In this case, the
atmospheric models do not have any memory on its initial conditions and the adjustment of the
atmospheric state made by assimilation cannot impact on model forecast.
In this study we use the coupled covariance to assimilate both atmospheric and oceanic observations
based on ensemble Kalman filter with an intermediate coupled model. The coupled covariance
enables the assimilation of atmospheric observations to adjust the ocean states and can overcome the
above mentioned difficulty technically. By a series of experiments using both simulated and realistic
observations, we found that the assimilation of atmospheric observations (i.e., wind in this study) can
help to improve the surface and subsurface currents in ocean because the correlation between the
wind and ocean currents is stronger than that between ocean temperature and ocean current in the
equatorial Pacific. Finally we demonstrate that initialized by the coupled assimilation the prediction
lead time with useful skills can reach up to two years.
Page | 215
1208
Development of an ensemble-based data assimilation system with a coupled
atmosphere-ocean GCM
1
1,2
1,3,4
1
1
Nobumasa Komori , Takeshi Enomoto , Takemasa Miyoshi , Bunmei Taguchi , Akira Yamazaki
1
2
Earth Simulator Center, JAMSTEC, Yokohama, Japan, Disaster Prevention Research Institute,
3
Kyoto University, Uji, Kyoto, Japan, RIKEN Advanced Institute for Computational Science, Kobe,
4
Japan, University of Maryland, College Park, United States
In order to overcome the problems in an ensemble data assimilation system based on an atmospheric
general circulation model (GCM), AFES, we developed an ensemble data assimilation system based
on a coupled atmosphere-ocean GCM, CFES. A prototype of the system has been constructed, in
which atmospheric observational data (NCEP PREPBUFR) are assimilated every 6 hours to update
the atmospheric variables, whereas the oceanic variables are kept unchanged throughout the
assimilation procedure. The analysis-forecast cycle starts on August 1, 2008, and the atmospheric
initial conditions (40 members) are taken from ALERA2, the second generation of AFES-LETKF
experimental ensemble reanalysis (ALERA). Two cases of experiment are carried out with different
oceanic initial conditions. In one case, outputs from a stand-alone oceanic simulation on August 1 from
1967 through 2006 are used as the 40-member oceanic initial conditions. As a result of large
perturbations at the ocean surface, replacement of AFES with CFES successfully contributes to
increased ensemble spread in the lower troposphere. In the other case, a single oceanic initial
condition is used for all the ensemble members. Although surface perturbations do not grow
sufficiently to affect the atmospheric ensemble spread during the two months of the experiment,
interesting features of the oceanic ensemble spread are found such as localization along the depth of
thermocline and asymmetry between summer and winter hemispheres.
Page | 216
B7.3b - Atmosphere and UT/LS Interactions
09.07.2013 10:15-11:45, Sertig
347
Aerosol-cloud interaction from local, regional, to global scales
1
2
Renyi Zhang , Yuan Wang
1
2
Texas A&M University, Bryan, United States, TAMU, Bryan, United States
Aerosols interact directly and indirectly with the Earth´s radiation budget and climate. For the direct
effect, aerosols scatter and absorb solar radiation. Light scattering by aerosols changes the radiative
fluxes at the top-of-atmosphere (TOA), at the surface, and within the atmospheric column, while
aerosol absorption modifies the atmospheric temperature structure, decreases the solar radiation at
the surface, and lowers surface sensible and latent fluxes, suppressing convection and reducing cloud
fraction. Also, aerosols indirectly impact climate by altering cloud development, lifetime, precipitation,
and albedo. Current understanding of the aerosol indirect effect remains highly uncertain, constituting
the greatest uncertainty in climate predictions. Anthropogenic aerosols may influence the cloud
processes and precipitation by serving as cloud condensation nuclei (CCN. In this presentation, the
effects of aerosols on various cloud systems, ranging from isolated cumulus clouds, mesoscale squall
lines, to Pacific storm track, will be discussed to demonstrate the response of clouds and precipitation
to an increase in aerosol concentrations.
Page | 217
1274
Remote sensing of the UTLS in the microwave wavelengths range
1
1
Jo Urban , D. Murtagh
1
Chalmers University of Technology, Göteborg, Sweden
Millimetre-wave limb sounding instruments dedicated to middle atmospheric research were
successfully employed since the early nineties. The first instrument was the "Microwave Limb
Sounder" (MLS), launched on board the "Upper Atmosphere Research Satellite" (UARS) in
September 1991. The "Millimeter-wave Atmospheric Sounder" (MAS), targeting similar frequency
bands, made limb observations from the Space Shuttle´s cargo bay during three short missions in
1992, 1993, 1994. These instruments were equipped with double sideband Schottky-diode heterodyne
radiometers operating around 60 GHz (O2) and in the 183-205 GHz range. First limb observations in
the sub-millimetre wavelengths range were made by the Sub-Millimetre Radiometer (SMR) on board
the Odin satellite which was launched in 2001. The SMR instrument, more sensitive than its
predecessors, consists of four mechanically cooled single sideband Schottky-diode receivers in the
486-581 GHz range and one millimetre receiver at 119 GHz (O2). The Microwave Limb Sounder
(MLS) on Aura was launched in July 2004, equipped with Schottky-diode double sideband radiometers
operating in the millimetre, sub-millimetre, and far infra-red spectral ranges. Whilst the aforementioned
heterodyne limb sounders are all based on Schottky-diode heterodyne detectors, the Japanese SubMillimeter Limb Emission Sounder (SMILES) employed 5-10 times more sensitive sub-mm SISdetector. SMILES made limb observations from the International Space Station between October 2009
and April 2010.
Future limb sounders such as STEAM (Stratosphere-Troposphere Exchange And climate Monitor) are
currently being developed for sounding of the UT/LS altitude region. STEAM will use robust wideband
Schottky-radiometers in the 320-360 GHz range in combination with a tomographic multi-beam limb
sounding approach for best horizontal and vertical resolution and sensitivity.
The presentation will give an overview of measurement capabilities of past, present, and planned
microwave limb sensors with focus on the UT/LS altitude region.
Page | 218
837
Global upper tropospheric/lower stratospheric water vapor and isotopologues
from satellites
1
1
1
2
3
Gabriele Stiller , Stefan Lossow , Michael Kiefer , William G. Read , Karen H. Rosenlof , Maya
4
5
6
7
8
Garcia-Comas , Mark E. Hervig , Gerald Nedoluha , Ellis E. Remsberg , James M. Russell , Larry W.
7
9
10
11
11
7
Thomason , Joachim Urban , Kaley A. Walker , Mark Weber , Katja Weigel , Joseph M. Zawodny
1
Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology (KIT), Eggenstein2
Leopoldshafen, Germany, Jet Propulsion Laboratory, California Institute of Technology, Pasadena,
3
United States, Chemical Science Division, NOAA Earth System Research Laboratory, Boulder,
4
5
United States, Instituto de Astrofisica de Andalucia-CSIC, Granada, Spain, GATS Inc., Driggs,
6
7
United States, Remote Sensing Physics Branch, NRL, Washington, United States, NASA Langley
8
Research Center, Hampton, United States, Atmospheric and Planetary Sciences Faculty, Hampton
9
University, Hampton, United States, Department of Earth and Space Sciences, Chalmers University
10
of Technology, Gothenburg, Sweden, Department of Physics, University of Toronto, Toronto,
11
Canada, Institute for Environmental Physics, University of Bremen, Bremen, Germany
The past decade has been a "golden age" for observations of middle atmospheric trace gas
distributions from space since numerous satellite instruments have been in orbit. One of the most
important trace species with respect to its impact on global climate and stratospheric chemistry is
water vapor. The presentation will provide an overview on the currently available data base, and on
climatologies derived from the satellite data sets covering the altitude range from the upper
troposphere to the lower mesosphere. The current and planned efforts within the SPARC Water Vapor
Assessment II (WAVAS II) to intercompare the available satellite data sets and perform a quality
assessment will be presented, with some focus on the difficulties which we are facing on the way to a
consistent multi-instrument long-term data set covering the last 30 years. We will also discuss the
distribution of water vapor isotopologues, mainly HDO, which can be derived from satellite data, and
what can be learned from those about the transport of water vapor from the troposphere into the
stratosphere, including phase transition processes (convective processes, freeze-drying, and
overshooting of ice particles).
Finally, future perspectives for the continuation of middle atmosphere water vapor observations from
space will be discussed.
Page | 219
1093
Observations of aerosol and cloud from limb and occultation measurements
using SCIAMACHY
1
1
1
1
1
1
John Burrows , Alexij Rozanov , Katja Weigel , Florian Ernst , Kai-Uwe Eichmann , Lena Brinkhoff ,
2
Christian von Savigny
1
2
University of Bremen, Institute of Environmental Physics, Bremen, Germany, Ernst-Moritz-ArndtUniversität Greifswald, Institut für Physik, Greifswald, Germany
SCIAMACHY (Scanning Imaging Absorption spectrometer for Atmospheric CHartographY) is a
national contribution to ESA Envisat, which flies in a sun synchronous orbit at 775 km altitude in
th
descending mode and having an equator crossing time of 10:00 am. Envisat was launched on the 28
February 2002 and measurements were downlinked until contact to the satellite was suddenly lost on
th
the 8 April 2012. SCIAMACHY made measurements of the scattered solar radiation up welling from
the top of the atmosphere in alternate nadir and limb viewing geometry and also during solar and lunar
occultation. This presentation will focus on the limb and occultation measurements and their use to
retrieve aerosol and cloud products from SCIAMACHY. One focus will be the observations of PSC and
aerosol in the Upper Troposphere and Lower stratosphere.
Page | 220
1013
Significant responses of stratospheric ozone and atmospheric dynamics to a
small perturbation of brominated VSLS halocarbons
1
1
1
1
2
1
1
1
Xin Yang , L. Abraham , A. Archibald , P. Braesicke , J. Keeble , P. Telford , N. Warwick , J. Pyle
1
2
NCAS, University of Cambridge, Cambridge, United Kingdom, University of Cambridge, Cambridge,
United Kingdom
We used a whole atmosphere (troposphere + stratosphere) chemistry-climate model UMUKCA to
investigate the role of very short-lived substances (VSLS) on stratospheric bromine budget and ozone.
A pair of 20-year long integrations (with VSLS emissions switched on and off) shows the stratospheric
ozone response to the changes of VSLS emission is very complex due to climate-chemistry
feedbacks. A significant ozone loss (more than 20%) in the lowermost stratosphere of the southern
hemisphere is modelled after introducing brominated VSLS, which is due to the acceleration of
heterogeneous reactivation of Cl- on polar stratospheric clouds (PSCs) through Br-Cl cross reactions
(e.g. HOBr+Cl- produces BrCl). This significant ozone reduction is also associating with air
temperature drops by up to ~2 degrees Celsius due to a reduction in radiative heating. Significant
increases in tropopause (up to 400 m) in southern hemisphere polar region and reductions of age of
air (up to 1 month) in regions just above the tropopause are associated with the significant ozone
losses.
Comparing with model run without VSLS emissions, the atmospheric column ozone is reduced by
several Dobson Units (DUs) in low latitudes and up to tens DUs in mid- to-high latitudes. In
stratosphere, specially variable positive ozone responses (a few percentage) are simulated, reflecting
dynamic effects; the large ozone loss affects radiative heating and alters the Brewer-Dobson
circulation, which in turn affects chemistry and eventually results in a 'new' equilibrium of ozone
distribution. A similar dynamical response is also seen in another experiment in which PSCs were
arbitrarily removed. Our model result indicates that the climate system is sensitive to chemical
perturbation, even to perturbations as small as few pptv of brominated VSLS halocarbons. The
sensitivities of ozone responses to changing VSLS emissions at different stratospheric chlorine levels
are also performed.
Page | 221
C4.1b - Meteorological forcing data and distributed modelling of snow, ice and
hydrology in mountain watersheds
09.07.2013 10:15-11:45, Sanada I
1033
Spatio-temporal sensitivities of a physically based distributed snow model to
forcing meteorological model scales
1
1
2
Adam Winstral , Danny Marks , Robert Gurney
1
2
USDA-ARS-NWRC, Boise, United States, ESSC, University of Reading, Reading, United Kingdom
Highly heterogeneous mountain snow distributions strongly affect soil moisture patterns, local ecology,
and ultimately the timing, magnitude, and chemistry of stream runoff. Capturing these vital
heterogeneities in a physically-based distributed snow model (DSM) requires appropriately scaled
model structures. In the face of global climate change, the call for application of these types of models
over broader regions has intensified. However upscaling the spatial coverage of these models often
requires consequent downscaling of model complexity and resolution to meet computational
capabilities. This work looks at how model scale - particularly the scales at which the forcing
processes are represented - affects simulated snow distributions and melt. Quite often the
computational cost associated with modeling the many forcings is much greater than the actual snow
and melt modeling. While the scaling properties of snow distributions have been examined in some
detail, the scaling characteristics of the forcing processes and their effects on snow modeling have
received little attention. The processes mainly responsible for snow distribution heterogeneity in this
region - wind speed, snow accumulation, and solar radiation - were independently re-scaled to test
process-specific spatio-temporal sensitivities. Synthetic vegetation and terrain structures were created
to similarly test the influence of these features on scale-induced effects. We found that whereas the
snow cover needs to be adequately resolved to a characteristic length scale, this was not always true
for the forcing processes. The required scales were a function of process, weather, and seasonality.
Appropriate scales for the radiation forcings - both solar and thermal - were directly related to the
scaling of canopy features. Computational costs could be considerably reduced with minimal effects
on model accuracy with process- and time-appropriate upscaling. It was also shown that when
autocorrelation between snow accumulation and energy fluxes exists, scale degradation produces
characteristic temporal biases in runoff simulations.
Page | 222
1220
Improving rainfall and temperature estimations in complex topography: an
application in the Swiss Alps
1
1
2
3
1
Cara Tobin , Ludovico Nicotina , Alexis Berne , Marc B. Parlange , Andrea Rinaldo
1
2
3
ECHO, EPFL, Lausanne, Switzerland, LTE, EPFL, Lausanne, Switzerland, EFLUM, EPFL,
Lausanne, Switzerland
The characteristic spatial scales of temperature and precipitation forcings are poorly captured by
sparse measurements within complex topography. To improve the interpolation of such forcings during
extreme precipitation events, this study has integrated digital terrain information and a weather
forecast model with sparse gauge data. Three flood events in the Swiss Alps were analyzed to
determine the factors which have the greatest influence on intense precipitation induced by orographic
effects. The goal of this research was to improve the precipitation and temperature inputs to the
MINERVE hydrological model, the semi-distributed flood forecasting model used operationally in the
Valais region of Switzerland. Up until this point, this model has poorly estimated the impact of floods
which have caused damage to the region on the order of millions of Swiss francs.
In this study, interpolation techniques have been compared: Inverse Distance Weighting, Ordinary
Kriging, and Kriging with External Drift (KED). The kriging geostatistical methods relied on a robust
and resilient variogram accounting for anistropy. Results indicate that using numerical weather
forecast and elevation data as covariates for precipitation, KED has lower errors at the cost of higher
estimation variations. Most notably, orographic effects were captured by KED at high elevations where
precipitation was noted during extreme events, yet was not previously captured with measurement
stations routinely used in the operational rain gauge network. Moreover, the use of elevation as
auxiliary information in the KED of temperatures demonstrated minimal errors relative to the other
interpolation methods. These results indicate that KED for temperature outperforms the other methods
during extreme events due to its consideration of instantaneous lapse rates. Furthermore, the
incorporation of the improved temperature and precipitation input fields into the hydrological model
provided outputs in agreement with measured discharge volumes and flood peaks for the events
analyzed.
Page | 223
1069
Sensitivity of a land surface model to total water input and meteorological
forcing data generation
1
1
2
2
2
Andrew Newman , Martyn P. Clark , Danny Marks , Adam Winstral , Annelen Kahl
1
2
RAL/HAP, National Center For Atmospheric Research (NCAR), Boulder, United States, NWRC,
USDA-ARS, Boise, United States
With limited observations in complex terrain, techniques are needed to distribute meteorological
forcing data to land surface models (LSMs). Two approaches, an inverse distance weighting scheme
with monthly climatological elevation lapse rates (MicroMet), and a de-trended kriging approach are
used to distribute forcing data across the Reynolds Creek Experimental Watershed, Idaho, USA to the
Noah-Multi-Physics (Noah-MP) LSM. Additionally, methods to account for net snow transport are
needed in most LSMs including Noah-MP, which generally do not include such processes. Explicit
snow distribution models (i.e. SnowModel or Alpine3D) are one avenue to generate estimates of net
snow transport. Another method relies on more basic terrain based parameters, which is necessary
when running a fully distributed high-resolution snow-transport model is impractical (e.g. large
watersheds). Differences in the forcing data and net snow transport estimates can lead to substantial
differences in model output for mountain watersheds.
Initial results show that variations in precipitation and net snow transport, or the total water input (TWI),
drive the bulk of variability in the watershed. TWI variations impact runoff hotspots, spring and summer
soil moisture, and surface fluxes. During the peak runoff month of May, variations in monthly runoff of
over 40% are seen, while differences in daily runoff can be greater than 60%. There are also
sometimes substantial differences in the location of TWI maxima. This results in spring-summer
averaged soil moisture differences that are commonly 10-30% in these regions. Differences in the
other meteorolgoical forcing data impact these variables to a lesser degree.
Page | 224
712
Data driving us to distraction - where to focus attention for snow and stream
simulations in complex terrain
1
2
3
3
3
3
Jessica Lundquist , Nicoleta Cristea , Nic Wayand , Shara Feld , Brian Henn , Karl Lapo , Laura
3
Hinkelman
1
2
Civil and Environmental Engineering, Univeristy of Washington, Seattle, United States, University of
3
Washington, Seattle, United States, Univeristy of Washington, Seattle, United States
2
At spatial scales relevant to local and regional planning processes (100 to 1000 km ), the inaccuracy
and uncertainty in meteorological driving data in mountain watersheds have been major obstacles to
producing defensible hydrologic model simulations. Here we use distributed measurements and
modeling in the American River and Tuolumne River Basins in the Sierra Nevada, California to
demonstrate 1) our current ability to produce spatially-distributed fields of precipitation, temperature,
relative humidity, solar radiation, and longwave radiation; 2) their relative impacts and inter-relations
on modeling snow and basin hydrology; and 3) best paths forward utilizing mesoscale atmospheric
models, distributed sensor technology, and remote sensing for both model forcing and model
validation.
Page | 225
B4.1b - Global monsoon system: past, present and future
09.07.2013 10:15-11:45, Aspen I
305
Recent advances in dynamics study on the Asian summer monsoon onset
1
Guoxiong Wu
1
LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
Compared with 850hPa-wind, the surface-wind can better depict the onset of the Asian Summer
Monsoon (ASM) systems. It demonstrates that the onset of the Tropical ASM (TASM) first occurs over
the southeastern Bay of Bengal (BOB) in May. Then it propagates eastward to the Indochina
Peninsula and reaches the South China Sea (SCS) in mid-May and the tropical North West Pacific
(NWP) in early-June. To the west of the BOB, monsoon onset starts near the equatorial Arabian Sea,
then propagates northward, representing the Indian Summer Monsoon onsets. In addition, the
Subtropical Asian Summer Monsoon (STASM) establishes firstly over the NWP, then expands
westward and merges into the precipitation zone over the SCS in early June, forming a northeastsouthwest rain-belt. Almost as the same time, the summer monsoon lands the southeastern China and
the Baiu in Japan also starts. Afterwards, the rainfall-belt shifts northward to the Yangtze River and the
Korea in mid June, corresponding to the start of the Meiyu and Changma.
This talk also reviews some recent progresses of dynamics studies on the ASM onset. In spring, an
evanescent but strong warm pool is formed in the central-eastern BOB due to the combined forcing of
the Tibetan Plateau and the land-sea distribution in South Asia. Driven by the pumping effect of the
South Asian High (SAH), a Onset Vortex usually, develops over the eastern BOB, resulting in the first
onset of TASM over the BOB. Furthermore, the vertical easterly/westerly shear over the
eastern/western BOB prompts/inhibits the convection and increases/decreases the surface sensible
heating transferring from ocean to atmosphere, resulting in a monsoon onset barrier over the west
coast of BOB. Hence the monsoon onset can expand only eastward and it is followed by the
successive onset of SCS and tropical west Pacific summer monsoon.
Page | 226
765
Advanced Asian summer monsoon onset in recent decades
1
Yoshiyuki Kajikawa
1
RIKEN, Advanced Institute for Computational Science, Kobe, Japan
The significant seasonality in long-term trends in the Asian monsoon on a monthly mean basis is
elucidated. Advanced monsoon onsets over the Bay of Bengal and the western Pacific were evident in
recent decades. Increasing rainfall in May along 10°N reflected the advanced monsoon onset.
Decreasing rainfall trends in June along 10°N were also detected. Because the rainfall trends in July
and August showed less significance, the monsoon transition phase should be discussed in the
context of climate change rather than boreal summer mean field. Two different mechanisms for the
advanced monsoon onset are proposed. Over the continental monsoon region, the advanced
monsoon onset and weakening of the monsoon during early summer are most likely to be attributed to
the heat contrast between the Asian landmass and the tropical Indian Ocean. The heating trend over
the Asian landmass primarily contributes to the heat contrast variability with the persistent SST
increase in the Indian Ocean throughout the season (Kajikawa et al., 2012). On the other hands, over
the western North Pacific area, the advanced onset is affected by the enhanced activity of tropical
cyclones and intraseasonal variability. These are attributed to a significant increase in SST over the
equatorial western Pacific from 1980s to 2000s (Kajikawa and Wang 2012).
Page | 227
303
The effects of asymmetric potential vorticity forcing on the instability of South
Asia High and Indian summer monsoon onset
1
1
Yimin Liu , Y. Zhang
1
LASG, Institute of Atmospheric Physics, Beijing, China
Based on the theory of potential-vorticity (PV), the unstable development of the South Asia High (SAH)
due to diabatic heating and its impacts on the Indian Summer Monsoon (ISM) onset are studied via a
case diagnosis of 1998.The Indian Summer Monsoon onset in 1998 is related to the rapidly
strengthening and northward moving of a tropical cyclone originally located in the south of Arabian
Sea. It is demonstrated that the rapid enhancement of the cyclone is a consequence of a baroclinic
development characterized by the phase-lock of high PV systems in the upper and lower troposphere.
Both the intensification of the SAH and the development of the zonal asymmetric PV forcing are forced
by the rapidly increasing latent heat released from the heavy rainfall in East Asia and South East
Asian after the onsets of the Bay of Bengal monsoon and the South China Sea monsoon. High PV
moves southwards along the intensified northerlies on the eastern side of the SAH and travels
westwards on its south side, which can reach its northwest. Such high PV eddies are transported to
the west of the SAH continuously which is the main source of PV anomalies in the upper troposphere
over Arabian Sea from late spring to early summer. A cyclonic curvature on the southwest of the SAH
associated with increasing divergence, which forms a strong upper tropospheric pumping. The cyclone
in lower troposphere moves northwards from low latitudes of Arabian Sea, and the upper-layer high
PV extends downwards and southwards. Baroclinic development thus occurs and the tropical lowpressure system develops into an explosive vortex of the ISM. In addition, the evolution of subtropical
anticyclone over Arabian Peninsula associated with the very strong surface sensible heating on
Arabian Peninsula is another important factor contributing to the onset of the ISM.
Page | 228
319
The effect of an increased convective entrainment rate on Indian monsoon
biases in the Met Office Unified Model
1,2
1
1
2
Stephanie Bush , Andrew Turner , Steve Woolnough , Gill Martin
1
2
Department of Meteorology, NCAS-Climate, University of Reading, Reading, United Kingdom, UK
Met Office, Exeter, United Kingdom
Global circulation models (GCMs) are a key tool for understanding and predicting monsoon rainfall,
now and under future climate change. However, many GCMs show significant, systematic biases in
their simulation of monsoon rainfall and dynamics that spin up over very short time scales and persist
in the climate mean state. We describe several of these biases as simulated in the Met Office Unified
Model and show they are sensitive to changes in the convective parameterization´s entrainment rate.
To improve our understanding of the biases and inform efforts to improve convective
parameterizations, we explore the reasons for this sensitivity. We show the results of experiments
where we increase the entrainment rate in regions of especially large bias: the western equatorial
Indian Ocean, western north Pacific and India itself. We use the results to determine whether
improvements in biases are due to the local increase in entrainment or are the remote response of the
entrainment increase elsewhere in the GCM. We find that feedbacks usually strengthen the local
response, but the local response leads to a different mean state change in different regions. We also
show results from experiments which demonstrate the spin-up of the local response, which we use to
further understand the response in complex regions such as the Western North Pacific. Our work
demonstrates that local application of parameterization changes is a powerful tool for understanding
their global impact.
Page | 229
206
What happen when Meiyu heating changes: a numerical study
1
2
1
1
3
Qing Bao , Jing Yang , Yimin Liu , Guoxiong Wu , Bin Wang
1
2
3
IAP, Beijing, China, Beijing Normal University, Beijing, China, University of Hawaii at Manoa,
Honolulu, United States
Observational evident has shown that there is a change of Meiyu heating during the last 50 years, and
this change is associated with South China flood. The possible affects of the change of Meiyu heating
has been studied with an linearized Atmospheric General Circulation Model (AGCM). An anomalous
thermal forcing has been added in the model under the background of the mean state of the boreal
summer, then the steady state of the numerical experiment reveals that the change of the Meiyu
heating, on the one hand, induce to intensification of the subtropical rain-belt over Japan; on the other
hand, the change of the Meiyu heating may partly induce the North China drought.
The mechanism of their linkages has been proposed: the Meiyu heating excites a group of Rossby
wave train in the upper troposphere, which propagates eastward; the cyclonic anomaly induced by the
Meiyu heating elongates southwest-northeastward tilted along the East Asian Subtropic front; both the
upper-level barotropic structure and lower-level circulation changes lead to the intensification of the
lower-level moisture transport over East Asia and strengthening of the rainfall over Changma in
Korean and Baiu in Japan; consequently, the Meiyu Heating leads to the upward vertical motions over
the subtropical front of EA in 500mb, then the anomalous upward vertical motions lead to the
subsidence in North China, which can be explained by the theory of 'Sverdrup' vorticity balance, and
this subsidence may partly contribute to North China drought.
Page | 230
A4.2c - Sea ice and Ocean-Atmosphere Interactions
09.07.2013 13:15-14:45, Sanada II
514
The role of sea ice in Southern Hemisphere reanalysis trends prior to 1979
1
2
3
1
Sam Dean , James A. Renwick , Gilbert P. Compo , Michael J.M. Williams
1
2
3
NIWA, Wellington, New Zealand, University of Victoria, Wellington, New Zealand, CIRES, University
of Colorado, Boulder, United States
Reanalysis data products such as the 20th Century Reanalysis Project (20CR) represent our best
understanding of the weather and climate that existed for the last century. The 20CR project produced
a 6 hourly reconstruction of atmospheric circulation for the entire 20th Century by assimilating only
station records of mean sea level pressure. This approach helps to reduce the discontinuity that
occurs in reanalysis products associated with the introduction of satellite data around 1979. From the
1950s to the 1980s the 20CR , along with all other reanalysis products, exhibits a moderately strong
trend of increasing surface pressures in the Southern Hemisphere mid-latitudes and decreasing
surface pressures over the South Pole. This is reflected in a positive trend in the Southern Annular
Model (SAM) when derived from the reanalysis data. As has been demonstrated by many authors,
station records available for this time period do not indicate that any significant or coherent trends in
surface pressure actually occurred. We show here that the trend in the 20CR originates from model
forcings in conflict with the assimilated observations. Two of the prominent model forcings, sea surface
temperature and sea ice, were largely unobserved in the Southern Ocean prior to the advent of
satellites. To investigate the role of sea ice in the pressure trends we present a statistical
reconstruction of Antarctic sea ice extent, which is based only on atmospheric pressure
measurements. This reconstruction does not demonstrate the stark decrease in sea ice extent from
the 1950s to the 1980s seen in the HadISST sea ice reconstruction used by 20CR, and elsewhere.
We demonstrate, via simulations of a global atmospheric climate model, that the trends in mean sea
level pressure and the SAM are approximately halved when the statistical sea ice reconstruction is
used in place of the HadISST dataset.
Page | 231
467
On the role of sea-ice transport for Southern Ocean stratification in the past,
present, and future
1
1
Alexander Haumann , Matthias Münnich , Nicolas Gruber
1
ETH Zurich, Zürich, Switzerland
1
The formation, subsequent lateral transport, and melt of sea ice represents a key process for the
determination of upper ocean stratification in the Southern Ocean. Sea ice is transported northward in
large parts of the Southern Ocean by strong near-surface winds and melts along the ice edge south of
the polar front, an important upwelling region. Here, it adds freshwater to the surface ocean, lowers
the sea-water density, and possibly reduces upwelling by increasing the stratification. Consequently,
this redistribution of freshwater in time and space affects the vertical overturning circulation which is an
important determinant of the ocean-atmosphere CO2 exchange and, thus, of the global climate. We
investigate the Southern Ocean sea-ice ocean system using satellite observations together with
simulations with a newly developed regional ocean sea-ice model on the basis of ROMS. Satellite
derived sea-ice area transport shows that the freshwater transport is large in the Weddell and Ross
Seas where sea ice extends to its lowest latitudes. We assess the importance of this freshwater
transport for the stratification and circulation by perturbing our model simulations for past, present, and
potential future climate conditions.
Page | 232
784
Atmospheric controls on Antarctic sea ice variability
1
2
3
James Renwick , Sam Dean , Alison Kohout
1
2
Physical Geography, SGEES, Victoria University of Wellington, Wellington, New Zealand, Climate
3
research, NIWA, Wellington, New Zealand, NIWA, Christchurch, New Zealand
Antarctic sea ice extent is modulated by atmospheric circulation anomalies on daily to seasonal time
scales. This presentation will review our understanding of such interactions and will discuss the
relative importance of thermal (heat flux) and mechanical (ice motion) effects upon regional sea ice
variability on weekly to seasonal time scales. Longer-term trends in sea ice extent appear to be driven
both by oceanic and atmospheric circulation, which themselves are coupled on interannual time
scales. This presentation will discuss the extent to which observed trends in Antarctic sea ice extent
can be attributed to decadal-scale variations in Southern hemisphere atmospheric circulation, on the
basis of observational data sets.
Page | 233
1091
Antarctic sea ice persistence and climate response to an increase in
concentration and thickness considering different sea ice model complexities
1
1
2
Claudia Parise , Luciano P. Pezzi , Kevin I. Hodges
1
2
National Institute for Space Reseach, Sao Jose dos Campos, Brazil, University of Reading, Reading,
United Kingdom
This study aimed to analyze the climate signal generated by imposing an extreme positive condition of
Antarctic sea ice considering different complexities of the sea ice model. First, the sea ice is
represented by a dynamic model of three layers which vary in accordance with the processes of
conservation of energy and momentum. In the second case, the sea ice dynamics component was
neglected and the model is represented in a single layer whose variability depends exclusively on
thermodynamic processes. The model used was the CM2.1 Climate Model developed by Geophysical
Fluid Dynamics Laboratory. In order to isolate the climate signal generated by the change in the
Antarctic sea ice initial condition to the climate response due to the sea ice model complexity, four
numerical experiments were conducted. Two of them considered a sea ice sophisticated model and
the others two considered a sea ice simplified model whose differences within them were concentrated
in the Antarctic sea ice initial condition, i.e., maximum and climatological for each case. The whole
Antarctic sea ice pack has showed a loss of its persistence around 12 months, but in some regions in
4-5 months the sea ice was thin enough to open and put the warmer ocean in contact with the
atmosphere what highlights the clear regional variability of the Antarctic sea ice persistence time. The
Bellingshausen and Amundsen Seas and Indian Ocean, which exhibit the smaller climatological
extend of sea ice, were the sectors that preserved this maximum for more time. The maximum sea ice
imposed as initial condition has produced negative anomalies of temperature and salinity in the
extratropicial latitudes which moved toward deeper sub-surface layers and toward lower latitudes as
well as cooled the extratropical atmosphere increasing the meridional temperature gradiente.
Page | 234
816
Airborne observations of the boundary layer structure in Antarctic Sea ice
zones
1
1
1
1
Alexandra Weiss , John King , Tom Lachlan-Cope , Russ Ladkin
1
British Antarctic Survey, Cambridge, United Kingdom
Airborne observations of the atmospheric boundary layer in the Antarctic Sea ice zone were
conducted in austral summer months. The study which based on these observations had two main
goals: First, to investigate the influence of various sea ice conditions on the energy and radiation
budget in different Antarctic sea ice zones. Second, to investigate the parameterization of boundary
layer and sea ice processes for different sea ice conditions. We determined values which are
representative for certain sea ice zone adjacent to the Antarctic Peninsula. For the testing and
validation of model parameterizations we determined typical areal-averaged effective boundary layer
and surface parameters. We determined the effective temperature zT_eff and aerodynamic roughness
lengths zo_eff of non homogenous sea ice as they are needed as input parameter for the bulk
parameterization of turbulent fluxes in numerical models. zT_eff and zo_eff are highly variable in the
Weddell and Bellingshausen Sea ice areas. The observations clearly show that the parameterization
assumption, that the temperature and aerodynamic roughness lengths have the same value, can
cause large errors in the model output of the turbulent heat and momentum fluxes. Moreover, we
determined the effective radiative fluxes over various sea ice conditions and investigate the
parameterization of sea surface albedo with surface temperature data. The sea surface albedo of the
Weddell and Bellingshausen Sea ice areas showed significant regional differences and the effective
sea surface albedo varied between 0.13 and 0.81. In general, the aircraft data indicate that the surface
albedo of the sea ice areas adjacent to the Antarctic Peninsula was inverse related to the sea surface
temperature. Quality assessments of commonly used temperature-albedo parameterization schemes,
which are based on this functional relation, showed that different functions are appropriate for certain
sea ice areas adjacent the Antarctic Peninsula.
Page | 235
C6.2a - Avalanche formation and forecasting
09.07.2013 13:15-14:45, Aspen II
1216
On the failure behaviour of depth hoar
1
1
Ingrid Reiweger , Jürg Schweizer
1
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland
Understanding the failure behaviour of weak snow layers is essential for modelling and predicting drysnow slab avalanches. We therefore performed laboratory experiments with snow samples containing
a weak layer consisting of depth hoar. During these experiments the samples were loaded until
fracture. We measured the deformation at the side of the samples with a high-speed camera. The
fracture process within the weak layer could thus be studied in detail. We found a fracture in shear
immediately followed by a collapse of the weak layer. In addition, we measured acoustic emissions to
find an indication of imminent failure. According to our experiments the most promising acoustic
parameter for predicting snow failure seems to be the exponent β of the cumulative size-frequency
distribution ('survival curve') of event energy. In a stable state β takes a constant value of about three.
At the occurrence of instabilities the β curve deviates from the constant behaviour and exhibits distinct
'dips', indicating that the power law behaviour of the distribution is not fulfilled anymore. Studying the
temporal evolution of the exponent β could therefore provide useful information on snowpack stability.
Page | 236
934
Using particle tracking velocimetry to measure the mechanical properties of
snow relevant for dry-snow slab avalanche release
1
2
3
1
4
5
Alec van Herwijnen , Ned Bair , Karl Birkeland , Benjamin Reuter , Ron Simenhois , Bruce Jamieson ,
1
Jürg Schweizer
1
2
WSL – Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland, US Army Corps of
3
Engineers Cold Regions Research and Engineering Laboratory, Hanover, United States, USDA
4
Forest Service National Avalanche Center, Bozeman, United States, Coeur Alaska, Juneau, United
5
States, University of Calgary, Calgary, Canada
Particle tracking velocimetry (PTV) is a widely used measurement technique to determine the
displacement and velocity of particles from video recordings. The technique has the advantage of
being largely nonintrusive and being capable of simultaneously measuring the state of deformation
over an entire cross section of the sample. PTV has been used to study the deformation and fracture
of snow in field and laboratory experiments since the mid 1990s. While initial studies focused mainly
on documenting weak layer collapse and fracture propagation velocities, recent advances now allow
the determination of essential mechanical properties relevant to snow slab avalanche release. On a
more practical side, PTV has also been used to study the mechanics of various stability tests, such as
the Propagation Saw Test or the Extended Column Test, highlighting similarities as well as certain
limitations of these tests. We will give an overview of field experiments performed in Canada, USA and
Switzerland over the last 10 years, with a particular view on relating the material properties of snow to
commonly observed snow cover characteristics, such as snow density and grain type. While PTV has
improved our understanding of the fundamental processes involved in snow fracture, we will also
highlight areas which thus far have received little attention.
Page | 237
499
Segmentation of snow grains from microtomographic data to derive the
specific grain contact area as a mechanical indicator
1
2,3
2
1
1
Pascal Hagenmuller , Xi Wang , Frederic Flin , Guillaume Chambon , Mohamed Naaim
1
2
UR ETGR, Irstea, Centre de Grenoble, Saint Martin d'Hères, France, CEN, Météo-France, CNRS,
3
Saint Martin d'Hères, France, LIRIS, Université de Lyon, CNRS, Villeurbanne, France
The concept of snow grain is commonly used in the snow community, either in situ to identify the type
of snow or in numerical modeling to reproduce the physical and mechanical behavior of the snowpack.
The specific grain contact area (SGCA) has long been believed to be a relevant mechanical indicator.
Similarly to the specific surface area which measures the surface of exchange with the environment,
SGCA measures the surface of force exchange between grains.
The snow grains can be studied using 2D sections or images of individual grains taken from the
snowpack. Nevertheless, this reduced representation of microstructure fails to reproduce the 3Dconnectivity between grains.
The 3D microstructure of snow is available via X-ray micro-tomography. However, usual
decomposition algorithms have difficulties to separate individual grains from 3D assemblies of
particles with various shapes and contact topology. Recently, «curvature-based» segmentation
algorithms, where the necks are defined as negative Gaussian curvature zones, have shown
promising results on 3D snow images. Nevertheless, the way in which the surface information
(negative curvature) is spread into the volume (Voronoi diagram; fire front´s propagation) yields
twisted contact surfaces with over-estimated areas. We propose a new approach that propagates the
grain seeds obtained by the curvature-based algorithm while minimizing the overall grain contact area.
This criterion is relevant for further mechanical considerations where the "weakest necks" are
determinant.
This algorithm is successfully applied to 3D snow images and compared to the curvature-based
algorithm. A similar number of grains is detected but the computed SGCA is significantly lower with
our approach. Moreover, the minimization of the contact area makes our approach robust, in particular
when over-segmentation occurs in the curvature-based algorithm. Finally, our algorithm is used to
derive the evolution of the SGCA with metamorphism.
Page | 238
212
Snow avalanches genetic types derived from spatial modeling of snowpack
structural instability on Olympic slopes 2014, Western Caucasus, Russia
1
Elena Klimenko
1
The Laboratory of Snow Avalanches and Debris Flows, Lomonosov Moscow State University,
Moscow, Russian Federation
Snow avalanche formation is a result of complex interaction of variable in time, heterogeneous,
stratified snowpack and relief of underlying surface. Therefore, avalanche release should be prepared
in advance inside snowpack being a result of unstable layer/interface presence within snow structure.
It comes out with an idea of “structural instability” which was previously referred just to slabs.
Meanwhile wide variety of genetic types of snow avalanches was described in the field which are
much less considered nowadays.
In our work we extended the idea of “structural instability” linking physical conditions within snowpack,
possible mechanisms of failure and genetic types of avalanches. As a result came out with a new
classification scheme which can be used to assess the readiness of snowpack to form an avalanche of
any genetic type. The overall aim of our research is to model spatially and assess structural snow
stability with a reference to a genetic type of possible avalanches.
We introduced a complex method which allows to obtain spatial patterns of unstable snow structures
distribution at avalanche sites as output. It includes detailed morphological analysis of DTM,
meteorological data recalculation, physical modeling of snowpack, snow stability assessment using
our classification scheme, statistical analysis of modeling results.
We applied our method to model snow stability in Rosa Khutor ski resort, Western Caucasus during
the winter 2011-12. The resort is going to receive the Olympics 2014 that increases the relevance of
our research. We used Swiss model Snowpack to simulate snow cover evolution. Modeling results
were verified with snow pitting data and avalanche observations. In every site where avalanche
descends took place extensive unstable zones had been modeled. 90% of registered avalanches had
the same genetic type as we predicted with our classification scheme.
Page | 239
A6.2a - Ice sheet – ocean – atmosphere interactions
09.07.2013 13:15-14:45, Forum
385
Mass balance of the Northern Antarctic Peninsula and its response to ice shelf
loss, warming, and Ocean-driven melting
1
2
3
4
1
Ted Scambos , Etienne Berthier , Christopher A. Shuman , Alison J. Cook , Terry Haran , Jennifer
1
Bohlander
1
2
NSIDC/CIRES, University of Colorado at Boulder, Boulder, United States, CNRS/LEGOS, Université
3
de Toulouse, Toulouse, France, UMBC/JCET, NASA/Goddard Space Flight Center, Greenbelt,
4
United States, Department of Geography, Swansea University, Swansea, United Kingdom
A remote sensing assessment of the most rapidly changing areas of the northern Antarctic Peninsula
(nAP, region < 66°S) spanning the period 2003-2009 shows that ice elevation decrease and mass loss
for the region is dominated by east-flowing glaciers reacting to ice shelf losses of the past 20 years.
-1
Total mass loss from 33 glacier catchments and islands of the nAP is 23.3 +/- 5 Gt a (preliminary
estimate), or roughly 20 to 35% of the total Antarctic mass imbalance. Glaciers that had flowed into the
-1
Prince Gustav, Larsen A, and Larsen B shelf areas account for 14.3 Gt a . Mean elevation change
-1
rates exceed 2 m a for most eastern catchments. However, elevation decreases at lower rates are
widespread, including most of the western glacier catchments, and both high and low elevation
regions. Increased snowfall in the region (e.g., increasing from ~1.75 m w.e. to ~2.75 m w.e. over the
past 50 years at two ridge crest ice core sites) has not led to elevation increase, and effects of regional
climate warming on firn compaction are small relative to the observed elevation change rates. We infer
that western nAP dynamic ice flow changes, western-side ice tongue and ice shelf retreats, and
continuing effects of grounding-line melt from warm ocean conditions over the past century explains
the western nAP mass losses. Our assessment is based on both satellite stereo-image DEM
differencing (dDEMs) and ICESat-derived along-track elevation changes. To adjust along-track path
offsets between its 2003-2009 campaigns, we use a recent DEM of the Antarctic Peninsula to correct
for cross-track slope (Cook et al., 2012, doi:10.5194/essdd-5-365-2012; http://nsidc.org/data/nsidc0516.html) and some supplemental ASTER-derived DEMs for outlying islands. We reduce the effect of
possible seasonal variations in elevation by using only integer-year repeats of the ICESat tracks for
comparison and multi-year dDEMs
Page | 240
434
Rapid increase in melt rates of Pine Island Glacier Ice Shelf during early stages
of its retreat
1
1
1
Jan De Rydt , Paul Holland , Pierre Dutrieux , Adrian Jenkins
1
British Antarctic Survey, Cambridge, United Kingdom
1
Observations beneath the floating section of Pine Island Glacier have revealed the presence of a
subglacial ridge which rises up to 300m above the surrounding bathymetry. This topographic feature
has likely served as a steady grounding line position, and Pine Island Glacier was at least partially
grounded on the ridge until the early 1970s. Today the grounding line is situated approximately 30km
further upstream, following an ongoing phase of rapid retreat. As a result, a large ocean cavity has
formed behind the ridge, strongly controlling the ocean circulation beneath the ice shelf and
modulating the ocean water properties that cause melting of the ice shelf in the vicinity of the
grounding line. In order to understand how melt rates have changed during various phases of cavity
formation, we use a high resolution ocean model to simulate the cavity circulation for a series of
synthetic geometries. We show that the gap between the ridge and the bottom of the ice shelf strongly
controls the inflow of warm bottom waters into the cavity, and hence influences the melt rates. Model
results provide evidence for rapidly increasing melt rates at the onset of ice shelf thinning, but a weak
change in melt rates once the gap between the ridge and the ice shelf has passed a threshold value of
∼150m. At present the gap is well over 150m, suggesting that observed variability in melt rates is
primarily controlled by other factors such as the depth of the thermocline.
Page | 241
435
Trend of melt under Pine Island Glacier Ice Shelf modulated by high variability
in ocean temperature
1
1
1
1
2
2
Pierre Dutrieux , Jan De Rydt , Adrian Jenkins , Paul Holland , Ho Kyung Ha , Sang Hoon Lee , E.
1
3
4
Povl Abrahamsen , Stanley S. Jacobs , Michael Schroeder
1
2
British Antarctic Survey, Cambridge, United Kingdom, Korea Polar Research Institute, KOPRI,
3
Incheon, Korea, Republic of, Lamont Doherty Earth Observatory, Columbia University, New York,
4
United States, Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany
Pine Island Glacier and neighbouring outlet glaciers of West Antarctica have thinned and accelerated
over the last 2 decades, significantly contributing to global sea level rise. Increased ocean heat
transport beneath Pine Island Glacier ice shelf and unpinning from a seabed ridge are thought to be
the primary drivers of such changes. However, the acceleration of the glacier paused since 2009,
renewing questions about the main processes presently affecting the ice/ocean system, the future
behaviour of the glacier and the associated impacts. Here, we present ocean observations taken in
austral Spring 2012 to show a 200 m lowering of the thermocline at the glacier calving front and a 50%
decrease of meltwater production from 2009. High-resolution simulations of the ocean cavity beneath
the floating tongue of the glacier demonstrate that for the present ice geometry, the seabed ridge
blocks the warmest deepest waters from reaching the ice and strongly ties meltwater production to
thermocline depth above the ridge, hereby making it susceptible to relatively high variability in time,
from intraseasonal to interannual. These results highlight the fundamental importance of local ice shelf
and seabed geometry for determining ice-ocean dynamics.
Page | 242
1251
Sensitivity of sub-ice shelf melt rate parameterizations in a general circulation
model: thermodynamic versus dynamic forcing
1
1
2
Veronique Dansereau , Patrick Heimbach , Martin Losch
1
2
EAPS, MIT, Cambridge, United States, AWI, Bremerhaven, Germany
We investigate sensitivities of sub-ice shelf melt rate parameterizations in both idealized and realistic
Pine Island Ice Shelf (PIIS) configurations of the MIT general circulation model (MITgcm). In a first set,
sensitivities to changes in the formulation of the melt rate parameterization are considered, with a
focus on velocity-independent versus dependent transfer coefficients. We find significant changes in
melt rate patterns between the two cases, pointing to an important role of frictional compared to
thermal forcing at the ice/ocean interface. In a second set, adjoint melt rate sensitivities to changes in
the cavity circulation are calculated, revealing dominant pathways between the cavity exit and regions
where ocean waters can affect melting. Both results suggest large remaining uncertainties in the
spatial distribution of simulated melt rates with implications for ocean-ice shelf coupling.
Page | 243
923
Decadal variability of Petermann Gletscher, NW Greenland from observations
of ice, ocean, and atmosphere
1
2
3
4
4
Andreas Muenchow , Laurie Padman , Helen Johnson , Allan Mix , Roger Samelson
1
2
University of Delaware, Newark, United States, Earth and Space Research, Seattle, United States,
3
4
University of Oxford, Oxford, United Kingdom, Oregon State University, Corvallis, United States
Petermann Gletscher drains 6% of the Greenland Ice Sheet via an 80 km floating ice shelf that since
2010 has been reduced to 50 km. We describe observed regional ice, ocean, and atmospheric
conditions for the last decade that include two extreme events when Petermann discharged 380 km^2
or 42 Gt of ice in 2010-12. Annual discharge at the glacier's grounding line is 12 Gt/y.
Surface elevation from Lidar on two track lines flown in both 2007 and 2010 reveal that hydrostatic ice
thickness decreased by 14 m along both lines. This reduction includes surface ablation and basal melt
to give ice thickness of 150 m along the central melt-channel and 240 m along the ambient ice shelf
when averaged from the grounding line to the terminus.
Coastal air temperatures of northern Greenland and Canada indicate a warming trend of 0.1+/-0.05
C/y for the 1987-2012 period, which is more than four times the global rate. Moored ocean
temperature observations at 300-m depth outside the fjord indicate warming rates of 0.06+/-0.02 C/y.
In 2012 we observed deep water renewal within Petermann Fjord as warm waters spilled over the
400-m deep sill and plunged down more than 300-m. Deep fjord waters also freshened, consistent
with accelerated basal melt water flux that is most pronounced near the grounding line.
Prior steady state mass budgets showed that 90% of the 12 Gt/y ice flux into the fjord is lost by basal
melting of the ice shelf. Observations of changing air and ocean temperatures, ice shelf thickness, and
the recent calving events may indicate a transition to a new state. Support for this hypothesis requires
systematic observations and models of physical processes that control ice-shelf thickness, ice-shelf
coupling to grounded ice, and of system response from tidal to millennial scales.
Page | 244
1192
What controls the ocean properties at the margins of Greenland´s glaciers?
1
2
Fiammetta Straneo , David Sutherland
1
2
Woods Hole Oceanographic Institution, Woods Hole, United States, University of Oregon, Eugene,
United States
Increasing evidence suggests that ocean variability played a role in the recent acceleration of glaciers
in western and southeastern Greenland which led to doubling the ice sheet's contribution to sea-level
rise. This hypothesis is supported by the fact that the timing of the glaciers' acceleration coincided with
the recent warming of the subpolar North Atlantic and by recent measurements showing that warm,
salty waters of subtropical origin circulate rapidly through these fjords. Yet the processes regulating
the inflow and variability of warm, salty waters inside Greenland's glacial fjords and at the margins of
the glaciers are complex and largely unknown. Here, I use measurements from one major glacial fjord
in southeast Greenland and historical data to show that the ocean properties near the glacier vary
rapidly and continuously as a result of a vigorous fjord/shelf exchange. The implication is that
properties at the glaciers' margins are strongly dominated by the shelf and large scale ocean variability
and that these must be known in order to provide appropriate boundary conditions to the glacier and
ice sheet models.
Page | 245
C2.3d - Clouds, aerosols and precipitation at high latitudes
09.07.2013 13:15-14:45, Studio
428
Clouds over the Antarctic Peninsula
1
Tom Lachlan-Cope
1
British Antarctic Survey, Cambridge, United Kingdom
Recently there have been two aircraft campaigns to investigate the clouds over the Antarctic
Peninsula. Although some limited airborne measurements have been made over Antarctica in the past
these campaigns are the first real, detailed in-situ, measurements of Antarctic clouds. Here we present
results from these two campaigns. The results suggest that the total numbers of cloud particles
present are similar to those found at mid latitudes and that difference between the East and West side
of the Peninsula is negligible which would not be expected if the source of cloud nuclei were local.
The observations are compared with a limited area numerical model (PolarWRF) and it found that this
model tends to underestimate the observed clouds. On some occasions Polar WRF misses an entire
cloud layer. The errors in the model are considered and some possible improvements to
parameterisations are suggested. Finally, although here we only present observations made over the
Antarctic Peninsula during summer, we suggest how these observations may relate to rest of the
Antarctic Continent and how what future work should be carried out.
Page | 246
575
Ground-based observations of Antarctic clouds using a Rayleigh LiDAR at
Davis (69S, 78E)
1
1
Simon Alexander , Andrew Klekociuk
1
Australian Antarctic Division, Kingston, Australia
A Rayleigh lidar at Davis, Antarctica (69S, 78E) has made intermittent observations of clouds for the
last few years. Radiosondes and a co-located wind-profiling radar provide additional data with which to
characterise the clouds and the environment in which they exist. We present a case study of thin cirrus
in the wintertime upper troposphere and examine its presence in the context of the mesoscale
meteorology. We use a second case study of cloud observed from the boundary layer upward to
examine the ice and super-cooled water distribution. Using all available cases, we construct an initial
climatology of cloud parameters, including cloud top height, cloud temperature (from radiosondes) and
optical depth. We discuss our future plans for extending the suite of instruments at Davis and plans for
dedicated cloud-observing campaigns to more fully characterise clouds in coastal East Antarctica and
to provide various parameters for model validation.
Page | 247
706
Ground-based remote sensing of clouds, virga and snowfall in East Antarctica,
used for regional climate model evaluation
1
1
1
2
Irina V. Gorodetskaya , Nicole P.M. Van Lipzig , Kristof Van Tricht , Maximilian Maahn , Stefan
2
3
2
4
4
Kneifel , Alexander Mangold , Jan H. Schween , Jan T.M. Lenaerts , Michiel R. Van den Broeke
1
2
3
Catholic University of Leuven, Heverlee, Belgium, University of Cologne, Cologne, Germany, Royal
4
Meteorological Institute of Belgium, Brussels, Belgium, Institute for Marine and Atmospheric
Research, Utrecht University, Utrecht, Netherlands
Clouds play an important role in the Antarctic climate and surface mass balance acting as the source
of precipitation and strongly influencing shortwave and longwave radiative fluxes. Comprehensive
meteorological, cloud and precipitation measurements have been conducted at Princess Elisabeth
base (PE) located in the escarpment area of Dronning Maud Land, East Antarctica, using an
Automatic Weather Station and ground-based remote sensing instruments (ceilometer, infrared
pyrometer and 24 GHz vertically pointing micro-rain radar (MRR)) (ees.kuleuven.be/hydrant). An
improved processing method by Maahn and Kollias (2012) especially suited for snow observations is
applied to MRR raw measurements enabling detection of snowfall and virga precipitation with effective
reflectivity as low as -14 dBz. Ceilometer backscatter profiles are also subject to a new algorithm
improving cloud base height detection especially for ice clouds. The first measurement period
January-March 2010 reveals high frequency of low and mid-level clouds with base heights at 1-3 km
agl and base temperatures of -20°-40°C. Ceilometer backscatter profiles showed various cloud types
corresponding to these height and temperature ranges, including ice clouds with large vertical extent,
geometrically thin liquid-containing clouds, and multi-layer mixed phase clouds. Detailed analysis is
focused on 13-18 March 2010 case containing clouds of different types (ice and mixed phase clouds
with a liquid layer on top) and varying height. The case includes complex precipitation structures with
ice virga precipitations and snowfall events of different intensity and vertical extent. An output for PE
region for the selected case is extracted from the 12-year simulation of Dronning Maud Land climate
with a regional climate model, RACMO2, at horizontal resolution of 5.5 km. Evaluation of the model
using PE data is ongoing with a focus on cloud height, phase and temperature, precipitation timing,
depth and intensity, and cloud radiative forcing.
Page | 248
152
Relationships between aerosol profiles and boundary layer mixing state at high
latitude locations
1
1
Gijs de Boer , Matthew D. Shupe
1
University of Colorado, Boulder, United States
Of the uncertainties surrounding our understanding of global climate, one of the largest involves the
relationships between aerosols and clouds, and the resulting impacts on atmospheric radiation and
precipitation. Due to limited profiling of aerosol properties, traditional studies have investigated
aerosol-cloud interactions using surface aerosol measurements as a proxy for aerosol at cloud height.
For many parts of the world, clouds occur when the boundary layer is well mixed, meaning that this
assumption is not necessarily unreasonable. At high latitudes, however, the atmosphere is often very
stable. This stability limits mixing, results in a stratified atmosphere, and means that aerosol properties
between the surface and cloud height may be different from one another. Therefore, previous attempts
at quantifying aerosol-cloud interactions for Arctic clouds using surface based aerosol measurements
are difficult to interpret. In the current work, we use a variety of measurements from different high
latitude locations to demonstrate the relationship between surface and elevated aerosol properties
under different boundary layer mixing states. Mixing state will be derived from a combination of
temperature profiling devices (e.g. radiosondes) and remote sensors (e.g. Millimeter Cloud Radar),
while aerosol measurements come from both surface and aircraft-based sensors. Measurements will
come from several campaigns, including the Indirect Semi-Direct Aerosol Campaign (ISDAC), the
Mixed-Phase Arctic Clouds Experiment (M-PACE) and the Arctic Summer Cloud Ocean Study
(ASCOS). We will demonstrate under what conditions surface aerosol properties can and cannot be
used to evaluate aerosol cloud interactions for low-level Arctic clouds.
Page | 249
172
Development of an aerosol microphysical and optical model of the marine and
coastal atmosphere surface layer
1
Gennady Kaloshin
1
V.E. Zuev Institute of Atmospheric Optics Russian Academy of Sciences, Siberian Branch, Tomsk,
Russian Federation
It is known, that changes in the concentration, and distribution of cloud-active sea-salt aerosol is
important for the precipitation efficiency of clouds, change cloud amount, their properties which
influence on the radiative forcing of the climate system.
Their impact on clouds, being superimposed on the aerosol generated by an open ocean, varies
greatly with the meteorological parameters, such as wind speed.
Based on these facts the presented investigation seeks to contribute to a better understanding of
cloud-active sea-salt aerosol and optical effects of marine aerosol eventually aiming for a development
of a robust algorithm for the aerosol extinction forecast.
In the study we consider the coastal physical effects and ocean processes as functions of the wind
speed, its direction, fetch, relative humidity and altitude above the sea level. While taking into account
the variability of marine and coastal aerosols, the paper focuses on the detailed description of the
developed aerosol model and the optical properties of the aerosol. We discuss the developed
algorithm and the comparison of our results calculated by the software product MaexPro (Marine
Aerosol Extinction Profile) with available observational data.
Page | 250
285
Sub-Antarctic marine aerosol: significant contributions from biogenic sources
1
2
3
3
3
Julia Schmale , Johannes Schneider , Eiko Nemitz , Sim Y. Tang , Christine Braban , Ulrike
3
4
5
2
Dragositz , Trevor Blackall , Phil N. Trathan , Gavin Phillips
1
2
Institute for Advanced Sustainability Studies e.V., Potsdam, Germany, Max Planck Institute for
3
Chemistry, Mainz, Germany, NERC Centre for Ecology & Hydrology, Edinburgh, United Kingdom,
4
5
Kings College London, London, United Kingdom, British Antarctic Survey, Cambridge, United
Kingdom
The recently completed International Polar Year 2007-2008 has fostered significant efforts to
investigate, among other topics, aerosol characteristics at northern high latitudes. However, available
data for the Southern Hemisphere are still scarce. Regarding the specific case of marine aerosol, the
lack of information is even greater. Many questions on their specific sources, chemical nature and
evolution in the atmosphere remain unanswered.
Here, we present a detailed study on Sub-Antarctic Atlantic Ocean marine aerosol derived from eight
weeks of stationary measurements on Bird Island (54°00´S, 38°03´W) during spring/summer 2010.
Instruments were deployed to characterize the ambient sub-micron aerosol including an Aerodyne
high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The average aerosol
composition was 46 % sulphate, 4 % nitrate, 12 % ammonium and 38 % organics. The unusually high
ammonium content was due to the ammonia emissions from large fur seal and penguin colonies on
the Island (closest to the site, colonies were > 3500 and > 1000 individuals, respectively).
Positive matrix factorization was applied to the organic aerosol (OA) fraction to identify potential
contributions to the mass composition. Methanesulfonic-acid contributed 25%, sea salt organic
fragments 7 % and marine oxygenated, i.e. aged, OA 40 %. Local pollution from the generator was
responsible for 8 % and excluded from further analysis. An additional contribution of 18 % could be
attributed to amino acid and amine (AA) fragments originating most likely from activities at a nearby
penguin colony, supported by laboratory experiments. This unexpected contribution of biological
components to the aerosol with a high N:C ratio of 0.13 might have influence on the local nitrogen
cycle as particles get transported over longer distances before deposition than gas phase species. In
addition, these AA containing particles might have implications for cloud formation as biological
particles are known to be good ice condensation nuclei.
Page | 251
B3.1b - General dynamics
09.07.2013 13:15-14:45, Wisshorn
381
The Balanced Stream Function: decomposing of the mean meridional
circulation into eddy and diabatic-heating driven components in reanalysis
data
1
2
Ori Adam , Nili Harnik
1
2
ETH Zurich, Zurich, Switzerland, Tel Aviv University, Tel Aviv, Israel
The mean meridional circulation is represented using a linear operator of the mass stream function in
isobaric coordinates. The linear operator enables decomposing the total stream function into
components driven by Eddy momentum and heat fluxes, and diabatic heating. The various stream
function components are calculated and compared for the NCEP-NCAR, ERA-Interim and MERRA
daily reanalysis data. Self Organizing Map analysis of the stream function components is shown to
elucidate the variance among reanalyses and isolate the components contributing to observed trends
in the tropical and extratropical circulation.
Page | 252
701
The relations between jet stream, Hadely circulation, and eddy life cycle
transitons in an idealized model of the global circulation
1
2
Nili Harnik , Orli Lachmy
1
2
Tel Aviv university, Tel Aviv, Israel, Tel Aviv University, Tel Aviv, Israel
In its idealized form, the global circulation is a complex interaction between three components - the
Hadley cell, midlatitude jet streams, and storms. This three-way interaction gives rise to multiple
dynamical regimes, both for the Hadely circulation and the midlatitude jet streams. Model and
observational studies have shown several kinds of dynamical regimes and transitions, related to each
of these componenets, and to different flow characteristics. For example, there are thermally or eddy
driven jets, a single or double jet, subtropical or polar jets, an angular-momentum-conserving vs eddy
driven Hadely cell, and cyclonic and anti-cyclonic eddy life cycles. With the aim of bridging the gap
between idealized models of one or two of these componenets, and idealized GCM studies, we modify
a 2-level spherical quasi-geostrophic model to include the Hadely circulation by adding the agestrophic
advection terms in the zonal mean componenet. This yields maybe the simplest model which explicitly
resolves the main dynamical features of the Hadley circulation and midlatitude wave-mean flow
interactions.
We use this model to systematically examine the dominant blances behind These different dynamical
regimes, and how the dynamical transitions associated with each of the three componenets relate to
each other, and show how they relate to observed features of the circulation.
Page | 253
849
A proposal for representing large-scale processes in cloud simulations
1
2,3
2
4
Tapio Schneider , Zhihong Tan , Kyle Pressel , Joao Teixeira
1
2
Geosciences, ETH Zurich, Zurich, Switzerland, California Institute of Technology, Pasadena, United
3
4
States, ETH Zurich, Zurich, Switzerland, Jet Propulsion Laboratory, California Institute of
Technology, Pasadena, United States
Large-eddy simulations and other cloud-resolving simulations can only be expected to deliver
climatically relevant answers to the question of how clouds change with climate to the extent that the
large-scale processes driving such simulations are represented in a physically realistic manner. In
particular, this means that for simulations of clouds in statistically steady states, it is desirable that the
large-scale processes satisfy steady-state energy and moisture balances. The surface energy
balance, for example, is crucial for how the near-surface relative humidity responds to climate
changes; it is generally not satisfied in simulations that, as is commonly done, prescribe surface
temperatures and/or surface fluxes. Here we present a framework for forcing simulations of lowlatitude clouds with large-scale processes that respect such large-scale balances. Radiative energy
fluxes are modeled explicitly, albeit in an idealized manner, surface and top-of-atmosphere energy
balances are satisfied in climatically relevant ways, and large-scale eddy fluxes of sensible heat and
moisture are represented parametrically. We argue that such a representation of large-scale
processes is necessary to obtain realistic responses of clouds to climate changes and show
preliminary results of large-eddy simulations of subtropical low clouds.
Page | 254
1063
Statistical equilibrium LES with time varying forcing and the response of
subtropical low clouds to variations in climate
1
1,2
3
1
3
Kyle Pressel , Tapio Schneider , Joao Teixeira , Zhihong Tan , Georgios Matheou
1
2
3
California Institute of Technology, Pasadena, United States, ETH Zürich, Zurich, Switzerland, Jet
Propulsion Laboratory, California Institute of Technology, Pasadena, United States
Statistically steady state large eddy simulations (LES) will serve an increasingly important role in
understanding the representation of cloud processes and feedbacks in climate models. Therefore, it is
important to understand the characteristics of LES when in a statistically steady state. We will present
results of an analysis of spatial statistics of LES forced by an idealized climate model in a statistically
steady state. We will describe the effects of time varying statistically steady state large scale forcing
on the spatial statistics of dynamically relevant LES variables, and interpret these results in the context
of the design of LES experiments to inform parameterization development. Furthermore, statistically
steady state LES experiments will be used to address fundamental questions regarding the response
of subtropical low clouds to variations in climate.
Page | 255
A3.2b - Ocean’s role in climate variability, change, and predictability
09.07.2013 13:15-14:45, Schwarzhorn
272
Internal Southern Ocean centennial variability: dynamics, impacts and
implications for global warming
1,2
3
1
1
Mojib Latif , Torge Martin , Wonsun Park , Mohammad H. Bordbar
1
2
GEOMAR Helmholtz Center for Ocean Research, Kiel, Germany, Kiel University, Kiel, Germany,
3
MIT, Cambridge, MA, United States
It is well established that centennial climate variability can be externally forced by quasi-oscillatory
fluctuations of the solar constant or slowly varying atmospheric aerosol concentrations in association
with changes of volcanic activity. Climate models recently suggested that formidable centennial
variability can be also produced internally, and different competing mechanisms were proposed. This
paper deals with the internal Southern Ocean Sector centennial variability simulated by the Kiel
Climate Model (KCM). The centennial variability is linked to Weddell Sea deep convection and drives
not only regional but also global climate variations, as witnessed by coherent changes in Antarctic sea
ice and global average surface air temperature (SAT), respectively. Another important impact
concerns the Atlantic Meridional Overturning Circulation (AMOC). In particular, the AMOC strengthens
after the cease of Weddell Sea deep convection and Antarctic Deep Water (AABW) formation with a
time delay of several decades to a century. Finally, sea level variations associated with the Southern
Ocean centennial variability can be as large as ±20cm/century across the Antarctic Circumpolar
Current (ACC) and ±10cm/century in selected regions of the North Atlantic, which is of the same order
th
of magnitude as the rise of global average sea level during the 20 century amounting to about 1520cm.
Page | 256
760
Atlantic Meridional Overturning Circulation (AMOC) and climate
1
Rong Zhang
1
NOAA/GFDL, Princeton, United States
Changes in the Atlantic Meridional Overturning Circulation (AMOC) could have a profound impact on
global scale climate, as indicated by both observations and climate model simulations. This talk
highlights the global and regional scale climate impacts of the AMOC on paleo and modern climate, as
well as the current understanding of the linkage between AMOC variability and North Atlantic SST
(NASST) variability, both from a diagnostic and mechanistic viewpoint. In particular, the multidecadal
variations of NASST during the 20th century have highly debated origins, i.e. some suggested that
they are primly driven by changes in aerosols. In depth analyses show that there are important
discrepancies between modeled aerosol-forced response and observations, casting considerable
doubt on claiming aerosols as a prime driver for the observed multidecadal variations of NASST.
Independent fingerprints of AMOC variability show that the observed NASST variability is linked to
AMOC variations rather than merely a 20th century artifact of changes in radiative forcing. The talk will
also discuss the simulated climate impacts of the Nordic Sea overflow (the deep branch of the AMOC)
using a High Resolution Global Coupled Climate Model.
Page | 257
1011
The role of ocean-atmosphere interactions in the variability of the North
Atlantic summer storm track
1
1
2
3
Rowan Sutton , Buwen Dong , Tim Woollings , Kevin Hodges
1
Department of Meteorology, University of Reading, National Centre for Atmospheric Science,
2
Reading, United Kingdom, Department of Meteorology, University of Reading, Reading, United
3
Kingdom, Department of Meteorology, University of Reading, National Centre for Earth Observation,
Reading, United Kingdom
European climate exhibits variability on a wide range of timescales. Understanding the nature and
drivers of this variability is an essential step in developing robust climate predictions and risk
assessments. The North Atlantic storm track exerts a major influence on European climate. Its
variability in winter has been widely studied, but less attention has been paid to its variability in
summer. In this study we have investigated the variability of the North Atlantic summer storm track
using storm tracking and other diagnostics. We identify a dominant mode of variability characterised
by a meridional shift between two distinct storm paths, and diagnose the relationship to atmospheric
blocking and the role of two-way ocean-atmosphere interactions in this variability. We will present
evidence that, especially on multidecadal timescales, the Atlantic Ocean exerts an active influence on
the summer storm track, and that the rapid warming of the North Atlantic in the 1990s contributed to a
significant shift in European climate, towards a pattern characterized by anomalously wet summers in
northern Europe, and hot, dry, summers in southern Europe (with related shifts in spring and autumn).
In addition, there is evidence that ocean-atmosphere interactions within the summer season might
provide a positive feedback on storm track variability. We are carrying out model experiments to
understand more fully the mechanisms via which changes in the North Atlantic Ocean influence the
North Atlantic Storm track, and will report on the latest results.
Page | 258
775
Multi-scale oscillation of the climate changes in Central Asian form observation
to proxy data
1
2
Xingang Dai , Yijiang Yuan
1
2
RCE-TEA, Institute of Atmospheric Physics, CAS, Beijing, China, Institue of Desert Meteorology,
Urumqi, China
This study aims at investigating the climate change from inter-annual to multi-decadal scales in
northwestern China and Central Asia. Central Asia is far away from the ocean and has a very dry
inland-climate. Observation shows that the seasonal distribution of the precipitation in the region is
different from either the northwestern China or the Europe, but of a little bit similarity with the
Mediterranean Climate due to its special geography. The decomposition analysis of the precipitation
observations with orthogonal wavelet basis reveals that the climate has experienced a series of
changes in the two regions, characterized as a warming trend and mutli-decadal oscillations in
precipitation. A further analysis explored the phase relationship of the climate changes in connection
with AO or NAO, AMO and PDO. Besides, two longer sequences in precipitation reconstructed from
the tree rings shows that there exists a slower evolution of the precipitation on centurial scales in
northwestern China, which presents a chance to look inside into the relationship between the
observed precipitation trend in twenty century with global warming and the natural variation on longer
time scales than decades.
Page | 259
B1.1c - Advanced methods in data assimilation and ensemble forecasting
09.07.2013 13:15-14:45, Seehorn
956
Ensembles: why? And how?
1
Roberto Buizza
1
Research, ECMWF, Reading, United Kingdom
One of the main advances in numerical weather prediction of the past 20 years has been the
development and operational implementation of ensemble-based approaches in analysis and
forecasting. They provide more complete information than single analysis/forecast of the actual and
future state of the atmosphere, since they include an estimate of the uncertainty of the analysis and
the forecast states. At ECMWF, this has been achieved by building four key components in the
Integrated Forecasting System. At initial time, the high-resolution 4-dimensional variational
assimilation (4DV) and the lower-resolution Ensemble of Data Assimilations (EDA) provide an
estimate of the most likely initial state and its uncertainty. In forecast mode, the high-resolution
forecast (HRES) and the ensemble of lower resolution forecasts (ENS) provide an estimate of the
most likely future states and their uncertainties. In this talk, the current status of 4DV, EDA, HRES and
ENS and our plans to further develop them will be presented.
Page | 260
1155
Towards an adaptive multiscale ensemble system for convection forecasts
with stochastic parameterisations
1
1
1
Kirstin Kober , George C. Craig , Tobias Selz , Annette Förster
1
Ludwig-Maximilians-Universität München, München, Germany
1
A multiscale ensemble forecasting system enables to examine the relation between the predictability
of high impact weather and uncertainty coming from both small and large scales. Within the project
Pandowae (Predictability ANd Dynamics Of Weather Systems in the Atlantic-European Sector) such a
multiscale ensemble system is under development focusing on variability caused by convection.
The large scale variability is provided by a selection of 10 members of the global IFS ensemble
prediction system (EPS) of ECMWF. Within each of these 10 members, ten COSMO (Consortium for
Small-scale Modeling) model runs with 7 km horizontal resolution are nested. The 100 high resolution
forecasts use the the Plant-Craig stochastic convection parameterization representing convective
variability.
The skill of this existing part of the ensemble system (100 members) is investigated and compared
with observations with focus on precipitation forecasts. Neighbourhood verification techniques are
applied to compare the skill of the stochastic realizations with the standard Tiedtke convection
scheme. First results show that for high thresholds the forecasts with the Plant-Craig scheme are
superior to the Tiedtke forecasts. The probabilistic skill of the ensemble is also investigated.
The last component of the multiscale EPS representing small scale variability is currently under
development. COSMO experiments with 2.8 km horizontal resolution are nested into the 100 7 km
members with perturbations to the convective boundary layer. The amplitude of the variability is
determined based on physical processes affecting the initiation of convection in the boundary layer
like surface heating, subgrid scale orography or cold pools. Perturbations based on these processes
are added to the tendencies and analysed.
Page | 261
925
Self breeding: a new approach to estimate uncertainty strucutres in meso-scale
NWP models
1
Jan Keller
1
Hans-Ertel-Centre for Weather Research, Climate Monitoring Branch, Bonn, Germany
The estimation of fast growing error modes of the system is a key interest of ensemble data
assimilation when assessing uncertainty in initial conditions. Over the last two decades three methods
(and variations of these methods) have evolved for global numerical weather prediction models:
ensemble Kalman filter, singular vectors and breeding of growing modes (or now ensemble transform).
While the former incorporates a priori model error information and observation error estimates to
determine ensemble initial conditions, the latter two techniques directly address the error structures
associated with Lyapunov vectors. However, in global models these structures are mainly associated
with global wave patterns.
When using mesoscale limited area models, these perturbations structures are therefore often
included using perturbed boundary conditions while the initial perturbations (when used) are often
generated with a variant of an ensemble Kalman filter which does not necessarily focus on large scale
error patterns.
In the framework of the European regional reanalysis project of the Hans-Ertel-Center for Weather
Research, we use a mesoscale model with an implemented nudging data assimilation scheme which
does not support ensemble data assimilation. In preparation of an ensemble-based regional reanalysis
and for the estimation of three-dimensional atmospheric covariance structure we implemented a new
method for the assessment of fast growing error modes for mesoscale limited area models: The socalled self-breeding is new development based on the breeding of growing modes technique. Initial
perturbations are integrated forward for a short time period and then rescaled and added to the initial
state again. Iterating this rapid breeding cycle provides estimates for the initial uncertainty structure (or
local Lyapunov vectors) given a specific norm. To avoid that all ensemble perturbations converge
towards the leading Lyapunov vector we apply an ensemble transform variant to orthogonalize the
perturbations in the sub-space spanned by the ensemble.
Page | 262
1046
On the solution of the inverse tracer transport on the sphere
1
Janusz Pudykiewicz
1
Environment Canada, Dorval, Canada
The solution of the inverse problems for atmospheric tracers is of great importance for identifying of
unknown sources of chemical and nuclear materials emitted into the atmosphere. Very rapid
developments of new techniques in the past decade led to creation of promising methods based on
probabilistic and deterministic principles. Despite very different philosophical backgrounds of both
approaches, they share a common characteristic which is their reliance on the accurate solution of the
adjoint tracer transport equation. The main objective of this presentation is to discuss a non-oscillatory
and very efficient finite volume technique for solving of the tracer transport problem and its adjoint. The
proposed method is implemented on a hexagonal grid offering quasi-uniform resolution over the entire
sphere. The novel property of the algorithm is the use of the exponential propagation time stepping
which solves the linear advection problem exactly without practically any restriction of the time step
length. The proposed solver will be tested on a global scale in the framework of the deterministic
optimization system with preconditioning based on the analysis of the influence functions obtained
from the solution of the adjoint problem with different combinations of receptors. Important aspects of
the implementation of the method such as the selection of the wet scavenging and dry deposition of
tracers will be discussed as well.
Page | 263
594
Hidden error variance theory and its use in hybrid data assimilation
1
2
3
4
5
Craig Bishop , Elizabeth A. Satterfield , Kevin T. Shanley , David D. Kuhl , Tom Rosmond
1
2
Marine Meteorology Division, Naval Research Laboratory, Monterey, United States, Naval Research
3
4
Laboratory, Monterey, United States, Clarkson University, Potsdam, United States, Naval Research
5
Laboratory, Washington, United States, SAIC, Forks, United States
A conundrum of predictability research is that while the prediction of flow dependent error distributions
is one of its main foci, chaos fundamentally hides flow dependent forecast error distributions from
empirical observation. Empirical estimation of such error distributions requires that one obtain a large
sample of error realizations given the same flow and the same observational network. However,
chaotic elements of the flow and the observing network make it practically impossible to observe and
collect the conditioned sample of errors required to empirically define such distributions and their
variance. These variances are “hidden”. Here, an exposition of the problem is developed from an
ensemble Kalman filter data assimilation system applied to a 10 variable non-linear chaotic model and
25,000 replicate models. The output from this system motivates a new analytical model for the
distribution of true error variances given an imperfect ensemble variance. This model is defined by 6
parameters that also determine the optimal weights for the static and flow dependent parts of Hybrid
error variance models. Six new equations enable these hidden parameters to be accurately estimated
from a long time series of (innovation, ensemble variance) data pairs. This new-found ability to
estimate hidden parameters provides new tools for assessing the quality of ensemble forecasts, tuning
Hybrid error variance models and for post-processing ensemble forecasts. Preliminary results from
attempts to use the theory to speed the tuning of Hybrid data assimilation schemes will also be
presented.
Page | 264
B7.2a - Atmosphere Land Cryosphere Interactions
09.07.2013 13:15-14:45, Sertig
1194
A decade of carbon monoxide measurements: trends and shifts
1
2
3
3
3
3
James Drummond , Florian Nichitiu , Helen Worden , Merritt Deeter , David Edwards , John Gille ,
2
Jason Zou
1
2
Physics and Atmospheric Science, Dalhousie University, Halifax, Canada, Physics, University of
3
Toronto, Toronto, Canada, National Center For Atmospheric Research (NCAR), Boulder, United
States
On 18th December 1999 the Terra platform was launched carrying the Measurements Of Pollution In
The Troposphere (MOPITT) instrument. MOPITT has now completed over thirteen years of operation
measuring carbon monoxide (CO) over the planet.
The instrument stability has been outstanding and, despite a few anomalies over the mission, MOPITT
has been operating almost continuously since launch. Thirteen years (and counting) is over twice the
design life of the system and this has provided the longest continuous record of global CO available.
This record allows the identification of trends in global CO if the instrumental effects can be isolated.
Long-term variations in global CO have been identified in the MOPITT data that are not attributable to
the instrument, appear to be atmospheric in origin and are also seen to a greater or lesser extent in
other global CO time series (Worden et al., ACP, 13, 837-850, 2013). A more thorough analysis is
being undertaken to quantify these changes and to further validate them by comparison with other
available data. There is evidence of a downward “shift” in the amount of CO over the globe around
2008 and a possible overall downward trend during the first decade of this century. This presentation
will focus on our understanding of these trends both from an instrumental point of view - are they real?
- and from an atmospheric point of view - why are they happening?
MOPITT was provided to the Terra spacecraft by the Canadian Space Agency and was built by
COMDEV of Cambridge, Ontario. Data processing is performed by the MOPITT team at the National
Center for Atmospheric Research, Boulder, CO. Instrument control is by the team at the University of
Toronto.
Page | 265
689
Past and future changes of organic and inorganic nitrogen global atmospheric
deposition
1
2
2
3
Maria Kanakidou , Nikolaos Daskalakis , Stylianos Myriokefalitakis , Konstantinos Tsigaridis
1
2
3
University of Crete, Heraklion, Greece, Chemistry, University of Crete, Heraklion, Greece, Center
for Climate Systems Research, Columbia University, and NASA Goddard Institute for Space Studies,
New York, United States
Nitrogen is important nutrient that controls the productivity of terrestrial and marine ecosystems.
Emissions of reactive nitrogen into the atmosphere are increasing due to human activities, affecting
also nitrogen deposition to the surface. There is also growing evidence that a significant fraction of
nitrogen deposition occurs in the form of organic nitrogen, although the chemical characterization of
this fraction remains a challenge.
The present study uses a global chemistry transport model (TM4-ECPL) to calculate the global
distribution of nitrogen deposition - accounting for both its inorganic and organic fractions in gaseous
and particulate phases. TM4-ECPL accounts for all major aerosol components, for oxidants and
volatile organic chemistry and for secondary organic aerosol formation. The global distributions of
organic and inorganic fractions of nitrogen deposition are computed and evaluated against recent
observations.
Present-day simulations suggest that the global organic nitrogen cycle has a strong anthropogenic
component with ~45% of the overall atmospheric source (primary and secondary) associated with
anthropogenic activities. Total present-day nitrogen deposition amounts about 122 Tg-N/yr globally
from which about 58% is deposited over land. Organic nitrogen carried by particles is estimated to
contribute by 70% to the global atmospheric soluble organic nitrogen deposition that is estimated to be
about 32Tg-N/yr with an order of magnitude of uncertainty. Significant past and future changes in
these depositions due to human activities are also evaluated by TM4-ECPL driven by changes in the
emissions of nitrogen deposition precursors.
Page | 266
1119
Observations of the dry column of carbon dioxide and methane from
instrumentation on space based and airborne borne platforms
1
1
1
1
1
John Burrows , Henrich Bovensmann , Michael Buchwitz , Maximillian Reuter , Oliver Schneising ,
1
1
Thomas Krings , Konstantin Gerilowski
1
Institute of Environmental Physics, University of Bremen, Bremen, Germany
Carbon dioxide, CO2, and methane, CH4, are the two most important greenhouse gases.
Anthropogenic emissions have been increasing rapidly since the beginning of the industrial revolution
and the birth of the anthropocene. Global measurements of both the dry columns of CO2 and CH4
have been demonstrated column from space by SCIAMCHY (SCanning imaging Absorption
spectrometer for Atmospheric CHartography) and also GOSAT Tanso. The aircraft borne MaMap
measurements have shown that point sources and their emissions can be readily identified using high
spatial resolution measurements. The CarbonSat and Carbonsat constellation will when flown provide
global measurements, suitable for the long term monitoring of CO2 and CH4 form space. The results
form SCIAMACHY and MaMap will be discussed and the potential for CarbonSat and SCIA-ISS
instrument on the International Space Station will be discussed.
Page | 267
984
Observation of CH4 at high latitudes from space by the French-German climate
mission MERLIN
1
2
Gerhard Ehret , Pierre H. Flamant
1
2
Institut für Physik der Atmosphäre, DLR, Wessling, Germany, École Polytechnique, Laboratoire de
Météorologie Dynamique, Palaiseau, France
CH4 emissions and sinks are tightly coupled to the global climate system and the water cycle. A global
warming in Arctic regions might foster the melting of permafrost soils which contain significant
amounts of carbon in organic form which under anaerobic conditions might be converted to CH4 and
partially released to the atmosphere. Large seasonal variations of methane concentrations are
expected between 60N and 70N. There exist also very large deposits of CH4 as hydrates on ocean
shelves that are vulnerable to ocean warming. Paleo records indicate that both processes can have
important feedbacks in the climate system. For reducing uncertainties on the global methane budget
and climate feedback, monitoring of atmospheric CH4 at high latitudes is therefore of paramount
interest. We report on the mission MERLIN which is the French-German climate monitoring initiative
on global observations of atmospheric methane (CH4). As a novel feature, the space instrument of this
small satellite mission will be based on a pulsed lidar system for the measurement of spatial and
temporal gradients of atmospheric CH4 columns along the satellite sub-track. The lidar instrument
permits all-season and all-latitude coverage as it is not relying on sunlight. Initial impact studies clearly
indicate substantial reduction of the prior methane flux uncertainties in key observational regions when
using synthetic MERLIN observations in the flux inversion experiments. Together with the data from
current and forthcoming observational network and appropriate modelling and interpretative activities,
MERLIN observations will allow to constrain further development of models of the terrestrial biosphere
thus improve the projections of future trends in carbon sources and sinks particularly at high latitudes.
Page | 268
659
The role of the stable winter Arctic boundary layer in enhancing Arctic
amplification
1
1
1
Glen Lesins , James Drummond , Thomas Duck
1
Dept of Physics and Atmospheric Science, Dalhousie University, Halifax, Canada
The winter Arctic boundary layer typically possesses high static stability which suppresses turbulent
fluxes and isolates the layer from the free troposphere. This acts to restrict the influence of surface
forcing anomalies to a layer close to the surface resulting in an amplification of the surface air
temperature response. The enhancement of the magnitude of the Arctic amplification due to boundary
layer stability acts on the response from forcings such as enhanced meridional transport and sea ice
loss that are typically cited as the cause of the amplification.
Here we present evidence of the role of the stable winter Arctic boundary layer in magnifying Arctic
amplification by analyzing radiosonde profiles from 22 Canadian stations extending from 1971 to
2010. The Amplification factor varies from 1.4 to 5.2 depending primarily on the station's latitude. The
surface energy balance (SEB) equation is used to relate the response of the surface temperature to
changes in the surface energy fluxes. Based on the SEB analysis, there are four factors that contribute
to Arctic amplification: 1) a larger change in net downward radiation at the Arctic surface compared to
the global average, 2) a larger below surface conductive heat flux change than the global average, 3)
weaker sensible and latent heat flux responses and 4) a colder skin temperature compared to the
global average, which forces a larger surface warming to achieve the same increase in upward
longwave radiation. The observed correlations between the warming trends and both the inversion
strength and the surface air temperature are shown to be consistent with the SEB analysis.
Page | 269
C4.1c - Meteorological forcing data and distributed modelling of snow, ice and
hydrology in mountain watersheds
09.07.2013 13:15-14:45, Sanada I
886
Modelling of the spatial variability of the snow cover and the runoff of
glacierized catchments
1,2
1
1,3
4
2
Johannes Schöber , Katrin Schneider , Kay Helfricht , Stefan Achleitner , Fritz Schöberl , Robert
5
Kirnbauer
1
2
alpS Centre for Climate Change Adaptation Technologies, Innsbruck, Austria, Institute of
3
Geography, University of Innsbruck, Innsbruck, Austria, Institute of Meteorology and Geophysics,
4
University of Innsbruck, Innsbruck, Austria, Unit of Hydraulic Engineering, University of Innsbruck,
5
Innsbruck, Austria, Institute for Hydraulic and Water Resources Engineering, Vienna University of
Technology, Vienna, Austria
In this study airborne laser scanning (ALS) snow data from the end of winter is used for the calibration
and validation of the snow-hydrological model SES for glacierized catchments with different areas
between 25 and 170 km² in Tyrol, Austria. A simple regression model is used to convert the basinwide ALS data into SWE whereby the snow course data on which the statistical model is based agrees
with the ALS data in terms of the spatial variability over different elevation zones. Despite its simplicity
this regression approach keeps the observed spatial variability of the snow cover.
The fully distributed energy balance based model SES is used to simulate the accumulation and
ablation of the snow cover as well as the catchment runoff. A geostatistical analysis of the ALS data
shows that the glacierized areas have a spatial variability of about one order of magnitude lower than
the non-glacierized catchment parts. Scale breaks which indicate the degree of correlation between
ALS data points vary between 25 and more than 100 m and give guidance for an appropriate model
resolution. Based on the ALS data and on additional optical satellite data typical snow accumulation
patterns are derived. On the hillslope scale slope and curvature are used to redistribute the simulated
SWE in the SES-model.
Comparing the observed and simulated snow on various dates the simulated snow covered area
(SCA) shows a high accordance whereas for SWE errors are relatively higher. Nevertheless, for the
simulation of the snow accumulation the inclusion of the basin-wide SWE helps to apply an
appropriate input precipitation and to considerably reduce the parameter uncertainty of the SESmodel. For the runoff modelling the assimilation of the basin-wide SWE data allows to quantify the
sensitivity of the spatial distribution of snow on the catchment's discharge and the according
parameters.
Page | 270
888
Accounting for small-scale snow variability to enhance snow water resource
monitoring
1
1
1
Tobias Jonas , Jan Magnusson , Nora Helbig
1
WSL / SLF, Davos, Switzerland
Understanding spatial patterns in snow accumulation, redistribution and melt is crucial in alpine snow
hydrology. Monitoring snow water resources is needed for lake and reservoir management as well as
for forecasting of snow-melt related spring floods. In Switzerland, while dense networks for daily snow
measurements exist, they do not resolve the spatial variability of snow at scales that are important for
snowmelt modelling. Distributed snow hydrological models on the other hand are often constrained by
the ability to provide them with accurate meteorological forcing fields.
In this study we focus on a conceptual snow distribution model primarily driven by snow data from
monitoring networks. While this model is aimed at large-scale operational snow water resources
monitoring, its performance is assessed using field data that resolves the fine-scale natural variability
2
of snow depth and density from a 50 km test catchment.
We use operational monitoring network data as direct model input and represent small-scale variability
at a subgrid level based on high resolution snow distribution data from experimental remote sensing
datasets. The analysis shows that the model performance is substantially increased after including a
subgrid representation of small-scale variability. Such an approach may also be applicable for other
meteorological variables that show complex spatial distribution.
Page | 271
809
Towards assimilation of snow depth and SWE observations in multi-layer
detailed snowpack models
1
2
3
1
1
Samuel Morin , Richard Essery , Ghislain Picard , Matthieu Lafaysse , Marie Dumont , Fatima
1
Karbou
1
2
Météo-France - CNRS, CNRM - GAME, CEN, St Martin d'Heres, France, University of Edinburgh,
3
Edinburgh, United Kingdom, CNRS - UJF Grenoble, LGGE, Grenoble, France
Due to errors in meteorological forcings (measured, analyzed or forecast), land surface model
themselves, and the fact that many small scale processes are often not explicitly accounted for in
snowpack models (wind drift effects, etc.), simulated snowpack properties often deviate from
observations, especially in mountainous terrain. In such a context, data assimilation is a promising tool
aiming at combining model results with observations to produce the best possible assessment of the
physical properties of snow on the ground. While data assimilation techniques are commonly used in
atmospheric and ocean models, the assimilation of land surface observations is still challenging in
many respects. Here we introduce a simplified extended Kalman filter (SEKF) approach to assimilate
point scale snow observation (depth or SWE) in the multi-layer detailed snowpack model Crocus,
coupled to the land surface scheme ISBA within the SURFEX interface. This approach was found to
be able to cope satisfyingly with the fact that Crocus handles a number of numerical snow layers
which varies in time, as well as the fact that snow on the ground is not always present. The results
indicate that the assimilation of snow depth observations is generally more powerful than assimilating
SWE, as long as a processes responsible for variations of the snow density (compaction, percolation,
phase change etc.) are sufficiently well represented in the model. Examples from the French Alps
using various meteorological forcings and ground snow observations will be described. Potential
extensions of the developed framework for the assimilation of remote sensing observations will be
discussed. This includes for example passive microwave data assimilation using a physically-based
observation operator using simulated snow properties as input.
Page | 272
1106
Fusion of coincident remote sensing, modeling, and ground based
observations for accurate spatial estimates of snow water equivalent
1
2
2
3
Hans Peter Marshall , Danny G. Marks , Adam H. Winstral , Rupesh Shrestha
1
2
Geosciences, Boise State University, Boise, United States, Northwest Watershed Research Center,
3
Agricultural Research Service, Boise, United States, Geosciences, Idaho State University, Boise,
United States
Quantifying the spatial distribution of snow water equivalent (SWE) over large spatial extents in the
mountains, at the necessary resolution to capture local variability, is not currently practical due to the
complexity of snow distribution.
Manual measurements are far too time consuming, high resolution physically based modeling is
computationally intensive and uncertainties in forcing data, which is typically large at small scales due
to sparse meteorological observations, propagate directly to the modeled SWE. High resolution
remote sensing techniques can have spatially variable uncertainties and infer SWE from indirect
observations.
We combine conincident information from airborne LiDAR, ground-based radar, computationally
efficient energy balance modeling, and in-situ observations to produce optimal SWE estimates, which
leverage the advantages of each technique. Quantitative comparisons using subsets of this rich
dataset are used to design efficient field observation strategies coincident with airborne LiDAR, guided
by model estimates, to develop strategies for combining these techniques at large scales, in locations
with limited prior information, for optimal estimation of high resolution SWE.
Page | 273
1123
Application of satellite-based surface radiative fluxes to improve snowmelt
modeling
1
2
3
4
4
4
Laura Hinkelman , Karl Lapo , Jessica Lundquist , Rachel Pinker , Yingtao Ma , Eric Nussbaumer
1
Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, United
2
3
States, Dept. of Atmospheric Sciences, University of Washington, Seattle, United States, Dept. of
4
Civil and Environmental Engineering, University of Washington, Seattle, United States, Dept.
Atmospheric and Oceanic Science, University of Maryland, College Park, United States
Snow processes are important to stream flow, surface water availability, groundwater recharge, and
other aspects of the water cycle. Models that accurately represent both the timing and spatial
distribution of snowmelt are essential for improving our understanding of both local and regional
hydrology. The greatest potential sources of error in simulating snowmelt rates and timing are
inaccurate solar and longwave irradiance inputs. Because ground-based irradiance measurements are
not widely available in mountainous areas, many hydrologic models estimate solar inputs from the
position of the sun and the local diurnal temperature range while longwave fluxes are estimated from
near-surface temperature and humidity. This can lead to errors of up to 50% in snowmelt rates.
Here we examine the benefit of using solar and longwave surface flux data from NASA satellites to
replace parameterizations commonly used in snow models. The satellite products employed are the
CERES SYN data set and a MODIS-based research data product. CERES SYN was selected
because it has relatively high temporal sampling (three-hourly), although its spatial resolution is only
1°. The MODIS data has lower temporal sampling (four times per 24-hour day) but higher spatial
resolution (5 km). Together, these products allow us to evaluate the relative importance of spatial and
temporal sampling.
This presentation highlights several results of this research. We first describe a study of the sensitivity
of snow models to perturbations in solar and longwave radiative inputs. This study indicates that bias
errors have a greater effect on modeled snow water equivalent (SWE) than random errors do. We
then illustrate the effect of spatial scale on the agreement between satellite-based and measured
irradiances in mountainous areas. Finally, we present comparisons between SWE modeled using
irradiances from the satellite products versus parameterizations and draw conclusions about the
usefulness of satellite data based on our results.
Page | 274
B4.1c - Global monsoon system: past, present and future
09.07.2013 13:15-14:45, Aspen I
277
The interdecadal variability of the East Asian summer monsoon around the
late-1990s and Its association with the Northern Hemisphere teleconnection
patterns
1
1
Ronghui Huang , Yong Liu
1
Institue of Atmospheric Physics, Beijing, China
The interdecadal variability of the East Asian summer monsoon (EASM) is analyzed by using the
observed precipitation data in China and the NCEP/NCAR reanalysis data. Results show that the
summer rainfall in eastern China experienced a significant interdecadal variability around the late1990s. Accompanying with the interdecadal variability of the EASM, the first leading mode of the
summer rainfall anomalies became from a meridional tripole pattern into a meridional dipole pattern,
which exhibited a characteristic of flood in South China and drought in North China. And the results
also show this interdecadal variability of the summer rainfall was closely associated with the
interdecadal variability of the summer monsoon circulation over East Asia.
The internal dynamical cause of this interdecadal variability of the EASM, especially the variation of
zonal-mean zonal wind and its influence on the teleconnection patterns in the upper/mid-troposphere
over Eurasian continent, is investigated. During 1999-2010, since the subtropical westerly jet
weakened and shifted poleward, the zonal-mean zonal wind anomalies over East Asia exhibited a
meridional dipole pattern. This led to significant interdecadal variations of three types of teleconnection
patterns over Eurasian continent, i.e., the “Silk Road” pattern, the “EU” pattern, and the East
Asia/Pacific (EAP) pattern, which resulted in water vapor transportation divergence and convergence
over the northern and southern regions of East Asia during 1999~2010.
The thermodynamical cause of the interdecadal variability of the EASM system is also discussed from
the variation of the temperature advection in the mid-troposphere over East Asia. During 1999-2010,
because of the interdecadal variation of teleconnection patterns over Eurasian continent, cold (warm)
advection in the northern (southern) region of East Asia induced the intensification of descending and
ascending flows in the northern and southern regions of East Asia, respectively. These caused the
occurrence of the interdecadal variability of EASM around the late-1990s.
Page | 275
270
The influence of tropical SST on out of phase decadal rainfall change in spring
and summer over South China
1
1
2
Jinhai He , Zhiwei Zhu , Tim Li
1
School of Atmospheric Sciences, Nanjing University of Information Science and Technology, Nanjing,
2
China, Department of Meteorology, University of Hawaii at Manoa, Honolulu, United States
A decadal circulation shift in mid-1990s of East Asian accompanying an out of phase rainfall change
over South China in spring and summer is detected by using different reanalysis data and observation
data for 1979-2010. During spring (March-May), the first principal component (PC) of the multivariate
empirical orthogonal function (MV-EOF) exhibits a decadal turning around mid-1990s, while in summer
(June-August) the second PC of the MV-EOF also shows a sharp decadal shift in mid-1990s. It is
found that the decadal turning of MV-EOF modes in spring and summer is accompanied by an out of
phase decadal rainfall altering over South China: from the pre-mid-90s epoch (1979-1992) to the
recent epoch (1997-2010), the rainfall reduces in spring and increases in summer, respectively.A
mechanism is put forward to explain the out of phase decadal rainfall change over South China in
spring and summer. In spring, the composite differences of SST between the two epochs indicate a La
Niña-like pattern with warming in west Pacific and cooling in eastern Pacific. This pattern, therefore,
enhances the Walker cell which then strengthens the local Hadley cell and causes a dipole pattern
with positive rainfall anomalies to the south of 20°N in East Asian and negative rainfall anomalies over
South China. While during summer, the cooling in eastern Pacific is dissipated and the La Niña-like
pattern is greatly weakened. In addition, the warming SST over Indian Ocean is greatly extended
southward and eastward. Hence, the Walker cell is depressed and simultaneously weakens the local
Hadley cell, and finally deepens the East Asian summer monsoon trough, leading positive rainfall
anomalies over South China.
Keywords: decadal shift in mid-1990s, the Walker cell, the Hadley cell, Indian Ocean warming, South
China precipitation.
Page | 276
371
Identifying oceanic origin of continental rainfall through integrated transport
1
1
W. Timothy Liu , Xiaosu Xie
1
Jet Propulsion Laboratory, Pasadena, United States
Over a decade of Tropical Rain Measuring Mission (TRMM) rainfall and spacebased observation of
integrated moisture transport (IMT) are used to characterize the ocean source of continental rainfall.
On the annual time scale, the dominant signal is the monsoon. The annual variations of rainfall in the
Amazon and La Plata river basins in South America are found to be in phase with the mass change
measured by Gravity Recovery and Climate Experiment GRACE, and the IMT across relevant
segments of the Pacific and Atlantic coasts. Over the Western Africa Monsoon region, our IMT data
combine onshore transport at surface with offshore transport aloft, and identify two rain regimes
controlled by moisture from two different oceans. Rainfall in the south is caused by moisture from the
Gulf of Guinea, which peaks in June. Rainfall in the north (Sahel) is driven by moisture from the
Atlantic in the west, which peaks in August. The IMT from the Arabian Sea across the simplified
coastline of the Indian subcontinent has high correlation with TRMM rainfall over most of India. The
exception is in the Tamil Nadu region in the southeastern part of the subcontinent; the annual rainfall
variation here is found to be complicated by moisture transport from the Bay of Bengal through the
winter monsoon as well as tropical jet from the warm pool over the South China Sea.. The dominant
influence of IMT from the Bay of Bengal and South China Sea over those from the Western Pacific is
evident in the rainfall in China. During the past decade, there are several El Nino/Southern Oscillation
episodes that dominate the inter-annual anomalies and our analysis reveals how the transport is
related to rainfall anomalies. The rain and transport relation at short time scales, including the landfall
of tropical cyclones, is being explored.
Page | 277
120
The time-lagged impacts of spring sensible heat over the Tibetan Plateau on
the summer rainfall anomaly in East China
1
1
1
Anmin Duan , Ziqian Wang , Guoxiong Wu
1
State Key Laboratory of Numerical Modelling for Atmospheric Sciences and Geophysical Fluid
Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
This study explores the time-lagged impacts of the spring sensible heat (SH) source over the Tibetan
Plateau (TP) on summer rainfall anomaly in east China by using the WRF model. Numerical
experiments for the 2003 case indicates that spring SH anomaly over the TP can maintains its impact
until summer and leads to the overall strong atmospheric heat source, which is characterized by the
enhanced both SH over the western TP and condensation latent heat to the east. The wave activity
diagnosis revealed that the enhanced TP heating forces a Rossby wave train to the downstream
regions. The cyclonic response to the northeast TP brings about the low level northerly anomaly over
the northern China, while the anticyclonic response over the western Pacific enhances the subtropical
high and the low level southerly in its western flank. As a result, cold and dry airflows from mid-high
latitudes and warm and wet airflows from tropical oceans converge around the Huaihe River basin. In
addition, warm advection originated from the TP induces vigorous ascending motion over the
convergence belt. With such a favourable circulation condition, the eastward propagating vortexes
initiated over the TP intensify the torrential rainfall processes over the Huaihe River basin. Another
case study of 2001 with weak spring SH over the TP and the overall southward retreat of summer
rainfall belt in east China further demonstrates the role of spring SH over the TP in regulating the
interannual variability of EASM in terms of wave activity and synoptic disturbance.
Page | 278
56
Modulation of the Tibetan Plateau snow cover on the ENSO teleconnections:
from the East Asian summer monsoon perspective
1
2
Zhiwei Wu , Jianping Li
1
2
Nanjing University of Information Science and Technology, Nanjing, China, Institute of Atmospheric
Physics, Chinese Academy of Sciences, Beijing, China
The East Asian summer monsoon (EASM) may exhibit rather large variability between years
characterized by the same ENSO phase. Such inconsistency reduces the EASM predictability based
on ENSO. Results in this study show that the Tibetan Plateau snow cover (TPSC) exerts a modulating
effect on ENSO teleconnections and ENSO significantly correlates with the EASM only during the
reduced TPSC summers. Three-dimensional circulation structures are examined to manifest that the
typical ENSO signals in reduced TPSC summers tend to be stronger than in excessive TPSC
summers. Numerical and theoretical evidences indicate that the anomalously reduced TPSC can force
positive geopotential height anomalies at the upper troposphere and weaken the jet streams across
eastern Asia and northwestern Pacific. Governed by such basic state zonal flows, the extratropical
Rossby wave response to the ENSO forcing usually has a larger amplitude and pronounced westward
development. In such case, ENSO extends its influences to the eastern Asia and enhances its
connection with the EASM.
Page | 279
A4.2d - Sea ice and Ocean-Atmosphere Interactions
09.07.2013 16:15-17:45, Sanada II
1120
Evaluating Arctic sea ice cover in the CMIP5 model ensemble
1
1
Andrew Barrett , Julienne Stroeve , Mark Serreze
1
University of Colorado, Boulder, United States
1
We evaluate simulations of late 20th and early 21st century sea ice cover for global climate models
participating in the World Climate Research program Coupled Model Inter-comparison Project Phase 5
(CMIP5) using sea ice extent and thickness products derived from satellite, airborne, submarine and
in-situ data. Although all of the models show declining ice extent in the period of observations, trends
from most of these are smaller than observed. The ability of models to capture the observed variability
depends in part on how well they are able to simulate the observed ice thickness distribution. Models
with overly thick sea ice tend to lose sea ice cover later than models with thinner ice. While long-term
basin-wide sea ice thickness data are not available for the Arctic, a combination of satellite data from
ERS1/2, ICESat and Cryosat, together with sea ice thicknesses derived from NASA´s operation
IceBridge, provide a record of the evolution of ice cover from the early 1990´s to present. Submarine
sonar data are used to extent the record further back in time but coverage is more limited.
We use the combined records of satellite, airborne and submarine derived thickness data to evaluate
how well CMIP5 model capture the spatial distribution of mean winter ice thickness fields and how this
relates to the observed trends in sea ice extent. Model simulations of the Arctic Amplification are
examined in the context of model representation of sea ice thickness and extent.
Page | 280
794
Seasonal forecasts of the Arctic sea ice with a coupled atmosphere-ocean
global climate model
1,2
1
1
2
1
Matthieu Chevallier , David Salas y Mélia , Agathe Germe , Gilles Garric , Michel Déqué
1
2
CNRM-GAME, Météo-France, Toulouse, France, MERCATOR-OCEAN, Toulouse, France
Experimental seasonal forecasts of the Arctic sea ice cover have been performed with CNRM-CM5,
one of the CMIP5 global coupled climate model (roughly 1° horizontal resolution). Ensemble
predictions of March and September Arctic sea ice are initialized on November 1st and May 1st, every
year over the period 1990-2010. Initial states for ocean and sea ice are provided by a reconstruction
run with the oceanic component of CNRM-CM5 (NEMO3.2 coupled to Gelato5), forced by the ERAInterim reanalysis. In this ocean-sea ice reconstruction, the sea ice thickness regional distribution has
been carefully validated using the most recent data sets available now. Skill scores of the seasonal reforecasts of the pan-Arctic sea ice extent are very promising, even in the presence of model biases.
These experiments show that a large fraction of the September sea ice minimum is predictable as
early as in May. It confirms the role played by the initial sea ice volume and thickness distribution,
which has been suggested by earlier studies. The system produces also very encouraging forecasts of
the winter sea ice edge. Such forecasts of the March sea ice cover have not been much addressed in
the literature, and are more challenging due to the role played by coupled air-ice-sea processes. A
regional investigation of the winter forecasts helps precising the role played by the upper ocean in
shaping the ice cover in the marginal ice zones (especially in the Barents and the Bering sea), and
suggests some ways forward in the design of future global and regional sea ice forecasting systems.
Page | 281
647
The sea ice albedo effect: improving polar amplification in model simulations
of the mid-Pliocene
1
1
1
1
1
Fergus Howell , Alan Haywood , Jane Francis , Steven Pickering , Bridget Wade , Harry Dowsett
1
2
School of Earth and Environment, University of Leeds, Leeds, United Kingdom, US Geological
Survey, Reston, United States
2
Sea ice exerts a large influence over the climate in high latitudes in the Northern Hemisphere, so it is
crucial that general circulation models (GCMs) represent sea ice processes proficiently. One of the
most important processes related to sea ice is the albedo feedback. Recent studies of sea ice albedo
hint that the standard minimum albedo values used in GCMs could be too high. The minimum sea ice
albedo value in a GCM is often used as a tuning parameter, with the tuning typically for modern day
climate, which may not be appropriate for a climate substantially different to the present.
Climatological reconstructions of the mid-Pliocene warm period (3.29 - 2.97 Ma) indicate that global
mean temperatures were approximately 3°C higher than present day, with a warming of up to 10°C in
the Arctic and North Atlantic. However, GCM simulations of this time period have failed to reproduce
this high-latitude warming. An inappropriately high minimum sea ice albedo value could be preventing
higher levels of polar amplification. In a warmer than present climate such as the mid-Pliocene, it is
likely that a greater proportion of the ice in summer is first year ice, which has a lower average albedo
than multi-year ice.
To investigate the full effects of changes to maximum and minimum albedo values on mid-Pliocene
simulations, 24 different simulations with varying albedo settings were run using HadCM3. The same
simulations were also run with pre-industrial boundary conditions.
For simulations with reduced minimum albedo, mean annual surface air temperatures north of 70°N
show an average increase of 2-3°C, with up to 6°C increase in some areas. This suggests that
changes to the albedo in the models could make a contribution to achieving the polar amplification that
mid-Pliocene simulations currently fail to obtain.
Page | 282
827
Sensitivity of model simulated Arctic sea-ice to realistic ice thickness
distributions and snow parameterizations
1
1
1
1
1
Karel Castro Morales , Frank Kauker , Martin Losch , Kathrin Riemann-Campe , Stefan Hendricks ,
1
1
1
Cornelia Köberle , Michael Karcher , Rüdiger Gerdes
1
Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Bremerhaven, Germany
Sea-ice plays a key role in the Arctic Ocean. Based on simulations with a general circulation model of
the Arctic that is driven by realistic atmospheric forcing, we analyze the impact of changing two
parameterizations in the sea-ice model: 1) the ice probability density function (pdf) of ice thickness
classes that is used for the calculation of the surface heat budget, and 2) the description of the snow
layer. For the latter, we tested two different types of parameterization commonly used in sea-ice
models, a homogeneous distribution independent of the sea ice thickness underneath, and a
distribution proportional to the applied ice pdf. Our results show that prescribing ice thickness
distribution from 7 uniform categories to 15 non-uniform categories, obtained from various airborne
electromagnetic induction sounding measurements (EM-bird), and distributing the snow layer
according to the ice pdf, the average ice thickness increases by 55 cm during the simulated period of
1990 to 2007. It is found that this is a direct re sponse to the increase in the thermodynamic growth
3
during the months of ice formation, for example nearly 600 km per month for January. Our results
stress the importance of these parameterizations in sea-ice modelling and suggest that more field
observations of ice thickness and, even more importantly of snow depth, are needed to reduce the
uncertainty in model simulations and consequently of future projections of Arctic sea-ice.
Page | 283
1086
Impacts of climate change on fresh water content and sea surface height in the
Beaufort Sea
1
1
Will Perrie , Zhenxia Long
1
Bedford Institute of Oceanography, Dartmouth, Canada
The present study explores how fresh water content and sea surface height in the Beaufort Sea might
be modified under warming-induced conditions due to climate change. We performed simulations from
1970 to 2069 with a coupled ice-ocean model (CIOM) implemented for the Arctic Ocean. The surface
fields to drive CIOM were provided by the Canadian Regional Climate Model (CRCM), in turn driven
by the third-generation Canadian global climate model (CGCM3) outputs following the A1B climate
change scenario. The simulated sea ice concentration in the entire Arctic and the fresh water content
in the Beaufort Sea are shown to have consistent patterns as those seen in observations and
reanalysis data. In terms of the possible future climate, the CIOM simulations suggest an 11%
decrease per decade in ice volume, when the Arctic Ocean would become largely ice free in the
summers by about ~ 2069. Moreover, due to increases in melting of sea ice and Ekman transport,
there is an increasing trend in fresh water content (FWC) and sea surface height (SSH) in the Beaufort
Sea. The increase would be about 2.5 m for FWC and 6 cm for SSH from 1979 to 2069. Finally, the
simulations also suggest that maximum increases in the FWC and SSH would occur near the center of
the Beaufort Gyre, where the maximum FWC and SSH are located.
Page | 284
C6.2b - Avalanche formation and forecasting
09.07.2013 16:15-17:45, Aspen II
76
Influence of weak layer heterogeneity on snowpack stability
1
1
1
Gaume Johan , Chambon Guillaume , Eckert Nicolas , Naaim Mohamed
1
IRSTEA, Grenoble, France
1
The spatial variability of snow mechanical properties has an important impact on snowpack stability
and thus on avalanche formation. In this study, a mechanically--based statistical model of the slab-weak layer (w.l.) system relying on random finite element simulations is used to investigate snowpack
stability and avalanche release probability. This model accounts, in particular, for the spatial varibility
of w.l. mechanical properties and stress redistributions by elasticity of the slab. We show how
avalanche release probability can be computed from release depth distributions which allow us to
study the influence of w.l. heterogeneity, slab depth and slope angle on snowpack stability. Finally, the
importance of smoothing effects is verified and the crucial impact of heterogenity characteristics on the
so-called knock-down effect on slope stability is revisited using this model.
Page | 285
1245
Relating weak layer and slab properties to snow slope stability
1
1
1
Jürg Schweizer , Benjamin Reuter , Sascha Bellaire
1
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland
Snow slope stability evaluation requires considering weak layer as well as slab properties - and in
particular their interaction. The thickness and properties of the slab layers will strongly influence failure
initiation, but also crack propagation crucially depends on slab properties. Of course, initiation and
propagation is only possible with a weak layer prone to fail that offers a suitable crack path. We derive
snow properties from gridded snow-micropenetrometer measurements from 13 snow slopes. Microstructural as well as bulk properties of weak and slab layers were related to slope stability assessed
with compression tests and other observations of instability. Instead of applying a fully mechanical
approach that requires profile-specific finite element modeling, we aimed at a classification scheme so
that SMP resistance profiles can be classified in terms of stability into poor, fair and good.
Page | 286
853
Application of a simple snow cover model to avalanche warning systems
1
2
2
2
Kouichi Nishimura , Asami Komatsu , Kazuhiro Tanji , Naoki Matsuoka
1
2
Nagoya University, Nagoya, Japan, Japan Weather Association, Sapporo, Japan
Today, road administrators monitor surface avalanche risk by measuring snowfall. However, such a
method will not enable them to forecast an avalanche occurrence because there may be various
causal factors for an avalanche.
Our study proposes one simple snow cover model that can be applied to snow transformation. The
model can estimate snow temperatures and density from meteorological data including air
temperatures and snowfall (or rainfall). A stability index SI can be obtained by applying the shear
formulation and slope inclinations to the model. We have created an avalanche warning system that
issues SI forecast from Numerical Weather Prediction System (NWS) which is updated every hour.
The performance of this model has been verified by using the data of past avalanches.
In a significantly windy area, the model could not accurately estimate snow cover profile only with the
snowfall because in a windy area, snow is moved by winds as blowing snow. To obtain more accurate
snow cover profile in windy areas, we have developed an algorithm that can be used to calculate snow
transport by saltation and suspension so that enables the calculation of snow accumulation and
erosion that frequently occur on the surface at wind convergence zones. This algorithm consists of kepsilon model and the snow budget balance proposed by Takeuchi (1975).
To verify this algorithm, we observed wind and snow transport state along the road in Wakkanai,
Hokkaido where an avalanche was occurred on the roadside by a heavy snowstorm. The observation
was conducted from a moving vehicle equipped with meteorological instruments.
Page | 287
955
Modelling the snow-atmosphere energy balance and its implication for wetsnow avalanche formation processes
1
1
1
1
Christoph Mitterer , Benjamin Reuter , Alec van Herwijnen , Charles Fierz , Jürg Schweizer
1
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland
1
The snow-atmosphere energy balance provides the input for various snow cover processes, such as
ablation (melt), sublimation or snow metamorphism. The energy fluxes at the snow surface are key
factors contributing to avalanche formation. Measuring the spatial variability of these fluxes in complex
terrain is virtually impossible. The most reasonable approach is therefore to use a snow cover model
and verify it by measurements at selected locations. We investigate the snow-atmosphere energy
fluxes and its influence on snow avalanche formation processes for the Steintälli basin above Davos,
in the Eastern Swiss Alps. We used the 1-D snow cover model SNOWPACK to compute the energy
balance and its components based on data from three automatic weather stations. One of the stations
is located on a flat field within the basin, while the other two stations are situated on a ridge and on an
inclined southwest-facing slope, respectively. In a first step, we verified the reliability of the simulations
by comparing the energy balance at the southwest-facing slope once computed with data from the
slope and once with extrapolated data from the flat field. In a second step, we investigate the role of
energy input and melt water production within the basin with respect to avalanche formation during two
wide spread wet-snow avalanche cycles in the spring of 2010. Continuous seismic data from a
geophone inserted in the snow cover in an avalanche start zone were used to obtain avalanche
activity data for the basin. We will present results showing the relative importance of either radiation or
turbulent fluxes on the process of wet-snow avalanche formation.
Page | 288
418
Monitoring the temporal evolution of snow cover properties with upwardlooking radar systems
1,2
3,4,5
1
1
6
Lino Schmid , Achim Heilig , Christoph Mitterer , Jürg Schweizer , Robert Okorn , Hansruedi
2
4,5
Maurer , Olaf Eisen
1
2
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland, Institute of
3
Geophysics, ETH Zurich, Zürich, Switzerland, Department of Geosciences CGISS, Boise State
4
University, Boise, United States, Institute of Environmental Physics, University of Heidelberg,
5
Heidelberg, Germany, Alfred Wegener Institute for Polar and Marine Research, Bremehaven,
6
Germany, Electronic & Technology Management (ETM), FH JOANNEUM Gesellschaft mbH,
Kapfenberg, Austria
Snow stratigraphy is a key contributing factor for assessing avalanche danger. So far, only destructive
methods can provide this kind of information. However, destructive methods prevent a continuous
monitoring of the temporal evolution of the snowpack. Furthermore, parameters relevant for avalanche
formation, such as the amount of new snow, the settlement or percolating water, cannot be measured
automatically. Radar technology provides information on the snowpack non-destructively and allows
deriving internal snow properties from its signal response. During three consecutive winter seasons
from 2010-2011 to 2012-2013, we recorded continuous data from upward-looking impulse radar
systems (upGPR) at two different locations. The amount of new snow during a snowfall event was
calculated from the radar signal by subtracting the height of the reflection of the old snow surface from
the height of the new snow surface. Manual measurements of the new snow amount were generally in
good agreement with the values calculated with our radar algorithm. Furthermore, we were able to
track the reflection of the old snow surface for up to 4 months after its initial burial. To verify the
settling signature within the radar signal, we deployed light-weight sensors attached to potentiometers
on the snow surface before every significant snow fall. These sensors settled with the old snow
surface. Settlement curves derived from the radar and measured directly were in very good
agreement. To assess the wetness of the snowpack, we formulated an algorithm based on the
magnitude of reflection amplitudes. High reflection amplitudes correspond to large differences in
permittivity - in our case the transition from dry to wet. Compared to wet-snow avalanche activity and
lysimeter data, the automated pick of the dry-to-wet transition was encouraging, suggesting that such
data may be used to forecast wet-snow avalanches in notoriously difficult to assess avalanche paths.
Page | 289
1073
Does climate change have an impact on avalanche activity? A case study in the
Kapruner Valley/Austria
1
1
1
Antonia Zeidler , Elena Stoll , Paul Dobesberger
1
Institute of Natural Hazards, BFW, Innsbruck, Austria
The Kaprun Valley in Austria reaches from the town Kaprun, located at an altitude of 786 m a.s.l. to
the Wiesbachorn at 3564 m a.s.l. and has a length of about 15 km. A hydropower plant facility is
located in the valley. For safety reasons (staff and infrastructure protection), the VERBUND Hydro
Power AG, have recorded the avalanche activity since the 1950s. Meteorological data are available for
the last 30 years from three weather stations, located at different altitudes (Kaprun: 750 m a.s.l.;
Mooserboden: 2036 m a.s.l. and Sonnblick: 3106 m a.s.l.). Therefore this study focuses on the climate
change and its likely impact on avalanche activity during this 30 year time period.
The analysis of the meteorological data shows a clear upward trend of the annual mean temperatures
as well as the maximum and minimum temperatures at the respective weather stations. The
precipitation trend is not as clear, especially with regard to the annual maxima of the one and three
day precipitation sums: here the annual variance is much greater than the calculated trends.
The avalanche database contains 43 avalanche paths and a total of 5468 avalanche events from
1980-2010. In order to analyse the avalanche activity, especially with regard to climate change, we
defined several avalanche indices: e.g. number of avalanches, avalanche day yes/no, run-out length
and a ratio of wet to dry snow avalanches. In addition, the avalanche paths were grouped into low-,
medium- and high-altitude paths, depending on the altitude of the release area and the run-out zone.
An increasing trend of wet snow avalanches could be observed on the low-altitude paths, whereas at
high-altitude paths no significant trend could be observed.
Page | 290
A6.2b - Ice sheet – ocean – atmosphere interactions
09.07.2013 16:15-17:45, Forum
926
Towards a simple tool for assessing the dynamic behaviour and mass loss of
marine terminating glaciers and ice streams
1
Andreas Vieli
1
Department of Geography, University of Zurich, Zurich, Switzerland
Glaciers and ice sheet outlets that terminate in the ocean are exposed to both atmospheric and
oceanic forcing. Their response, however, is often highly non-linear due to the sensitivity of calving to
glacier geometry (water depth, trough width) as indicated in recent rapid changes of tidewater glaciers
in Alaska and Greenland. This makes interpretation of terminus changes and future predictions difficult
and current large-scale numerical models are still struggling to reproduce such behaviour.
Here a simple approach is proposed to quantitatively assess the dynamic changes of tidewater glacier
termini and to get a first order estimate of potential retreat rates and mass loss. Atmospheric and
oceanic forcing are included through a simple parameterization in the boundary condition at the
calving front. The flux-boundary theory for grounded calving termini of Schoof (2007), with an
extension for variations in glacier width, is used to account for effects of fjord geometry on ice-flux. We
explore the potential use of such a simple approach on current and past examples of changing
tidewater glaciers from the Greenland ice sheet and Alaska. Although this approach is highly reduced,
it provides a physically based tool for assisting interpretation and assessment of past, present and
near future behaviour in tidewater retreat. Crucially, this approach relies on only minimal data (bed
topography and approximate surface mass balance) and is therefore widely applicable.
Page | 291
464
Seismic noise on the Greenland Ice Sheet
1
1
2
2
3
Fabian Walter , Philippe Roux , Claudia Röösli , Stephan Husen , Lüthi P. Martin
1
2
ISTerre, UJF-Grenoble 1, St Martin D'Heres, France, Swiss Seismological Service, ETH Zürich,
3
Zürich, Switzerland, Laboratory of Hydraulics, Hydrology and Glaciology, ETH Zürich, Zürich,
Switzerland
The profound effect of surface melt on ice sheet dynamics is undisputed. Melt water volume and/or
changes thereof can either promote or inhibit basal sliding, depending on the configuration of the
subglacial drainage system. Although the details of this interplay are not fully understood, it is clear
that melt-water enhanced ice sheet flow has to be accurately incorporated in predictive ice sheet
models.
At the same time, open questions concerning the routing of melt water to the glacier bed remain.
Although moulins clearly mark the entry points of surface streams into englacial water channels, water
flow below the glacier surface is difficult to locate and measure. Tracer experiments, pressure sensors
and radio-echo sounding can provide some information, however, only as point measurements or with
limited spatial resolution.
Here we propose the use of seismic monitoring to study seismic waves emitted by melt water flow.
Using data from a campaign seismic network on Greenland's ablation zone, we study the seismic
background noise. This type of seismicity reveals sustained tremor signals analogous to fluid-induced
volcanic tremor. We discuss to what extent the results of seismic array techniques elucidate englacial
water flow and changes thereof.
Page | 292
1016
Sustained seismic tremor detected in Greeland's ablation zone
1
2
1
3
4
Claudia Röösli , Fabian Walter , Stephan Husen , Ginny A. Catania , Lauren C. Andrews , Martin
5
Lüthi
1
2
Swiss Seismological Service SED, ETH, Zurich, Switzerland, ISTerre, UJF-Grenoble 1, St. Martin
3
4
d'Hères, France, Institute for Geophysics, University of Texas, Austin, United States, Institute of
5
Geophysics, University of Texas, Austin, United States, Laboratory for Hydraulics, Hydrology and
Glaciology VAW, ETH Zurich, Zurich, Switzerland
Interaction between melt water and ice is crucial in understanding dynamics of ice sheets and glaciers.
As a large contributor to sea level change, the Greenland Ice Sheet (GrIS) is particularly influenced by
current climate-induced changes in surface melt. Yet at present we have an incomplete understanding
of how melt water within the ice sheet influences the flow and ultimately the loss of ice mass.
Moulins play a key role in englacial water transport as they route large amounts of surface melt water
into the ice and possibly directly to the bed. Rapid changes in this tributary of water flux can perturb
the intraglacial and subglacial drainage system and thus influence subglacial processes, in particular
basal sliding. However, the exact relationship between local ice flow, moulin geometry is not yet fully
understood. The impact is depending on water amount, geometry and evolution of the intra- and
subglacial drainage system on diurnal as well as seasonal time scales.
The recently initiated inter-disciplinary ROUGE (Real-time Observations of Greenland's Under-ice
Environment) project has focused on the interaction between surface melt water drainage and ice
sheet flow. The project's main field campaign took place in summer 2011 on GrIS' ablation zone near
Jakobshavn Isbræ. It consisted of borehole geophysical measurements in combination with monitoring
of surface displacement, surface mass balance and englacial seimic activity.
Here, we focus on the detection of hour-long seismic tremors analogous to fluid-induced signals in
volcanic environments. The source location of the observed seismic signal coincides with the location
of a moulin within the station network. Furthermore, the tremor frequency content correlates with the
water level measured inside the particular moulin. We document the evolution of the seismic signals
during the Greenland summer season, its frequency content and evolution, and present models of
physical processes generating the observed tremor.
Page | 293
553
Ice dolines in East Antarctica - ice-ocean interactions from surface melt water
drainage events
1,2
2
1,2
2
3
Stefan W. Vogel , Alex D. Fraser , Petra Heil , Ben Galton-Fenzi , David Alexander
1
2
Australian Antarctic Division, Kingston, Australia, Antarctic Climate and Ecosystem CRC, Hobart,
3
Australia, School of Geography, Planning and Environmental Management, University of
Queensland, Brisbane, Australia
Surface melting and melt water streams are common features on outlet glaciers along the East
Antarctic coast during summer. One of the big questions about surface melting in Antarctica is the fate
of the melt water? With Antarctic winters being long and cold, most melt water likely refreezes in the
snowpack with little to no impact on the overall mass balance of the ice sheet. One mechanism for
surface melt water to directly drain into the ocean and mass being lost from the ice sheet is drainage
through ice shelves. Ice dolines are linear surface depression, believed to be the remains of drainage
events of melt water lakes. Dolines have been reported from various parts of Antarctica and pose a
plausible mechanism through which significant amounts of freshwater may reach the ocean beneath
ice shelves with potential impact on the ice-shelf and sea-ice environment, Antarctic bottom water
formation and ocean circulation in general.
Here we revisit the topic of surface melt water drainage and report on the evolution of Amery Ice Shelf
Dolines and report on a very recent doline drainage event on the Mawson Coast. Satellite
observations indicate that dolines may be a static feature, which reforms as the original feature moves
with the flow of ice downstream. In addition to the water draining during the lake drainage events both
features (Amery and Mawson coast) are at the receiving end of larger melt water catchment areas and
bear the potential that substantial amounts of surface melt water drains year after year through hidden
openings at the base of the partially snow covered dolines.
Page | 294
239
Subglacial drainage and glaciohydraulic supercooling within the advancing,
marine-terminating Hubbard Glacier, southeast Alaska
1,2
Daniel Lawson
1
2
CRREL, Hanover, United States, Geography, Dartmouth College, Hanover, United States
Supercooled water at the base of glaciers and ice sheets may control subglacial sediment
entrainment, transport, erosion and deposition within the subglacial drainage system wherever
required boundary conditions are met. Observations of Hubbard Glacier document glaciohydraulic
supercooling where subglacial waters emerge along the grounded margin and morainal bank. Passive
upwelling of subglacially discharged water occurs along the ice face from a subglacial system that
presumably includes extensive distributed drainage, but also exhibits turbulent jets emerging from
subglacial conduits and tunnels; this upwelling exhibits characteristics, such as frazil particles and
flocs in transport that are indicative of supercooling conditions. Where deposition on the morainal bank
has created an emergent fan above high tide, frazil terraces and related features graphically
demonstrate that supercooling is occurring. Very limited data on ice surface and bed topography
suggest that conditions beneath the terminal lobe may exist to cause extensive supercooling of
subglacial waters, while the ice marginal observations demonstrate that the upglacier slope of the
morainal bank and low angle, down-glacier slope of the ice surface must meet the supercooling
criteria. Recognition and modeling (Jenkins 2011) suggest plumes of supercooled waters may
importantly reduce the temperature of waters in contact with the glacier, and thereby reduce the loss
of ice to the sea by melting of the submarine ice face and by calving resulting from undercutting of the
exposed ice cliff, while affecting embayment formation and terminus stability.
Page | 295
C2.3e - Clouds, aerosols and precipitation at high latitudes
09.07.2013 16:15-17:45, Studio
734
Aerosol optical characteristics over the Arctic Ocean from ship-borne sky
radiometer measurements
1
Kazuma Aoki
1
University of Toyama, Toyama, Japan
Aerosol optical characteristics are studied using data from ground-based and ship-borne sky
radiometer measurements. We are seeking in this data information on the aerosol optical
characteristics with respect to their temporal and spatial variability and validation of Satellite and
numerical models. We provide the information, in this presentation, on the optical properties of Arctic
aerosol with respect to their temporal and spatial variability. However, these distributions are difficult to
derive because of variability in time and ship-borne measurements. Therefore, Aerosol optical
characteristics were investigated using the measurements from ship-borne sky radiometer (POM-01
MK-II: Prede Co. Ltd., Tokyo, Japan) over the ocean. We started the monitoring of aerosols optical
characteristics since 1994, by using a sky radiometer (http://skyrad.sci.u-toyama.ac.jp/). The sky
radiometer is an automatic instrument that takes observations only in daytime under the clear sky.
Observation of aureole interval was made every five minutes by once on-board research vessel. Shipborne type, GPS provides the position with longitude and latitude and heading direction of the vessel,
and azimuth and elevation angle of sun. Horizon sensor provides rolling and pitching angles. The
aerosol optical characteristics were computed using the SKYRAD.pack version 4.2 developed by
Nakajima et al. (1996). In this study, we present the temporal and spatial variation and the relationship
of Aerosol optical thickness and Ångström exponent over the Arctic Ocean on-board R/V Mirai
(JAMSTEC) during 40N to 70N and ground-based measurements at Sapporo/Hokkaido (43N, 141E),
North part of Japan. The obtained aerosol optical thickness clearly showed spatial variability over the
Arctic Ocean. Especially, it was low aerosol optical thickness at over the Arctic Ocean, compared to
the East Asia.
Page | 296
773
In-situ measurements of aerosol-cloud interactions in warm and freezing
conditions at Puijo, a semi-urban measurement station
1
1,2
1
2
3
Ari Leskinen , Harri Portin , Jarkko Hirvonen , Sami Romakkaniemi , Heikki Lihavainen , Ari
2,3
1,2
1
Laaksonen , Kari E.J. Lehtinen , Mika Komppula
1
2
Kuopio Unit, Finnish Meteorological Institute, Kuopio, Finland, Department of Applied Physics,
3
University of Eastern Finland, Kuopio, Finland, Climate Change, Finnish Meteorological Institute,
Helsinki, Finland
The Puijo measurement station (62°54'34'' N, 27°39'19'' E, 306 m above sea level, 224 m above the
surrounding lake level) has provided continuous data on aerosol-cloud interactions since 2006. The
station is located on the top of an observation tower, which resides on a 150 m high hill. The top of the
tower is covered by cloud 15 % of the time, mainly in the autumn, dominated by warm clouds, and in
the winter, dominated by freezing conditions with temperatures down to -30 °C.
During the warm cloud periods we measure continuously the cloud droplet size distribution (3-50 µm)
with a Cloud Droplet Probe. The device is mounted on a revolving swivel, which keeps the inlet facing
the wind. During special campaigns, we also use a Cloud, Aerosol and Precipitation Spectrometer in
order to separate droplets and ice crystals in the cloud.
By using a special twin-inlet we are able to separate the total aerosol from the cloud interstitial
(unactivated) particles and thus estimate the properties of the activated particles. This analysis is
based on continuous measurement of aerosol size distribution and light absorption and scattering, and
campaignwise measurement of aerosol chemical composition by using an Aerosol Mass Spectrometer
and a Single Particle Soot Photometer.
We also measure continuously the concentrations of some trace and greenhouse gases (NO, NO x,
SO2, O3, CO2, and CH4), and meteorological parameters (temperature, humidity, pressure, wind,
visibility, and precipitation). During winters we use several indicators for identifying icing conditions.
Until 2013, we have detected and analyzed some 600 cloud events, about half of which with freezing
conditions. So far, we have inspected the effect of local pollutant sources on the aerosol composition
and its cloud activation behaviour, as well as the effect of cloud processing on the aerosol properties.
Page | 297
946
Impact of aerosols on the radiative forcing of mixed-phase deep cloud system
inferred from satellite and ground observations
1
Zhanping Li
1
University of Maryland, College Park, United States
For mixed-phase deep convective clouds, aerosol's invigoration effect is a dominant mechanism
governing the interactions between aerosols and clouds due partially to the release of latent heat as
cloud droplets convert into ice crystals. Such an effect can impede upon cloud radiative forcing
significantly by altering cloud microphysics, cloud height and cloud extent, but little is known on the
magnitude or even the sign for each of the components. Using a large ensemble of data from satellite
and surface measurements, we are trying to sort out and estimate the effects. Using the rich A-Train
satellite data, an algorithm to automatically identify all deep clouds was developed and the relationship
between these clouds and aerosol loading is examined. Preliminary results show that there is a
significant enhancement in both shortwave CRF and longwave CRF with increasing aerosol index (AI)
over oceans and aerosol optical depth (AOD) over land for mixed-phase clouds; no significant change
was seen for liquid clouds. Cloud-top height, cloud thickness and cloud ice processing appear to be
positively correlated with AI/AOD, which indicates that the correlation between CRF and aerosol
loading may be explained via microphysical and invigoration effects. Considering the inherent
limitation, we also employ the ARM ground-based data to independently estimate these aerosolmediated cloud radiative forcing.
Page | 298
B3.1c - General dynamics
09.07.2013 16:15-17:45, Wisshorn
840
Isentropic analysis of polar cold air mass streams in the northern hemispheric
winter
1
2
3
4
Toshiki Iwasaki , Takamichi Shoji , Masahiro Sawada , Kotaro Takaya
1
Department of Geophysics, Graduate School of Science, Tohoku University, Sendai, Japan,
2
3
Graduate School of Science, Tohoku University, Sendai, Japan, Tokyo University, Kashiwa, Japan,
4
JAMSTEC, Yokohama, Japan
An analysis method is proposed of polar cold air mass streams from the generation to the
disappearance. It designates a threshold potential temperature at around the turning point of the
extratropical direct (ETD) meridional circulation from the downward to the equatorward in the massweighted isentropic zonal mean (MIM), and clarifies the geographical distributions of the cold air mass,
the negative heat content (NHC), their horizontal fluxes and their genesis/loss rates, on the basis of
conservation relations of the air mass and thermodynamic energy.
January mean cold air mass flux below =280K in the northern hemispheric winter was estimated using
the reanalysis. The polar cold air mass has two mainstreams, hereafter called as East Asian (EA)
stream and the North American (NA) stream. The former grows over the northern part of the Eurasian
continent, flows eastward, turns down southeastward toward East Asia via the Siberia and disappears
over the western North Pacific Ocean. The latter grows over the Arctic Ocean, flows toward the East
Coast of North America via Hudson Bay and disappears over the western North Atlantic Ocean. The
streams coincide well in their routes with the cold surges, which has been discussed by many authors.
The isentropic analyses allow us to qualitatively analyze ensemble effects of intermittent cold surges.
In their exit regions of the cold air mass streams, wave-mean flow interactions transfer the angular
momentum from the streams to the upward Eliassen-Palm flux and convert the available potential
energy into wave energy.
Page | 299
547
Interannual variability of the East Asian winter monsoon and associated
modulations of upper-level planetary waves
1
1,2
Koutarou Takaya , Hisashi Nakamura
1
Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology,
2
Yokohama, Japan, Research Center for Advanced Science and Technology, University of Tokyo,
Tokyo, Japan
Interannual variability of the East Asian winter monsoon has been examined on the basis of
observational data over the 50 recent years. Although the monsoon activity itself is confined into the
lower troposphere, its midwinter variability tends to be associated with upper-tropospheric geopotential
height anomalies similar to the Eurasian (EU) and Western Pacific (WP) teleconnection patterns. In
the “WP-like” pattern, a meridional dipole of upper-level height anomalies is evident over the Far East
region. In the “EU-like” pattern, a wavy signature can be found over the Eurasian continent and even
the North Atlantic, implying that source of the wavy signal may be found over the North American
continent.
The WP- and EU-like patterns are found to accompany pronounced modulations of the climatological
evolution of the upper-tropospheric planetary waves from late autumn to midwinter. Enhanced
monsoon activity in January involves extreme seasonal evolution of a planetary-wave ridge with
positive height tendencies from November to January over eastern Siberia and Alaska, while the
corresponding tendencies are anomalously negative with weakened monsoon activity. Furthermore,
the stronger monsoon also accompanies an enhanced seasonal decline of height over the midlatitude
North Pacific, corresponding to the enhanced southward development of a planetary-wave trough.
Those signals can be found stronger in WP-like pattern than in the EU-like pattern. The variability of
midwinter monsoon activity associated with WP/EU-patterns is also accompanied by the noticeable
variability of seasonal development of the planetary waves over the Euro-Atlantic sector, which is
more evident in the EU-like pattern than in the WP-like pattern.
Page | 300
804
Origin and behavior of wavenumber 2 during vortex-splitting stratospheric
sudden warming events in the Northern and Southern Hemispheres
1
1
2
3
Toshihiko Hirooka , Tsuyoshi Ohata , Hiroaki Naoe , Hitoshi Mukougawa
1
2
Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan, Ozone Layer
3
Monitoring Office, Japan Meteorological Agency, Tokyo, Japan, Disaster Prevention Research
Institute, Kyoto University, Uji, Japan
Stratospheric sudden warmings are caused by enhanced planetary waves and classified into vortex
splitting and vortex displacement events. In vortex splitting events, planetary waves of zonal
wavenumber 2 (wave 2) are predominant in the stratosphere and break the stratospheric polar vortex
into two pieces. However, the origin and behavior of wave 2 are still unclear. In the present study, the
origin and behavior of wave 2 are examined for typical cases of vortex splitting events in the Northern
and Southern Hemispheres by the use of the ERA-Interim reanalysis data. Here, we investigate
events occurring in the Northern Hemisphere (NH) in January 2009, February 1989 and December
1984, along with an event in the Southern Hemisphere (SH) in September 2002. It is found that wave
2 components were intensified in all the events but their traveling features are fairly different between
the NH and SH cases: Wave 2 components in the NH were quasi-stationary while those in the SH
showed eastward traveling features. It is also revealed that blocking phenomena in the troposphere
played an important role for the development of wave 2 for all the events: In the events of the NH, the
upward propagation of wave packets originated from a blocking ridge over Alaska and their following
eastward propagation brought about wave 2 amplification. On the other hand, the event in the SH was
brought about by upward propagation of wave packets emanating from a blocking ridge over the
South Atlantic. However, such upward propagation of wave packets seems to strengthen only wave 1
components which were still stronger than wave 2 during the event.
Page | 301
901
Vortex-vortex interactions for the maintenance of blocking: the selective
absorption mechanism
1
2
Akira Yamazaki , Hisanori Itoh
1
2
Earth Simulator Center, JAMSTEC, Yokohama, Japan, Earth and Planetary Sciences, Kyushu
University, Fukuoka, Japan
A new block maintenance mechanism, the selective absorption mechanism (SAM), is proposed.
According to this mechanism, which is based on vortex-vortex interactions (i.e., the interactions
between a blocking anticyclone and synoptic eddies with the same polarity), a blocking anticyclone
actively and selectively absorbs synoptic anticyclones (strictly, air parcels with low potential vorticity).
The blocking anticyclone, which is thus supplied with low potential vorticity of the synoptic
anticyclones, can subsist for a prolonged period, withstanding dissipation. The SAM was verified
through real case studies and numerical experiments.
In the case studies, trajectory analyses were conducted. Ten actual cases of blocking were examined.
Trajectories were calculated by tracing parcels originating from synoptic anticyclones and cyclones
located upstream of the blocking. Parcels starting from anticyclones were attracted to and absorbed by
the blocking anticyclone, whereas parcels from cyclones were repelled by the blocking anticyclone.
The numerical experiments performed here were based on the nonlinear equivalent-barotropic
potential vorticity equation, with varying conditions with respect to the shape and amplitude of
blocking, the characteristics of storm tracks (displacement and strength), and the characteristics of
background zonal flow. The experiments indicate that the SAM effectively maintains blocking,
independently of the above conditions. By applying a channel model on a beta plane, numerical
experiments were conducted using a uniform background westerly with a jet. Results show that the
presence of a jet promotes the effectiveness of the SAM. Two spherical model experiments were also
performed; the SAM was as effective as the beta-plane model in explaining the maintenance of
blocking. Moreover, a quantitative experiment showed that the SAM maintained a real block under
realistic meteorological conditions, demonstrating that the SAM is effective.
The above results verify that the SAM is an effective general maintenance mechanism for blocking.
Page | 302
357
Predictability and Dynamics of Persistent Blocking over Russia in Summer
2010 Examined by Ensemble Forecast Datasets
1
2
3
Hitoshi Mukougawa , Aki Fujii , Yuhji Kuroda
1
2
Disaster Prevention Research Institute, Kyoto University, Uji, Japan, Graduate School of Science,
3
Kyoto University, Kyoto, Japan, Meteorological Research Institute, Tsukuba, Japan
This study investigates the predictability and maintenance mechanism of the anomalously long-lasting
strong blocking high over Western Russia from late-July to mid-August 2010 using JRA-25/JCDAS
reanalysis dataset, a hindcast experiment performed on MRI (Meteorological Research Institute)/JMA
(Japan Meteorological Agency) AGCM, and the operational JMA 1-month ensemble forecast.
It is found that the predictability of the blocking is considerably reduced during the maintenance period
of the blocking at the end of July in comparison with the adjacent periods. A Lag-regression analysis
using the operational JMA 1-month ensemble prediction shows that the deepening of a cyclonic
anomaly immediately upstream of the blocking until 4 days prior to the forecast time is significantly
related to the blocking enhancement, whereas upstream perturbations before that time are irrelevant
to the blocking development. The anticyclonic vorticity forcing due to the upper tropospheric horizontal
divergence associated with the upstream cyclone enhances the blocking. Thus, the immediate forcing
process for the blocking maintenance would be connected with the limited predictability during this
period.
It is also revealed by examining the reanalysis dataset that the interaction between the climatologically
enhanced horizontal convergence and the coexisting anticyclonic anomaly over the western part of the
Eurasian continent in the upper troposphere primarily enforces the blocking over Russia through the
vortex stretching in early August 2010. Moreover, a regression analysis using the JMA ensemble
prediction indicates that the predicted amplification rate of the blocking over Russia becomes larger
with the increase of the anticyclonic anomaly in the climatologically convergent region. This result also
confirms the importance of the maintenance mechanism of the blocking through the vortex stretching.
In comparison with other blocking events, we find that these maintenance mechanisms are inherent to
the blocking over Russia in summer 2010, which would be related to its exceptional persistence.
Page | 303
1134
Using enstrophy transport as a diagnostic to identify flow regime
transformation
1
1
2
Andrew D. Jensen , Anthony Lupo , Igor I. Mokhov
1
Soil, Environmental, and Atmospheric Sciences, University of Missouri, Columbia, United States,
2
A.M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Moscow, Russian
Federation
Previously obtained results demonstrated that, in an atmosphere that is barotropic or approximately
so, the sum of the positive Lyapunov exponents in the attractor would be approximately equal to the
area integrated enstrophy. As such, area integrated enstrophy (IRE) can be viewed as a measure of
the stability or the predictability within a flow regime. Low values represent a more stable, predictable
regime. Subsequent studies demonstrated the utility of IRE in identifying the onset and decay of
blocking events. In identifying block onset and decay it was found that IRE increases dramatically over
a small window of time, and then decreases again when the flow stabilizes. The IRE may also have
utility as a variable that can identify flow regime transformation in a general sense. However, the
weakness in this technique is that it is unclear whether there is a certain rate of increase or a threshold
value that must be crossed in order to successfully identify regime transformation. To that end, the
barotropic Vorticity Equation can be multiplied by vorticity to get an enstrophy equation, and then
integrated over area. Applying the previously obtained results mentioned above, the sum of the
Lyapunov exponents can be set approximately equal to the integral of advection or flux of enstrophy in
a Cartesian atmosphere with pressure as the vertical coordinate. As a result, the transport or flux of
enstrophy can also be used for a diagnostic of flow instability. This was tested using several case
studies of blocking and shown to be a useful diagnostic for regime transformation.
Page | 304
A3.3 - Decadal climate prediction
09.07.2013 16:15-17:45, Schwarzhorn
976
Reliability of decadal predictions
1,2
2,3
2,3
4,5
Susanna Corti , Antje Weisheimer , Tim N. Palmer , Francisco Doblas-Reyes , Linus
2
Magnusson
1
2
3
Climate Dynamics, ISAC-CNR, Bologna, Italy, ECMWF, Reading, United Kingdom, Department of
Physics, Atmospheric, Oceanic and Planetary Physics, National Centre for Atmospheric Science,
4
Oxford, United Kingdom, Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain,
5
Institut Català de Ciències del Clim, Barcelona, Spain
The reliability of multi-year predictions of climate is assessed using probabilistic Attributes Diagrams
for near-surface air temperature and sea surface temperature, based on 54 member ensembles of
initialised decadal hindcasts using the ECMWF coupled model. It is shown that the reliability from the
ensemble system is good over global land areas, Europe and Africa and for the North Atlantic, Indian
Ocean and, to a lesser extent, North Pacific basins for lead times up to 6-9 years. North Atlantic SSTs
are reliably predicted even when the climate trend is removed, consistent with the known predictability
for this region. By contrast, reliability in the Indian Ocean, where external forcing accounts for most of
the variability, deteriorates severely after detrending.
The results from ECMWF decadal hindcasts are compared with a multi-model ensemble from the
CMIP5 dataset.
Page | 305
826
Decadal predictability of tropical cyclones frequency in CMIP5 models
1
2
1
1
1
Alessio Bellucci , Enrico Scoccimarro , Panos Athanasiadis , Andrea Borrelli , Silvio Gualdi
1
2
CMCC, Bologna, Italy, INGV, Bologna, Italy
The sources of predictability of Tropical Cyclones (TC) activity have been explored at both seasonal
and long-term century time scales, using state-of-the-art coupled general circulation models (CGCM).
Promising results recently achieved with near-term prediction systems, performed with a realistic
initialization of a dynamical model, makes now feasible the inspection of TC predictability over the
decadal range.
Here we investigate the predictability of Tropical Cyclones (TC) frequency in a set of CMIP5 CGCMs.
The analysis is restricted to models featuring a finer than 1.5 degrees atmospheric resolution, so as to
allow a sufficiently accurate representation of TC dynamics.
The detection of TCs is based on 6-hourly data from a multi-model ensemble of near-term (decadal)
predictions for the 1960-2035 period, performed following the CMIP5 protocol. Specifically, the
relationship between low frequency regional-scale fluctuations in the sea-surface temperatures and
coordinated changes in the TCs frequency is analysed.
Page | 306
1072
Seasonal-to-interannual variability of precipitation over southeastern South
America in CMIP5 decadal hindcasts
1
1
Paula Gonzalez , Lisa Goddard
1
International Research Institute for Climate and Society, Columbia University, Palisades, United
States
A set of decadal hindcasts has been designed for CMIP5 to explore the effect of initializing the
coupled models with information about the current state of the climate system. Some skill for the next
year-to-decade may be gained if one can predict aspects of natural climate variability in addition to the
anthropogenic trend. We explore the performance of the hindcasts over South Eastern South America
(SESA), focusing mainly on precipitation. Over the 20th Century, this region experienced large trends,
showed decadal-scale variability, and also exhibited strong seasonal-to-interannual variability, mainly
due to an ENSO teleconnection.
Using a subset of CMIP5 initialized decadal hindcasts we show that some models are better able than
others to predict ENSO-related teleconnections over this region, even at several years lead time.
There is a suggestion that the fidelity of the annual cycle, and particularly its timing, may be one factor
in the better performance of these models. However, a better performance at seasonal-to-interannual
timescales does not necessarily lead to more accurate decadal predictions or a better representation
of the multi-decadal trends. The properties of the resulting 15-member multi-model ensemble will also
be presented.
Page | 307
928
Decadal prediction skill with the IPSL-CM5A model: impact of horizontal
atmospheric resolution and of climate sensitivity bias
1
1,2,3
4
1
Sulagna Ray , Juliette Mignot , Didier Swingedouw , Eric Guilyardi
1
2
LOCEAN/IPSL, Paris, France, Climate and Environmental Physics, Physics Institute, Univ Bern,
3
Bern, Switzerland, Oeschger Centre for Climate Change Research, University of Bern, Bern,
4
Switzerland, LSCE/IPSL, Paris, France
Various climate models in the CMIP5 framework are used to assess the decadal predictability of global
and regional climate. Here, in order to concentrate on understanding physical mechanisms at play, we
quantify the predictability skill in a single climate model: IPSL-CM5A. Two versions of the model,
differing by the horizontal atmospheric resolution, are initialized by nudging to observed SST
anomalies for the 1949-2005 period. We assess the effect of initialization in both systems by
comparing the initialized simulations to various ocean reanalyses. Special focus is put on the
subsurface ocean, where no initialization is done directly in order to maintain dynamical consistency in
the model. As a second step, the performances of hindcasts launched from these initialized
simulations are assessed as compared to the initialised simulation (potential predictability) as well as
to the observations (effective predictability). SST in the tropical Atlantic and in the western tropical
Pacific is found to be potentially and effectively predictable at lead time 1 year. The hindcasts also
display significant potential predictability for averaged lead time of 6-9 years in the tropical Atlantic,
North Atlantic and North Pacific regions. Results will be presented with a focus on the influence of the
atmospheric resolution on the predictability skill as well as the associated physical mechanisms and
considerations on the effect of the overestimated climate sensitivity of the IPSL-CM5A model.
Page | 308
980
Seasonal-decadal prediction with the EnKF and NorESM: a twin experiment
1
2
3
2
1
Francois Counillon , Ingo Bethke , Noel Keenlyside , Mats Bentsen , Laurent Bertino , Fei Zheng
1
2
3
NERSC/BCCR, Bergen, Norway, Uni/BCCR, Bergen, Norway, UiB/BCCR, Bergen, Norway,
4
ICCES/IAP, Beijing, China
4
Seasonal to decadal predictions are investigated using an advanced flow dependent data assimilation
method together with the Norwegian Earth System model (NorESM). NorESM is a fully coupled
system based on the Community Climate System Model version 4, which includes an ocean, an
atmospheric, a sea-ice and a land model. A twin experiment methodology is employed in order to
demonstrate the capability of the initialisation method in absence of model biases. A coarse version of
the model is used (3.6∘ ocean grid) and the system is tested for assimilating synthetic sea surface
temperature (SST) over 10 cycles. Each cycle consists of a 10-year assimilation phase followed by a
10-year prediction phase. The deterministic Ensemble Kalman Filter assimilates monthly SST and its
accuracy is compared to an ensemble free run (Free) and a perfect initialisation ensemble run
(Perfect). The results indicate that EnKF-SST improves sea level, ice concentration and 3D
hydrography compared to Free. Improvements are largest near the surface, but are retained for a
longer period at depth. Near-surface improvements are largest in the tropics, while improvements at
intermediate depths are found in regions of large-circulation currents, zone of convection, and at the
Mediterranean Sea outflow. However, the benefits are small compare to the perfect initialisation - in
particular at depth - suggesting that more observations are necessary. The EnKF-SST system is also
tested for standard indices - AMOC, SPG, STG, AMO and NINO3. EnKF-SST has skills for all indices
in analysis mode. The predictive skill of EnKF-SST for these indices are compared to Perfect and
persistence. EnKF-SST outperforms persistence for AMOC and also for SPG if the initial bias is
corrected. It also outperform persistence for NINO3 for the first five months. EnKF-SST, persistence
and Perfect shows no skill for AMO and STG beyond 1 year prediction.
Page | 309
673
CMIP5 multi-model initialized decadal hindcasts for the mid-1970s shift and
early 2000s hiatus and predictions for 2016-2035
1
1
Gerald Meehl , Haiyan Teng
1
National Center for Atmospheric Research, Boulder, Colorado, United States
Hindcasts initialized with observations show skill over and above uninitialized simulations in a 16
member multi-model ensemble from the CMIP5 ten-year decadal climate prediction experiments for
the mid-1970s climate shift, when the tropical Pacific warmed over a decade and globally averaged
temperature rapidly increased, and the early 2000s hiatus when the tropical Pacific cooled over a
decade and global temperatures warmed little. A 30 year initialized hindcast for the available 14
member multi-model ensemble shows added skill over the Pacific compared to the uninitialized
historical simulations, and somewhat lower amplitude global warming that is closer to observations
compared to the uninitialized simulations. A 30 year prediction from those 14 model simulations
initialized in 2006 shows global warming for the 2016-2035 period compared to the 1986-2005
reference period of +0. 62C +/- 0.33C (2 standard deviations) compared to +0.74C +/-0.24C for the
free-running uninitialized model projections for that same time period. This slower warming is partly
because the initialized predictions start at 2006 during the hiatus period that is cooler than the
uninitialized state, and partly because the bias adjustment procedure reduces a larger-than-observed
warming trend in hindcasts. Consequently, uninitialized bias-adjusted hindcasts also produce
improved simulations compared to the standard uninitialized simulations and observations.
Page | 310
B1.2 - Improved use of Earth observations
09.07.2013 16:15-17:45, Seehorn
531
Assimilation of hIgh-density pressure observations using an ensemble Kalman
filter system
1
1
Clifford Mass , Luke Madaus
1
Atmospheric Sciences, University of Washington, Seattle, United States
Large numbers of surface pressure observations are now becoming available from a variety of
mesoscale networks, and most recently from sensors in smartphones. Pressure is a uniquely valuable
surface observation that expresses the structure of the atmosphere above, and does not possess
many of the bias and representational error problems of other variables, such as temperature and
wind.
This presentation will describe the use of very dense surface pressure networks in a high-resolution
(4-km) ensemble Kalman filter system run over the Northwest U.S. over an extended period. As
described in this talk, innovative quality control and bias correction preprocessing are required to
derive maximum value from mesonet pressure observations. The results of extended experiments will
be presented in this talk.
Page | 311
512
Uncertainties in determining the targeting observation aea of a heavy rainfall
event
1
1
Zhiyong Meng , Ling Huang
1
Department of Atmospheric and Oceanic Sciences, Peking University of China, Beijing, China
Targeting observation has been a hot topic due to the limitation of observing resources. It aims to
locate an area around a certain weather system in which adding more observations may produce
much more benefit to the forecast accuracy than in anywhere else. This data utilization problem has
been mainly examined from deterministic point of view with more and more mixing results on its
effectiveness. This work is to examine the uncertainties in determining the targeting area in a
southwest vortex case in China in June 2008 in a framework of ensemble forecast.
The targeting area of this event was examined through two different ways. One is through direct data
assimilation experiments by exploring the impact of assimilating synthetic observation at the initial time
on the 24-h rainfall and vortex simulation through Observing System Simulation experiment (OSSE)
via WRF-3DVar. In the frame work of ensemble forecast, two members with an initial difference similar
to the observation error had different targeting areas. Some members were even not sensitive to the
data assimilation thus no targeting area. This result indicates large uncertainties in the targeting area
determination. The uncertainty was further confirmed when we tried a different way to define the
targeting area through calculating the correlation between the 24-h total precipitation and the initial
variables. We found that the area with the maximum correlation in the initial field didn't match the
targeting area determined by the DA/OSSE method.
These results demonstrate that the location of targeting area is very sensitive to the initial error, model
error, and the adopted methodology. The large uncertainties may hint a limited potential in the
operational practice of targeting observation.
Page | 312
670
Impacts of observation data with different frequency on nowcasting accuracy
1
1
2
1
1
1
Laura Huang , George Isaac , Grant Sheng , Monika Bailey , Ivan Heckman , Faisal Boudala , Robert
1
Crawford
1
2
Environment Canada, Toronto, Canada, York University, Toronto, Canada
This study presents an analysis of the impact of different frequency observation data on nowcasting
accuracy. Accurate nowcasting requires purposeful-built models with higher spatial resolution,
improved location specificity, increased temporal resolution of observation data and greater frequency
of model updating than existing models. Since there is a general lack of numerical models specifically
designed for nowcasting, different numerical models and / or ensembles which were originally
designed for short or midterm forecasts are now also being used for nowcasting. At Environment
Canada, a weighting, evaluation, bias correction and integrated system (WEBIS) has been developed
for generating optimal nowcasts by integrating observation data and different numerical forecast
prediction (NWP) models. This study assesses the effect of using different frequency observation data
on nowcasts' accuracy. Surface observations at two frequencies (1 min vs. 1 hour interval) were
tested for generating integrated nowcasts. Three different NWP models were used as background
models for generating integrated nowcasts. The impact on nowcasting accuracy using two different
frequency observations are analyzed for nowcasts of temperature, relative humidity, wind speed, wind
direction and wind gust. By analyzing the verification results from these five forecasting variables, it is
found that nowasting accuracy is greatly improved with high frequency updating of observation data.
Page | 313
352
Applications of ATMS/AMSU humidity sounders for hurricane study
1
1
2
3
Xiaolei Zou , Qi Shi , Zhengkun Qin , Fuzhong Weng
1
Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, United
2
States, Center of Data Assimilation for Research and Application, Nanjing University of Information
3
Science and Technology, Nanjing, China, Center for Satellite Applications and Research,
NOAA/NEDIS, Camp Springs, United States
Tropical cyclone (TC) structures consisting of eye, eyewall and rainband are clearly resolved by the
ATMS/AMSU microwave humidity sounders at a 15-km resolution. It is firstly shown that TC center
location and the radius of maximum wind could be well determined from MHS window channel 2 at
157 GHz. A revised quality control (QC) algorithm for ATMS/MHS humidity sounders aiming at
identifying data points for which clouds have negligible impacts on ATMS/MHS humidity sounder
observations is then developed and implemented in the Hurricane Weather Research Forecast
(HWRF) system. The QC algorithm is based on the ice water path (IWP) and liquid water path (LWP),
which can be derived from two window channels of ATMS/AMSU humidity and temperature sounders
respectively. Finally, impacts of ATMS/MHS data assimilation on hurricane track and intensity
forecasts are demonstrated for Hurricane Sandy with different forecast leading times (e.g., 1-8 days)
before Sandy made landfall on October 30, 2012. It. Over ocean, the MHS window channel derived ice
water path (IWP) is used to firstly remove those data with cloud scattering effects. Improvements and
degradations by the assimilation of microwave humidity sounder data on hurricane forecasts with and
without implementing the revised QC algorithm are analyzed. Areas for further improvements in
satellite data assimilation using HWRF are discussed.
Page | 314
430
Greenhouse gases analysis as part of the Monitoring of Atmospheric
Composition and Climate (MACC-II) project
1
1
1
2
3
Sebastien Massart , Anna Agusti-Panareda , Richard Engelen , Cyril Crevoisier , Sandrine Guerlet ,
3
3
Otto Hasekamp , Ilse Aben
1
2
European Centre for Medium-Range Weather Forecasts, Reading, United Kingdom, Laboratoire de
3
Météorologie Dynamique/IPSL/CNRS, Ecole Polytechnique, Palaiseau, France, Space Research
Organization Netherlands, Utrecht, Netherlands
As part of the pre-operational Monitoring of Atmospheric Composition and Climate -Interim
Implementation- (MACC-II) project, global atmospheric greenhouse gas concentrations are forecasted
and analysed using the infrastructure of the ECMWF Integrated Forecasting System (IFS).We will
present the analysis of methane (CH4) constrained by the assimilation of satellite measurements.
The assimilated data are retrievals from the TANSO and IASI instruments respectively onboard
GOSAT and MetOp-A. TANSO retrievals are more sensitive to the lower troposphere while IASI
retrievals are more sensitive to the mid-troposphere. TANSO measurements are retrieved mainly over
land while IASI measurements are currently retrieved only in a tropical band between 30ºS and 30ºN.
We will present how the difference in the instrument retrievals impacts the analysis of tropospheric
CH4. To assess this impact, we use independent data from the Integrated Carbon Observation System
(ICOS) network and from the Total Carbon Column Observing Network (TCCON).
The current assimilation system produces CH4 analyses using the IFS 4D-Var assimilation system.
The used background error covariance matrix (BECM) is fixed and was computed using the NMC
method. We also diagnose a flow-dependent BECM combining an ensemble method with the
variational analysis. In addition to the perturbation imposed on the meteorological parameters by the
IFS Ensemble Data Assimilation system, we also impose perturbations on the CH4 fluxes and
retrievals. The flux perturbations increase the diagnosed background error standard deviation for the
lower troposphere compared to the one obtained from the NMC method. We will characterise how this
modifies the respective weight of the instruments, as increasing the background error standard
deviation for the lower troposphere means giving more confidence to the observations where TANSO
is the more sensitive. We will moreover investigate the impact of each instrument on the diagnosed
ensemble-based BECM by removing alternatively one of them instead of perturbing their
measurements.
Page | 315
B7.2b - Atmosphere Land Cryosphere Interactions
09.07.2013 16:15-17:45, Sertig
1121
High spatial resolution measurements and models for air quality studies in the
Baltimore/Washington area: DISCOVER-AQ
1
1
1
1
1
1
1,2
Russell Dickerson , D. Allen , H. Arkinson , L Brent , Tim Canty , D. Goldberg , Hao He , C.
3
1
3
1
1
1
3
Loughner , C. Liaskos , K Pickering , A. Ring , R. Salawitch , J. Stehr , A. M. Thompson
1
2
Atmos and Ocean Science, Dept AOSC. Univ. Maryland, College Park, United States, ESSIC,
3
College Park, United States, NASA Goddard Space Flight Center, Greenbelt, United States
An intensive field and modeling campaign was conducted over the Baltimore Washington area in July
2011. Observations included in situ measurements from aircraft (NASA and MDE), sondes, and a
ship, as well as remote sensing from the surface and NASA and NOAA satellites. Numerical
simulations included CMAQ in the forecast mode and high resolution WRF/CMAQ runs in the analysis
mode. The objectives were to determine the degree to which remotely sensed data relate to surface
concentrations and to advance our understanding of the fundamental meteorology and chemistry of
ozone and haze episodes in the Mid Atlantic States. Results indicate the importance of alkyl nitrates in
sequestering NOx to extend its lifetime leading to model improvements in capturing the spatial scale of
smog events. AURA/OMI measurements were highly valuable in this discovery, and the findings have
implications for interstate transport relevant to pollution control policy. In mesoscale meteorology, the
Chesapeake Bay played a central role in air circulation. The Bay breeze and elevated reservoir of
pollutants were seen to be involved in exacerbating some, but preventing other air quality violations in
Maryland. WRF with standard 12-km resolution did not reproduce these features, while WRF with
enhanced 1.3-km resolution (1.3) was able to simulate the vertical distribution of trace gases and their
impact on air quality in downwind states.
Page | 316
991
The effects of absorbing aerosols on snow/ice albedo over the Arctic
1
1
1,2
1,3
N. Christina Hsu , Si-Chee Tsay , Andrew Sayer , Corey Bettenhausen
1
2
NASA/Goddard Space Flight Center, Greenbelt, United States, GESTAR/USRA, Columbia, United
3
States, SSAI, Lanham, United States
Among the many components that contribute to air pollution, absorbing aerosols such as dust and
smoke play an important role due to its biogeochemical impact on the ecosystem and its radiativeforcing effect on the climate system. In East Asia, dust storms frequently accompany the cold and dry
air masses that occur as part of springtime cold front systems. On the other hand, biomass burning
and wildfires also often occur over eastern and northern Russia during this season and generate
extensive smoke plumes. Consequently, these anthropogenic and natural air pollutants, once
generated over the source regions, can be transported out of the boundary layer into the free
troposphere and can travel thousands of kilometers across the Pacific into the United States or directly
into the Arctic. In this paper, we will use satellite data from MODIS and VIIRS to investigate the effects
of these absorbing aerosols on the albedo of snow/ice surfaces at high latitudes over the last decade.
The direct radiative forcing due to these aerosols exerted in the Earth's energy budget will also be
quantified and discussed.
Page | 317
111
Effect of the deposition processes of black carbon on the spectral and
broadband albedo of snow in North East China
1
1
2
2
3
Gallet Jean-Charles , Christina Pedersen , Wang Zhangwei , Xiaoshan Zhang , Johan Ström
1
2
Norwegian Polar Institute, Tromsø, Norway, Research Center for Eco-Environmental Sciences,
3
Chinese Academy of Sciences, Beijing, China, Stockholm University, Department of Applied
Environmental Science, Stockholm, Sweden
Black Carbon (BC) atmospheric particles originate from incomplete combustion of fossil fuel and
biomass. When deposited on the surface, even small amounts of BC can reduce the snow albedo.
However, the lack of observations and poor process understanding makes estimates of its climate
impact uncertain.
We have conducted measurements of semi-continuous BC concentrations in snow surface and snow
spectral albedo at CAS Research Station of Changbai Mountain Forest Ecosystem in North East
China during three snow seasons 2009/10, 2010/11 and 2011/12. Because of the dry and cold winter
that prevalent most of the time in that area, it is possible to determine with a quite good confidence
level the deposition processes of BC onto the snow surface, meaning dry or wet deposition.
While a dry process deposits BC only at the top surface of the snow, a wet process will bury the BC
deeper into the snowpack. Because of the wavelength absorption dependence of pure ice and the
deposition processes that will locate the BC on top or into the snowpack, a difference in the spectral
signature of the albedo of snow is expected. It will therefore affect in a different manner the broadband
albedo which is the variable of interest for input in global model. We wish therefore to emphasis the
importance of the deposition processes of BC onto snow surfaces, not only to improve
parameterizations in global model but also because it could modify the snow cover extent in Changbai
Mountain and therefore strongly impact the climate.
Page | 318
442
Climatic drivers for interannual variation in streamflow in Taylor Valley,
Antarctica: evaluation of ozone depletion using a temperature index model
1
1
2
Diane McKnight , Christopher Jaros , Andrew M. Fountain
1
2
INSTAAR/University of Colorado, Boulder, United States, Portland State University, Portland, United
States
In McMurdo Dry Valleys (MDV) of South Victorialand, Antarctica, the temperatures rises during the
austral summer and the alpine and outlet glaciers are exposed to continuous sunlight. The resulting
meltwater flows through established channels into closed-basin lakes on the valley floors. A
temperature index approach was used to evaluate climatic drivers and hydrologic processes
underlying interannual streamflow variation. For eight streams in Fryxell Basin of Taylor Valley, we
examined a 20-year record beginning in the summer of 1990-1991 for total annual streamflow which
had been corrected for in-stream losses. This record includes five high flow summers; the largest
occurred in 2001-2002 and exceeded any previous peak flows. These high flows caused increases in
lake level of 0.5- 1 m and restructured stream and lake ecosystems due to scouring of the streambed
and mobilization of nutrients. We used a temperature correction of 7.5 °C for a temperature index
model to represent the initiation of glacial meltwater generation at below zero temperatures. We
examined the relationships between streamflow for each year of record and the summer temperature
regime, duration of the ozone hole and winter wind speed sufficient to transport sediments to glacier
surfaces. Summer temperature was found to only be a significant predictor for streamflow during the
decade preceding the first high flow season in 2001-2002. The duration of the ozone hole over the
MDV after mid-November was positively correlated with streamflow for the entire period of record at
the p=0.08 level, with a stronger relationship for the second decade of record. These results illustrate
how differences in summer climate, including the persistence of the ozone hole, can cause large
changes in meltwater generation which amplify the climate responses of the stream and lake
ecosystems in the MDV.
Page | 319
649
Measurements and modeling of atmosphere-snowpack exchange of ozone and
nitrogen oxides at Summit, Greenland and Toolik Lake, Alaska
1
2
2
3
3
3
Keenan A. Murray , Louisa J. Kramer , Claudia Toro , Brie A. Van Dam , Brian Seok , Detlev Helmig ,
4
2
5
Laurens Ganzeveld , Paul Doskey , Richard E. Honrath
1
Department of Civil and Environmental Engineering, Michigan Technological University, Houghton,
2
United States, Atmospheric Sciences Program, Michigan Technological University, Houghton, United
3
States, Institute of Arctic and Alpine Research (INSTAAR), University of Colorado at Boulder,
4
Colorado, United States, Department of Environmental Sciences, Wageningen University and
5
Research Center, Wageningen, Netherlands, Atmospheric Sciences Program, Michigan
Technological University, Deceased, United States
Snowpack is a reservoir for reactive nitrogen gases. Nitrogen oxides (NOx) are generated in the
interstitial air of sunlit snowpack through photolysis of nitrate (NO3 ) in snow. Ozone (O3) scavenged by
snowpack might react with nitrite (NO2 ) in snow and represent an additional source of NOx in
interstitial air. Gradients in NOx mixing ratios between snowpack interstitial air and the Arctic boundary
layer regulate transfer of NOx to/from snowpack and affect the O3 budget and climate at high latitude.
We collected meteorological and chemical data at Summit, Greenland and Toolik Lake, Alaska to
investigate production of NOx in snowpack over glacial ice and tundra, respectively. Semi-continuous
measurements of NO, NO2, and O3 mixing ratios were made at several depths in snowpack interstitial
air and at 2 levels above the snow surface. A one-dimensional, process-scale model of atmospheresnowpack exchange was developed to simulate profiles of NOx and O3 in the Arctic boundary layer
and in snowpack interstitial air. The model includes detailed representations of snowpack chemical
and physical processes and the physical and chemical dynamics of the overlying atmosphere that
drive atmosphere-snowpack exchange. A more highly parameterized version of the process-scale
model is incorporated into a global-scale model to assess impacts of cryosphere-atmosphere
exchange on the Arctic O3 budget.
Page | 320
C4.1d - Meteorological forcing data and distributed modelling of snow, ice and
hydrology in mountain watersheds
09.07.2013 16:15-17:45, Sanada I
1030
Numerical snow models and imperfect radiation measurements
1
1
1
Mathias Bavay , Edgar Schmucki , Charles Fierz , Michael Lehning
1
SLF, Davos Dorf, Switzerland
1
While the usage of physically based snow models is increasing in fields as diverse as catchment
hydrology, snow stability, permafrost distribution, and while an ever increasing number of
environmental parameters are monitored by more and more sophisticated networks, there are still two
distinct communities: the modelers and the experimentalists. As a consequence, the models are not
always forced with the proper data.
Unfortunately, physically based models can be very sensitive to inconsistencies in their input data,
leading the models into unphysical solutions. Using the physically-based, multi-layer, energy balance
snow model SNOWPACK, we show the impact of various strategies regarding the radiative inputs.
First, we look at the long wave radiation input that can be provided as measured incoming long wave
or parametrized incoming long wave. This is compared to the Dirichlet boundary condition, using
measured surface temperature. Then we look at the impact of the snow albedo on the simulation
outputs, using a measured albedo or using parametrizations based on the snow properties.
Page | 321
1056
Modeling in the dark: how data scarcity and uncertainty impact snowmelt
modeling
1
1
Mark Raleigh , Jessica D. Lundquist
1
Civil and Environmental Engineering, University of Washington, Seattle, United States
When modeling seasonal snow in mountainous catchments, it is typical that the driving data required
to run a snow model are not observed at the locations of interest, and instead are estimated
empirically from other variables or extrapolated from measurements at distant sites. Uncertainty in
these simulated data inputs will propagate through the model in unknown ways and increase the
uncertainty in model outputs (e.g., snow depth, water equivalent, and melt). Here we attempt to
quantify the impact of forcing data availability and empirical data estimation on uncertainties in
physically-based snow modeling. Results are presented from controlled experiments using the 1dimensional, multi-layer SNTHERM model at a mid-elevation (1325 m) site at Col de Porte
(Chartreuse Range, France) and high-elevation sites (3370 m, 3720 m) at the Senator Beck Basin
(Rocky Mountains, USA), where multiple years of all required forcing variables (e.g., radiation,
temperature, humidity, wind, and precipitation) are measured locally to drive the model. A suite of data
availability scenarios are considered: (1) assuming all forcing data are available at hourly resolution,
(2) assuming some combination of forcing parameters are available, and (3) assuming only daily air
temperature and precipitation are available. As we deprive the model of different variables, we replace
them with estimates from typical empirical approaches to examine how uncertainty in modeled SWE
and snowmelt change with data approximations. Results indicate that uncertainty in radiation has a
significant impact on model accuracy, and uncertainty in the phase of hourly precipitation can be
significant at lower elevation sites. The results also illustrate the difficulty in isolating forcing data
uncertainty from additional uncertainties in model parameterizations and verification data. The goal of
these experiments is to better understand which variables require improved representation or more
observations in mountainous catchments for the purposes of snowmelt modeling.
Page | 322
1113
Resilience in energy balance snowmelt modelling
1
1
2
3
Christopher Marsh , John W. Pomeroy , Raymond Spiteri , Howard Wheater
1
2
Centre for Hydrology, University of Saskatchewan, Saskatoon, Canada, Computer Science,
3
University of Saskatchewan, Saskatoon, Canada, Global Institute for Water Security, University of
Saskatchewan, Saskatoon, Canada
In many parts of the world, the snowmelt energy balance is dominated by net solar shortwave
radiation. This is the case in the Canadian Rocky Mountains, where clear skies dominate the winter
and spring. In mountainous regions, irradiance at the snow surface is not only affected by solar
angles, atmospheric transmittance, and the slope and aspect of immediate topography, but also by
horizon-shadows, i.e., shadows from surrounding terrain. Many hydrological models do not consider
such horizon-shadows and the accumulation of errors in estimating solar irradiance by neglecting
horizon-shadows may lead to significant errors in calculating the timing and rate of snowmelt due to
the seasonal storage of internal energy in the snowpack.
An unstructured triangular-mesh-based horizon-shading model is applied to the Marmot Creek
Research Basin (MCRB), Alberta, Canada. The horizon-shadow model was run at a point scale at
three sites throughout the MCRB. These irradiance data were used with a coupled energy and mass
balance snowmelt model (SNOBAL, via The Cold Regions Hydrological Model, an HRU-based
hydrologic model) to investigate the effects of shading on snowmelt timing. It was observed that the
energy balance model was reasonably insensitive to errors in incoming shortwave radiation due to the
self-balancing nature of the energy balance. Small spatial-scale surface flux feedbacks were
observed. Due to the limited incoming shortwave radiation associated with shaded conditions, the
snowpack remained cooler, resulting in lower longwave radiation loss and an increased sensible heat
flux. Such feedbacks demonstrate insensitivity to input errors, and this insensitivity is important for
modelling in areas with poor quality data as well determining the model complexity required to
calculate melt rates.
Page | 323
1044
Set up and evaluation of distributed and semi-distributed simulations using
SURFEX/ISBA-Crocus in the partly glacierized Arve-Mont-Blanc catchment at
Chamonix, France
1
1
1
1
1
Matthieu Lafaysse , Samuel Morin , Marie Dumont , Alexandre Wegiel , Luc Charrois , Antoine
2
Rabatel
1
2
CNRM-GAME/CEN Météo-France/CNRS, Saint Martin d'Hères, France, LGGE (CNRS/UJF),
Grenoble, France
The detailed snowpack model Crocus has until now been operationally used for avalanche hazard
warning in the French mountains. Numerical simulations have traditionally been carried out for a range
of altitudes, slopes and aspects to inform avalanche forecasters on the main characteristics of the
snowpack. Further research applications have proven that such detailed snowpack models are also
relevant in the context of glacier mass balance studies and mountain hydrology. Here we present a
novel implementation of Crocus, now incorporated in the common Earth surface platform “SURFEX” of
Météo-France as one of the snowpack schemes of the land surface model ISBA. This allows to run
this model in a wider range of scientific contexts and in particular the numerical simulation of several
key compartments of the mountain cryosphere environment, including snow, glaciers, moraine and
vegetation.
In this presentation, a set of simulations using SAFRAN meteorological fields will be presented to
demonstrate the expected capabilities of this modelling framework. The results of a fully distributed
version of the model over the Arve-Mont-Blanc basin (200 km²) will be evaluated against point scale
snow measurements, glacier mass balance data from the GLACIOCLIM observatory, satellite snow
cover information and river flow at the outlet of the watershed. These results will be compared to
numerical simulations carried out in a semi-distributed manner, whereby areas of homogeneous slope,
altitude and aspect are treated together and aggregated prior to further downstream simulations,
thereby limiting numerical costs but ignoring the effect of shadows by surrounding mountains.
This work is carried out within a long-term objective of improving the spatial resolution and overall
performance in mountainous terrain of this physically-based land surface model. Longer term
perspectives include the use of high resolution forecasts from state-of-the-art numerical weather
prediction models, for operational avalanche and floods warning applications.
Page | 324
692
Simulating snow distribution and melt in alpine and forested terrain
1
1
Keith Musselman , John Pomeroy
1
Centre for Hydrology, University of Saskatchewan, Saskatoon, Canada
A physically based snowmelt model coupled to a blowing snow module forced with output from a CFD
windflow model was tested within the framework of the Cold Regions Hydrological Model (CRHM). It
2
was applied at high resolution to simulate the dominant snow processes in the 9.7 km Marmot Creek
basin, Alberta, Canada. The land cover is characterized as alpine (33%), sparsely forested treeline
(10%), densely forested (53%), and forest clearing (4%). The effects of small-scale variations in
surface roughness and forest cover were included in the CFD model to produce near-surface windflow
maps under a range of prescribed wind conditions. Reasonable agreement with wind measurements
from 8 automated stations was obtained. Snow transport and blowing-snow sublimation was simulated
with the Distributed Blowing Snow Model (DBSM) and the snow losses or gains were subsequently
adjusted within the snowmelt model. Compared to measurements from airborne LiDAR, snow surveys,
and automated snow depth sensors, the model system represented the dominant snow distribution
features in Marmot Creek. In the alpine, snow distribution was largely governed by wind scour,
sublimation and redistribution. High snow accumulation was simulated at treeline as a result of abrupt
wind speed reductions and increased deposition, but the process was sensitive to changes in wind
speed and direction and the representation of forest roughness heights. The middle and lower
elevations were largely uninfluenced by snow transport processes. The results highlight the utility of a
CFD model to simulate realistic windflow patterns in complex terrain where wind strongly influences <
50% of the basin area but as much as 75% of the basin SWE. Limitations of the turbulence model
include the simulation of flow separation on the lee side of steep ridgelines, steady-state assumptions,
and the representation of wind dynamics in areas of sparse forest structure and significant upwind
fetch (i.e. treeline).
Page | 325
289
The NASA/JPL airborne snow observatory: imaging spectrometer and LiDAR
for coincident retrieval of snow albedo and snow water equivalent
1
2
3
4
5
Thomas Painter , Joseph Boardman , Jeffrey S. Deems , Frank Gehrke , Cate Heneghan , Bruce
6
5
5
5
McGurk , Felix Seidel , Amy Trangsrud , Kostas Andreadis
1
2
California Institute of Technology, Jet Propulsion Laboratory, Pasadena, United States, Analytical
3
Imaging and Geophysics, Boulder, United States, National Snow and Ice Data Center, Boulder,
4
5
United States, California Department of Water Resources, Sacramento, United States, Jet
6
Propulsion Laboratory, Pasadena, United States, McGurk Hydrologic, Orinda, United States
Snow cover and its melt dominate regional climate and water resources in many of the world's
mountainous regions. However, we face significant water resource challenges due to the intersection
of increasing demand from population growth and changes in runoff total and timing due to climate
change. Moreover, increasing temperatures in desert systems will increase dust loading to mountain
snow cover, thus reducing the snow cover albedo and accelerating snowmelt runoff.
The two most critical properties for understanding snowmelt runoff and timing are the spatial and
temporal distributions of snow water equivalent (SWE) and snow albedo. Despite their importance in
controlling volume and timing of runoff, snowpack albedo and SWE are still poorly quantified in the US
and not at all in most of the globe, leaving runoff models poorly constrained.
Recognizing this need, JPL developed the Airborne Snow Observatory (ASO), an imaging
spectrometer and imaging LiDAR system, to quantify snow water equivalent and snow albedo, provide
unprecedented knowledge of snow properties, and provide complete, robust inputs to snowmelt runoff
models, water management models, and systems of the future.
The ASO will be evaluated during a multi-year Demonstration Mission of weekly acquisitions in each of
the Uncompahgre River Basin (Upper Colorado) and the Tuolumne River Basin (Sierra Nevada)
beginning in spring 2013. The ASO data will be used to constrain spatially distributed models of
varying complexities and integrated into the operations of the O'Shaughnessy Dam on the Hetch
Hetchy reservoir on the Tuolumne River. Here we present the first results from the ASO
Demonstration Mission 1 along with modeling results with and without the constraint by the ASO's high
spatial resolution and spatially complete acquisitions. ASO ultimately provides foundation for coming
spaceborne missions.
Page | 326
B4.1d - Global monsoon system: past, present and future
09.07.2013 16:15-17:45, Aspen I
766
Distinguished ENSO response and moisture supply of dominant intraseasonal
modes in the East Asian summer monsoon
1
1
1
Kyung-Ja Ha , Hyoeun Oh , Jung-Eun Chu
1
Pusan National University, Busan, Korea, Republic of
On the basis of various self-organizing map (SOM) analysis, a kind of artificial neural network, the
dominant modes of the East Asian summer monsoon (EASM) are identified as the Meiyu-Baiu,
Changma, post-Changma, and the dry-spell modes. The SOM approach supposes that sudden phase
change during summer monsoon period results from the presence of non-linear coupled features of
intraseasonal phases. Thus, the origin and nature of the moisture supply in the dominant
intraseasonal modes of the EASM rainfall can be identified in terms of each mode. To discuss the
uniqueness of EASM major modes, the horizontal and vertical moisture supply are examined using
moisture budget equation consisting of convergence, advection and transient eddy terms. Strong
moisture convergence region can be found over the southern part of Meiyu-Baiu rainband. The
Changma mode has zonal-oriented moisture source which confined to low-level from surface to 925hPa over the Korean peninsula. Furthermore, convective instability deeply developed in the Changma
mode. It means advection of moist, warm air by low-level wind from the south and cold, dry air from
the north are fundamental for generating convective instability and sustaining convective activity. On
the contrary to Changma mode, post-Changma mode has meridional-oriented moisture source with its
deep vertical profile. Moisture divergence regions cover the northern China, Korea, and Japan for dryspell mode. Besides the moisture convergence and advection, the transient eddies play a role in
supplying moisture over the boundary region of mean flow. It is demonstrated that a strong modulation
of the Changma and dry-spell modes on interannual time scales occurs during El Nino and La Nina
years, showing asymmetric ENSO response. The evidence of relationship between tropical SST,
western North Pacific anticyclone, easterly vertical wind shear, and extratropical intraseasonal phases
has been emphasized.
Page | 327
527
The extremely strong Western North Pacific High in boreal summer 2010:
impacts and causes
1
2
Huang-Hsiung Hsu , Chi-Cherng Hong
1
Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan, Republic of China,
2
Taipei Municipal University of Education, Taipei, Taiwan, Republic of China
Whereas La Niña in 2010 was moderate, the associated Western North Pacific subtropical high
(WNPSH) during boreal summer was extremely strong and exhibited an unusual northward and
westward expansion, which resulted in an extremely few tropical cyclone (TC) genesis (with significant
westward shift) in the WNP and extreme warm and dry conditions in Northeast Asia. Data analysis and
numerical experiments were used to investigate the roles of sea surface temperature anomalies
(SSTA) in various basins, particularly the record-breaking warm SST in the tropical and extratropical
Atlantic in contributing to the unusual WNPSH.
It shows that, in addition to the Gill-type anticyclonic response to the cold SST in the equatorial central
Pacific, which partially explains the enhancement of the WNPSH, the warm SST in the North Indian
Ocean (IO)/tropical Atlantic (TA) forced local/remote vertical overturning circulation, which in turn
caused the enhancement and westward expansion of the WNPSH. In addition, the warm SST in the
north Atlantic (NA) also affected the WNPSH in a different from way from the tropical SST. The
numerical experiment, consistent with the observation, reveals that the NA-SST induced extratropical
wave-like disturbances that propagated downstream and resulted a barotropic anticyclonic anomaly in
the WNP north of the expected position of the WNPSH. This suggests that the strong downstreampropagating wave activity contributed to the northward shift of the WNPH anticyclone in summer 2010.
Page | 328
1266
Interannual variability of East Asian summer monsoon simulated by CMIP3 and
CMIP5 AGCMs
1
2
2
Tianjun Zhou , Fengfei Song , Guangqing Zhou
1
2
LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China, Institute of
Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
The inter-annual variability of East Asian Summer Monsoon (EASM) are simulated by 13 CMIP3 and
19 CMIP5 AGCMs. Climatology of 850 hPa wind representing monsoon circulation is reasonably
reproduced in the multi-model ensemble (MME) of CMIP3 and CMIP5 AGCMs except with a
northward shift of the western Pacific subtropical high (WPSH). But the monsoon rainband known as
Meiyu/baiu/changma rainfall band are poorly simulated. Improvement is seen from CMIP3 to CMIP5,
as evidenced by the pattern correlation of precipitation, which is 0.76 (0.80) for MME of CMIP3
(CMIP5). A better simulation of monsoon circulation corresponds to a better simulation of monsoon
rainfall. Both CMIP3 and CMIP5 MME well reproduce the inter-annual variability of EASM.
Correlations of monsoon index between the observations and the MME mean reaches 0.70(0.66) for
CMIP3 (CMIP5). The observed inter-annual variability mode features an anticyclone over the
northwestern Pacific, which is associated with deficient rainfall in the western Pacific but excessive
rainfall along the Yangtze River (30°N) as a dipole mode. Above features are partly reproduced in
CMIP3 and CMIP5 MME but with two main deficiencies: weaker precipitation anomalies and
southward shift of the dipole rainfall pattern. These deficiencies are closely related to the weak and
southward shift of western Pacific anticyclone (WPAC). The skill score of the inter-annual variability
pattern has improved from 0.33 in CMIP3 MME to 0.40 in CMIP5 MME. Analyses demonstrate that the
north Indian Ocean (NIO) rainfall response to the tropical Indian Ocean warming and the following
Kelvin wave response are vital to the establishment of WPAC. A successful reproduction of EASM
inter-annual variability mode depends highly on this kind of Indian Ocean-western Pacific teleconnection mode. Improvement is seen from CMIP3 to CMIP5 due to a better reproduction of the
Indian Ocean-western Pacific tele-connection mode in CMIP5.
Page | 329
556
Interdecadal variability of Western North Pacific summer monsoon through the
Pacific-Japan (PJ) pattern
1
2
2
Hisayuki Kubota , Yu Kosaka , Shang-Ping Xie
1
2
JAMSTEC, Yokosuka, Japan, Univ. of California, San Diego, San Diego, United States
The Pacific-Japan (PJ) pattern is a major pressure pattern of Asian summer monsoon over the
Western North Pacific and characterized by anomalous circulation between tropical convections over
the Philippine Sea and anticyclones over the midlatitude over the east of Japan. The long-term index
for PJ pattern was defined by using station data and reproduced the PJ pattern from 1897 to 2012. We
chose two stations in Yokohama of Japan and in Hengchun of Taiwan respectively in the positive and
negative part according to the first mode of EOF SLP correlation distribution. The correlation between
PJ pattern index and preceding winter ENSO and summer Indian Ocean SST is significantly high. The
positive (negative) PJ pattern follows by La Niña (El Niño) and is based on the Indian Ocean capacitor
effect. During the positive phase of PJ pattern, Western North Pacific summer monsoon activity is
intensified including tropical cyclone activity and produces a lot of rain in Asian summer monsoon
region and dry hot summer in Japan, Korea and Yangtze river basin of China. The 116-year time
series of PJ pattern index demonstrates that we can divide into two periods when the variance of
ENSO and PJ pattern index are high and the correlation between ENSO and PJ pattern index is
dominant after 1970s and before 1910s, and low correlation between ENSO and PJ pattern index and
small variances during 1920s to 1970s. Interdecadal modulation of ENSO teleconnection may
influence the strength of the PJ pattern index through Indian Ocean capacitor effect. The long-term
index of PJ pattern demonstrates that climate variability associated with ENSO regime shift will be the
dominant variability than the global warming.
Page | 330
46
The comparison of intraseasonal oscillation features between southwest
monsoon of the Bay of Bengal and South China Sea summer monsoon
1
Ting Li
1
State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid
Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
Adopting NCAR/NCEP reanalysis data and APHRO_MA_V1003R1 precipitation data, filtering summer
monsoon index Im in 30-60d and averaging in the Bay of Bengal (BOB) and the South China Sea
(SCS) respectively to present the Intraseasonal Oscillation (ISO) of Southwest Monsoon of BOB
(BOBSM) and SCS Summer Monsoon (SCSSM), and to compare their ISO features. ISO of both the
two monsoons has 3 and a half ISO waves during summer monsoon period (May-Oct). Along the zone
of Arab Sea-Western Pacific Ocean, there are 4 eastward propagations of ISO from Arabian Sea and
3 westward propagations from western Pacific Ocean. After Jul, westward propagation of ISO is
inhabited and eastward propagation can arrive to western Pacific Ocean. At the same time, there are 4
meridional ISO propagations. In BOB, it contains northward propagation from Tropic eastern Indian
Ocean in south of 15°N, and southward propagation of sub-tropical monsoon ISO in north of 15°N.
Otherwise, in SCS, it is just northward propagation from Tropic. In 6 phases of ISO of BOBSM and
SCSSM respectively, there is opposite-phase feature in low frequency (LF) circulation and convection
in phase 1-3 and 4-6, caused by eastward and northward movement of ISO in Tropic eastern Indian
Ocean. LF convection propagates along southwest-northeast direction from Tropic eastern Indian
Ocean to BOB (needing about 14d), exciting the ISO of BOBSM, and then eastward propagates to
SCS (6d), exciting the ISO of SCSSM, at last propagates to South China (25d), forming the meridional
and zonal relay propagation of ISO from Tropic Indian Ocean propagates to South China (45d). The
precipitation belt impacted by BOBSM moves eastward with LF convection in south of 20°N, but the
precipitation belt impacted by SCSSM, not only as above, but also moves northward with LF
convection of SCS in north of 20°N.
Page | 331
PS-2 - Poster session Tuesday
09.07.2013 14:45-16:15, Foyer
TU-01_A3.2
The anomalous circulation over Asia in winter and it associated with the
precursors both of SST and sea ice
1
Qingyun Zhang
1
Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), Beijing, China
The clod or warm winter occurred are dependent on the varying background circulation in wintertime.
Therefore, the variation of monthly mean temperature over Northeast China during midwinter
(January) and associated circulation anomalies as well as some precursors on multiple time scales
were studied. The homogenized daily mean temperature during 1960-2008 covering whole China with
549 situ stations from China Meteorological Administration 、NCEP/NCAR reanalysis dataset、Sea
Surface Temperatures （SST） and the Sea Ice Concentration (SIC) data from Hadley center are
used in the study. The large-scale atmospheric circulation characteristics of January temperature
anomaly cases in Northeast China during 1960-2008 and precursory oceanic conditions are analyzed.
The January monthly-mean surface air temperature (SAT) anomalies and duration days of low
temperature in midwinter are used in order to define temperature anomaly cases. The anomalous
cyclonic circulation over the northeast Asia strengthened the northerly flow in midwinter for cold cases,
the anomalous anticyclonic circulation over the northeast Asia weakened the northerly flow in
midwinter for warm cases. The negative (positive) SSTA appeared in Northwestern Pacific, and sea
ice concentration in the Barents-Kara seas increased (decreased) in December are probably linked to
the cyclonic (anticyclonic) circulation pattern over the Northeast Asia in midwinter for cold (warm)
cases. There exist strong relationships between SSTA in (150-180E，30-50N) and the SAT in
Northeast China during annual time scale. The sea ice concentration more closely related to SAT in
Northeast China during decadal time scale. The SST plays more important roles in the inter-annual
variation of SAT in northeast China, and the SIC plays more important roles in the decadal variation of
SAT in northeast China.
Page | 332
TU-02_A3.2
Effect of multi-decadal-scale variation in Okhotsk High on fog frequency over
the Pacific side of the Hokkaido Island, Japan
1
1
Shiori Sugimoto , Tomonori Sato
1
Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Japan
Sea fog, which is frequently observed over the cold Oyashio current in the North Pacific during
summer, often migrates into the Pacific side of Hokkaido Island, northern Japan and affects human
activities due to high fog frequency. The long-term variation in summer fog frequency is examined at
three observatories in the Pacific side of Hokkaido Island, i.e., Nemuro, Muroran, and Tomakomai.
Obvious multi-decadal-scale variation is confirmed in fog frequency at all observatories and it is similar
among three sites after late 1970s with high/low fog frequency period during 1981-1990/1994-2003,
although Nemuro observatory is located approximately 400 km eastward from other two observatories.
This result suggests that multi-decadal-scale fog frequency fluctuation in these sites is under the
strong control of similar synoptic-scale forcing. To identify synoptic-scale factors controlling fog
frequency multi-decadal-scale variation in these regions, large-scale circulation pattern covering
southern Hokkaido Island and sea surface temperature variation around the northern Japan are
analyzed by using atmospheric and oceanic reanalysis datasets. For high fog frequency period,
anomalous southeasterly wind, which is favorable for sea fog advection from the ocean to land,
prevails over the Pacific side of Hokkaido Island due to intensification and southward extension of the
Okhotsk High. The Okhotsk High behavior is strongly related with fluctuation of sea surface
temperature around the Sea of Okhotsk. We suggest that the multi-decadal-scale fog frequency
variation over the Pacific side of Hokkaido Island is affected by the atmospheric circulation change
associated with oceanic multi-decadal-scale variation.
Page | 333
TU-03_A3.2
The roles of El Niño Modoki and North Atlantic Oscillation in the severe
drought in Southwest China during winter 2009/2010
1
1
Hongjian Tan , Rongshuo Cai
1
Key Laboratory of Global Change and Marine-Atmospheric Chemistry, Third Institute of
Oceanography, State Oceanic Administration, Xiamen, China
The Southwest China suffered from an extreme drought event in the boreal winter of 2009/2010, while
the sea surface temperature anomalies (SSTAs) in global ocean presented distinct conditions. A
series of numerical experiments were conducted with an AGCM to investigate the separate and
common effects of SSTAs in different parts of global ocean on this event. The model could reproduce
the large rainfall deficits in Southwest China forced by the observational global SST during the same
period. The simulated results indicated that the El Niño Modoki and North Atlantic Oscillation (NAO)
had obvious effect on the severe drought in Southwest China and South Asia, which were also
examined by using the daily data of precipitation at 756 stations in China, GPCP monthly precipitation
dataset and NCEP/NCAR reanalysis datasets. Particularly, the simulated results also indicated that
atmospheric circulation anomalies induced by El Niño Modoki and NAO, e.g., the descending branch
of the western Walker cell associated with the El Niño Modoki might suppress the local convective
motion, resulting in the persistent drought in Southwest China. Consequently, in this study, it is
suggested that El Niño Modoki and North Atlantic Oscillation (NAO) may play key roles in the severe
drought in Southwest China during the boreal winter of 2009/2010.
Page | 334
TU-04_A3.2
Variability and long-term trends of the wintertime precipitation in China during
1979-2010
1
2
Tongmei Wang , Qigang Wu
1
2
Department of Atmospheric Sciences, Sun Yat-sen University, Guangzhou, China, School of
Atmospheric Sciences, Nanjing University, Nanjing, China
With observed station precipitation data in China, a gauge-based analysis of daily precipitation over
East Asia, the ERA-Interim reanalysis data and the simulations of CMIP5 models, we investigate the
interannual variability and the long-term trends of wintertime precipitation in China and over East Asia
in this study. It is shown that China has experienced a decreased precipitation trend in its Southern
part and increased trend in Yangtze-Huaihe river basin since 1979.
EOF analysis of wintertime precipitation field shows that the leading EOF (EOF1) is characterized by
the uniformly enhanced rainfall over the Southern China, without obvious long-term trend in the
corresponding PC time series. The second EOF mode (EOF2) is represented by meridionally banded
dipole-like structure with the more (less) precipitation changing over the Yangtze River Basin (the
South China), with significant trend in its PC time series (about 1.27mm/30yr, which is significant at
the 5% level). SVD analysis between precipitation in China and SST in the tropics shows that the
EOF1-like precipitation variability in China is closely related to the traditional ENSO-like SST forcing in
the tropical Indo-Pacific basins, while dipole-like EOF2 precipitation variability in China is associated
with the SST anomalies in the western-central Pacific. This indicates that the equatorial westerncentral Pacific SST warming in the past decades might have contributed to the long-term trends of
precipitation in China. Based on the simulated results of the AMIP and Historical runs from CMIP5
Models, we find several GCMs have reasonably reproduced long-term trends of wintertime
precipitation in China. Our preliminary results suggest that both SST forcing and external
anthropogenic forcing associated with increasing greenhouse gas concentration are important factors
that have lead to long-term changes of wintertime precipitation in China in the past decades.
Page | 335
TU-06_A3.2
Interdecadal variability of the Baiu precipitation in the western North Pacific
1,2
3
2
Tomohiko Tomita , Bunmei Taguchi , Koutarou Takaya
1
2
Graduate School of Science and Technology, Kumamoto University, Kumamoto, Japan, Research
3
Institute for Global Change, JAMSTEC, Yokohama, Japan, Earth Simulator Center, JAMSTEC,
Yokohama, Japan
In early boreal summer (June), the Baiu front, which is also called the Mei-Yu front in China, is located
along a boundary between the subtropics and the extratropics in the western North Pacific near
Japan. In its frontal activity, an interdecadal change was detected around 1990, which is characterized
by larger amount of precipitation in 1990´s than in 1980´s and by anomalous upward surface heat
fluxes with positive sea surface temperature (SST) anomalies in the Baiu/Kuroshio (B/K) region in
1990´s. This interdecadal change was locally forced by the oceanic Pacific Decadal Oscillation, whose
signals were submerged under the seasonal thermocline in boreal summer in most of the North Pacific
except for the B/K region. To generalize the above physical processes established by a case of 1990,
this work extended the analysis using a 150-year control integration of a coupled GCM. On
interdecadal time scales, a significant positive correlation was confirmed between simulated SST and
precipitation in the B/K region. In decades when the positive precipitation anomalies appeared in this
region, the upward surface heat fluxes were anomalously large over positive SST anomalies. The
close inspection further revealed that there was a specific phase relationship in anomalies of SST,
precipitation, and surface heat fluxes. The anomalies of SST and surface heat fluxes are almost
coherent in the northern part of precipitation anomalies. This systematic spatial phase difference
implies that the surface air-sea interaction leads a specific interdecadal modulation of the Baiu
precipitation during the seasonal northward migration of the front.
Page | 336
TU-10_A3.3
Northern Hemisphere atmospheric circulation according to classification by
B.L. Dzerdzeevskii
1
Nina Kononova
1
Institute of Geography, Moscow, Russian Federation
The long-term series of fluctuation of monthly and annual Northern Hemisphere atmospheric
circulation from 1899 till 2012 according to Dzerdzeevskii classification have been considered. The
differences of character of atmospheric circulation between circulation epochs have been revealed.
The circulation and climatic characteristics of extreme decades of circulation epochs in the Northern
Hemisphere and its six sectors - Atlantic, European, Siberian, Far East, Pacific and American - are
presented. The main feature of the period from 1981 to 1998 is the increase in the frequency (number
of cases) and duration (number of days) of southern meridional group circulation, and period 19992012 can be characterized by the increase in the frequency and duration of northern meridional group
circulation.
Dzerdzeevskii's classification includes 41 elementary circulation mechanism (ECM). Every ECM has a
dynamic scheme, so it characterizes the entire Hemisphere and at the same time show the trajectory
of cyclones and anticyclones over specific regions. Each ECM applies to certain seasons. Therefore
this classification has been used for the study of global and regional climate changes, fluctuation of
atmosphere - ocean system, and snow and ice regime.
Till recently the study of long-term fluctuations of atmospheric circulation, air temperatures and
precipitation has pointed their coordination in different sectors of the Hemisphere. Research of the
displacement of the border between Low and High over the Hemisphere at the same ECM during
different circulation periods was started
The purpose of this paper is to show results of the researches of long-term fluctuations of the Northern
Hemisphere atmospheric circulation for 1899-2012 according to the classification by B.L.
Dzerdzeevskii and their manifestation in a climate of Northern Hemisphere and different regions.
Page | 337
TU-11_A3.3
Using modal decomposition to study beating patterns of solar cycle data
1
2
2
3
Eleanor Williamson , Mausumi Dikpati , Nicholas Featherstone , Charles Lindsey
1
2
Physics, Lawrence University, Appleton, United States, High Altitude Observatory, Boulder, United
3
States, NWRA, Boulder, United States
A better predictive ability of space weather, both past and future, could provide a better understanding
of the earth's climate. One path to this is through a deeper comprehension of the solar cycle. The
periodic appearance and equator-ward migration of sunspots on the solar surface, the telltale sign of
the 22-year solar cycle, is a process that does not operate symmetrically between the northern and
southern hemispheres. We characterize the similarities and differences between the two hemispheres
using a Fourier modal decomposition of the sunspot area record for each cycle. For this purpose we
use long-term spot area data available since 1878. Our goals are first to see how well the individual
cycle shapes can be described in terms of a few modes, second to characterize the asymmetries and
symmetries between different hemispheres in terms of the interference of these individual modes, and
third to establish whether or not any long term trends are evident when the data is viewed in this way.
More specifically, we are interested in trends that might aid in the development of predictive capability
for future cycles. We analyze the resulting amplitudes and phase shifts between cycles and
hemispheres and find that individual cycles can be well represented by as few as 5 modes. Cycles
with a high maximum total area tend to have a large variation in strength of harmonics, and
correspondingly cycles with a small maximum total area tend to have little variation in strength of
harmonics. A large difference between the amplitude of the fundamental mode in the north and south
does not necessarily correspond to a large difference between north and south at higher harmonics.
Page | 338
TU-12_A3.3
Influences of external forcing changes on the summer cooling trend over East
Asia
1
Bian He
1
IAP, Beijing, China
Observations indicate a surface cooling trend during the East Asian summer in recent decades,
against a background of global warming. This cooling trend is re-examined using station data from
1951 to 2007, and atmospheric general circulation model (AGCM) simulations are performed to
investigate the possible influence of changes in external forcing. The numerical experiments are
designed to investigate the effects of four types of external forcing: greenhouse gases (GHGs), Total
Solar Irradiance (TSI), ozone, and the direct effects of aerosols.
Results indicate that external forcing contributes to the cooling trend over East Asia. Furthermore,
GHGs, and to a lesser degree the direct effects of aerosols, are the main contributors to the cooling
trend. The possible linkages between the external forcings and the cooling trend are discussed.
Page | 339
TU-13_A3.3
Prediction of decadal variability of sea surface temperature by a coupled global
climate model FGOALS_gl developed in LASG/IAP
1
Bo Wu
1
Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), Beijing, China
A decadal climate prediction is performed by a coupled global climate model FGOALS_gl developed in
the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid
Dynamics (LASG) at the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences.
Firstly, an Incremental Analysis Updates (IAU) scheme is applied to assimilate surface and subsurface
ocean temperature and salinity fields derived from an oceanic objective analysis data for the
initialization of the model ocean component. Started from the initialized states, hindcast integrations
are performed with the specified historical solar cycle variations, concentrations of green house gas
and sulphate aerosol, following standard 20C3M scenario used in the phase 3 of the Coupled Model
Intercomparison Project (CMIP3). Based on the hindcast integrations, we perform forecast integrations
under the radiative forcing of the A1B scenario in the CMIP3. Compared with the 20C3M run, the
hindcast integrations have much higher skills in simulating the decadal variability of SST in the tropical
central-eastern Pacific and mid-latitude northeastern Pacific, suggesting that the ocean initialization is
able to enhance the model skill in the regions with large decadal variability. The forecast integrations
suggest that the SST in the tropical central-eastern Pacific has reached its trough phase and will
gradually increase in the following 10-15 years. Meanwhile, the global mean surface temperature
predicted by the forecast integrations increases slower than that projected by the A1B scenario run
over 2000-2010, but faster than the latter after that.
Page | 340
TU-14_A3.3
Ground-based aerosol optical depth climatology and trends at baseline GAWPFR stations from 1999 - 2011
1
2
1
1
1
Stephan Nyeki , Christos Halios , Julian Gröbner , Natalia Kouremeti , Christoph Wehrli
1
2
PMOD/WRC, Davos, Switzerland, Dept. Meteorology, University Reading, Reading, United Kingdom
Accurate and long-term measurements of aerosol optical depth (AOD) serve as an important
contribution to studies assessing the effect of aerosols on the Earth's radiation budget. Although
satellites are being increasingly used to monitor AOD on a global scale, ground-based measurements
at baseline stations representative of regional background values are still essential for validation and
calibration purposes.
In order to monitor spectral AOD over the long-term and provide data of traceable quality, the GAWPFR AOD network (World Radiation Centre, Davos) was established by the WMO Global Atmosphere
Watch (GAW) programme. Several existing GAW baseline stations were chosen for the deployment of
Precision Filter Radiometers (PFR; 368, 412, 500 and 862 nm; WRC manufacture) to measure AOD.
Stations for which a 10-year time-series exists include: Alice Springs (547 m asl, Australia), Bratts
Lake (576 m, Canada), Izana, (2371 m, Tenerife, Spain), Jungfraujoch (3580 m, Switzerland), Mace
Head (20 m, Ireland), Mauna Loa (3397 m, Hawaii, USA), and Ny Alesund (17 m, Svalbard, Norway).
Quality controlled and assured AOD data from this GAW-PFR network are submitted to the World
Data Centre for Aerosols (WDCA; www.gaw-wdca.org) which acts as a central portal for data
collection and dissemination activities.
This study will discuss the AOD climatologies and present a trend analysis at the above sites.
Page | 341
TU-15_A3.3
The effects of stratosphere-troposphere coupling on the decadal predictability
of the climate system
1,2
1
3
1
Miriam D'Errico , Alessio Bellucci , Chiara Cagnazzo , Silvio Gualdi
1
2
CMCC Euro-Mediterranean Centre for Climate Change, Bologna, Italy, University of Venice, Venice,
3
Italy, ISAC-CNR, Rome, Italy
The coupled ocean-atmosphere CMCC-CMS model is used to investigate the influence of the
stratosphere on the decadal predictability. As part of the EU-funded COMBINE Project, a set of
decadal prediction experiments are performed for the 1960-2005 period, following the CMIP5 protocol
using historical radiative forcing conditions, followed by RCP4.5 scenario settings from 2006 onward.
The decadal predictions consist in 3-member ensembles of 10-year simulations starting at 5-year
intervals, with the ocean initial states provided by ocean reanalyses differing by assimilation methods
and assimilated data. A purpose of this work is to asses the impact of the initialization to reproduce
climate variations with respect to an uninitialized climate simulation performed for the same time
period of the predictions using identical forcing conditions.
Focus will be also laid on the differences between simulations by high-top configuration (CMCCCMS), including a well-resolved stratosphere and equivalent simulations using a low top model
differing only in vertical extent and vertical resolution, to estimate how the inclusion of a wellrepresented stratosphere could impact climate predictability on the decadal time scale.
Page | 342
TU-16_A3.3
Greenhouse warming and solar brightening in and around the Alps
1
Rolf Philipona
1
Federal Office of Meteorology and Climatology MeteoSwiss, Aerological Station, Payerne,
Switzerland
At low elevations (500 m a.s.l.) central Europe's surface temperature increased about 1.3°C since
1981. Interestingly, at high elevations (2200 m a.s.l.) in the Alps, temperature rose less than 1°C over
the same period. Detailed investigations of temperature, humidity and the radiation budget at lowland
and alpine climate stations now show that the difference in temperature rise is likely related to unequal
solar- and greenhouse warming. The analysis shows that the important decline of anthropogenic
aerosols in Europe since the mid 1980s led to solar brightening at low elevations, whereas inherent
low aerosol concentrations at high elevations led to only minor changes of solar radiation in the Alps.
-1
In the Lowland absolute humidity and also total net radiation show an about 6 % K ClausiusClapeyron conform increase with temperature since the 1980s. In the Alps however, the percentage
increase rate of humidity and total net radiation is more than twice as large. This large water vapour
increase in the Alps is likely related to strong warming and thermal advection in the Lowlands, and
may also have increased due to atmospheric circulation changes. Hence, while in the Alps
temperature increased primarily due to strong water vapour enhanced greenhouse warming, solar
brightening combined with anthropogenic greenhouse gas and water vapour feedback greenhouse
warming led to a higher temperature increase at low elevations in Central Europe.
References:
Philipona, R. 2012: Greenhouse warming and solar brightening in and around the Alps. Int. J. Climatol.
DOI: 10.1002/joc.3531.
Page | 343
TU-17_A3.3
Trends In surface radiation and cloud radiative effect over Switzerland in the
past 15 years
1
1
2
Stefan Wacker , Julian Gröbner , Laurent Vuilleumier
1
2
PMOD/WRC, Davos Dorf, Switzerland, Meteo Swiss, Payerne, Switzerland
Down-welling short-wave and long-wave radiation are key components in the surface radiation budget
and hence accurate monitoring is essential in order to address climate-relevant issues. Clouds
substantially modify the radiation budget by reflecting short-wave and emitting long-wave radiation.
Thus, they play a crucial role in the climate system.
We analyzed 15 years (1996-2010) of high quality observations of surface down-welling short-wave
and long-wave radiation from four Swiss sites: The lowland stations at Payerne and Locarno-Monti
located North and South of the Alps, respectively; Davos, and the High Alpine Station Jungfraujoch.
-2
Down-welling short-wave radiation at Locarno-Monti has significantly increased by 9 Wm in the 19962010 period, whereas no significant trends at the 95 % confidence level are observed at the other
three stations. In addition, long-wave radiation has not significantly changed in the corresponding
period.
The cloud radiative effect was determined using radiative transfer calculations for the cloud-free shortwave radiation and an empirical scheme for the cloud-free long-wave radiation. The uncertainty of the
-2
models is approximately 7 % and 7 Wm for the short- and long-wave, respectively. The annual net
-2
-2
cloud radiative effect is negative at all stations ranging from -4 Wm at Jungfraujoch to -38 Wm at
Payerne. Thus, clouds have currently a cooling effect on Earth´s climate. Results of the trend
-2
calculations indicate that the net cloud radiative effect has decreased by up to 7.5 Wm which implies
a reduction in fractional cloud cover or a shift towards a more transparent cloud type over the four
Swiss sites.
This study also demonstrates the difficulty in detecting trends with high confidence due to the
shortness of the time period for which the calculated changes are within the natural variability, the
instrumental and/or the model uncertainty.
Page | 344
TU-19_A4.2
Waves in the ocean under an ice cover
1
2
Sergey Muzylev , Elena Morozova
1
2
Shirshov Institute of Oceanology, Moscow, Russian Federation, Prokhorov General Physics Institute,
Moscow, Russian Federation
A compact ice cover under natural conditions can be treated as a thin elastic plate floating on the sea
surface. A theoretical description of the waves under the ice cover should take into account its elastic
properties as well as compression forces, and ice buoyancy. If the processes occuring inside the ice
cover are ignored and the sea water is assumed to be inviscid and incompressible, the main equations
for the waves under the ice cover should coincide with respective equations for the ice-free surface.
The only exception is the dynamic condition for the pressure at the water-ice boundary.
We obtained and analyzed explicit solutions for the flexural-gravity, internal, edge, Kelvin and Poincaré
waves, as well as the dispersion equations. All wave model problems are treated under a unified
approach and without the use of the hydrostatic (long-wave) approximation.
According to our results for internal waves under ice cover, the deflections of the sea ice surface at
frequencies close to but smaller than the Brunt-Väisälä frequency (i.e., with periods of tens of minutes)
can be large enough for the waves to be recorded instrumentally. This means that the use of the rigid
lid approximation for the vertical velocity in problems involving ice cover, can lead to erroneous
conclusions.
Edge waves in ice-covered water were analyzed using the theory for a plane-sloping beach with a
straight coastline. The existence of ice cover leads to a more complex behavior of ice deflections
along the normal to the coast, especially within the domain of high frequency edge waves.
It is shown, that the hydrostatic approximation artificially increases the order of the equations on
spatial variables in problems where the influence of ice cover is taken into account.
A comparison of the theory with observations in the Arctic Ocean showed a satisfactory agreement.
Page | 345
TU-20_A4.2
Low level jet streams at the sea ice edge - numerical experiments using WRF
1
Stefan Keiderling
1
Geophysical Institute, University of Bergen, Bergen, Norway
Marine activities at high latitudes are often encountering difficult conditions. Two severe factors are
strong winds and resulting rough seas. The goal is to make better forecasts so that operations in the
Arctic seas can receive more precise warnings and thus prepare better for potentially dangerous
situations. This can be achieved by more research on the special features of the lower Arctic
troposphere. Therefore this work will focus on low level jet streams at the sea ice edge. Since this
topic has not been much in the focus of previous studies there are rather few observations, hence the
first step is to reproduce the simulations made by Grønås and Skeie [1999]. For this purpose the
Weather Research and Forecasting Model (WRF) is used.
Analyses of the lower troposphere reveal strong boundary layer fronts connected with highly non
geostrophic winds. Wind maxima up to 36 m/s are found at heights of 925 hPa. The assumption is that
the low level jet and the boundary layer front are strongly connected, but not in a quasi-gesostrophic
nor semi-geostrophic sense, since neither quasi-geostrophy nor semi-geostrophy predicts those such
winds for this case. The aim is to explain the genesis of these jets along the ice edge.
Page | 346
TU-21_A4.2
Artificial neuronal network: determination of temperature and pressure
patterns to forecast sea ice fields in the Arctic and Antarctica
1
1
1
Federico Orquera , Mariano A. Torchio , Sandra C.B. Barreira
1
Meteorology, Argentine Naval Hydrographic Service, Ciudad Autónoma de Buenos Aires, Argentina
Monthly sea ice anomalies derived from passive microwave satellite data for the Arctic and Antarctica
spanning the period 1979-2011 are classified into 12 different patterns (6 for summer-autumn and 6
for winter-spring) for the Arctic Ocean and 16 different patterns (10 for summer-autumn and 6 for
winter-spring) for the Antarctic seas. Each of these patterns has an atmospheric temperature and
pressure structure associated with it (i.e., a specific mode of climate variability). These results were
obtained using principal component analysis (PCA) in T-Mode. Here we attempt to identify the sea ice
pattern for 2011-12 without using the passive microwave data, and instead using what can be inferred
from the temperature and pressure fields associated with the patterns. We approach this issue with a
multilayer Perceptron (neuronal network) with supervised learning and a back-propagation algorithm.
The Perceptron is the most common Artificial Neural Network topology dedicated to pattern
recognition. It was implemented through the use of temperature and pressure anomalies fields that
were associated with a group of sea ice anomaly patterns. The variables analyzed included only
composites of surface air temperature and pressure to simplify the density of input data and avoid a
non-converging solution (monthly input data for the period 1979-2010). The results of this analysis can
be used to identify the sea ice patterns without the need of a new PCA analysis of the sea ice data.
The objective of this study was an accurate classification of the past sea ice fields based on pressure
and temperature, to develop a tool to use those results to reconstruct previous to satellite period sea
ice fields and implement a forecast.
Page | 347
TU-22_A4.2
Validation of SAC-D/Aquarius MWR sea ice concentration
1
1
2
1
3
Claudia Carrrascal , Sandra Barreira , Sergio Masuelli , Héctor Salgado , Linwood Jones
1
2
Meteorology, Argentine Naval Hydrographic Service, Buenos Aires, Argentina, National Space
3
Agency of Argentina, Córdoba, Argentina, Electrical & Computer Engineering, Central Florida Remote
Sensing Laboratory, Orlando, United States
The National Space Agency of Argentina (CONAE) developed the SAC-D/Aquarius science mission
(launched in June 2011), together with the National Aeronautics and Space Administration (NASA).
One of the sensors on board the SAC-D is a MWR (Micro Wave Radiometer). This instrument is a
three channel push broom microwave radiometer with 8 antenna beams per channel and two different
incident angles (52° and 58°), that provides a measurement swath of approximately 380 Km. These
channels provide 36.5 GHz dual horizontal and vertical polarized and 23.8 GHz horizontal polarized
radiance measurements in an overlapping swath with the L-band Aquarius radiometer/scatterometer.
Geophysical variables over marine surface, such as, columnar water vapor, wind speed, sea ice
concentration, and rain rate are generated with the data comming from MWR
Sea ice is a significant characteristic of the polar ocean environment and influences the Earth's global
climate. Bootstrap and the NASA Team algorithms have been designed to estimate sea ice
concentration and type using microwave emissions. These algorithms rely primarily on the factor that
polarization and spectrum are different for sea ice and open Ocean.
CONAE developed an algorithm with the collaboration of CFRSL (Central Florida Remote Sensing
Laboratory) and SHN (Argentine Naval Hydrographic Service), for the sea ice concentration using data
coming from MWR radiometer. This algorithm is based on differences between brightness
temperatures corresponding to vertical and horizontal polarization of 36.5 GHz band and the gradient
corresponding to values of 36.5 and 23.8 GHZ in horizontal polarization. A validation process was
implemented with the collaboration of SHN researchers, using the sea ice concentration obtained from
National Snow and Ice Data Center (NSIDC) for comparisons.
We present the results of Sea Ice Concentration obtained using the CONAE algorithm for both, north
and south poles and a validation analysis of those estimations.
Page | 348
TU-23_A4.2
Clustering and categorization of sea ice fields in Arctic AND Antarctica using a
neural network
1
1
1
Mariano Torchio , Federico Orquera , Sandra Barreira
1
Meteorological Department, Argentine Navy Hydrographic Service, Buenos Aires, Argentina
Monthly sea ice anomalies derived from passive microwave satellite data spanning the period 19792012 were classified into 12 different patterns (6 for summer and autumn and 6 for winter and spring)
for the Arctic and 16 different patterns (6 for summer and autumn and 10 for winter and spring period)
for the Antarctica by means of Principal Component Analysis. Each of these patterns has an
atmospheric temperature and pressure structure associated with it (i.e., a specific mode of climate
variability). The goal of this project is to automate the classification process of the sea ice patterns and
the associated atmospheric patterns without using the later ones. Pattern recognition and later
categorization are accomplished by implementing an artificial neural network using a Self-organizing
Map topology. The network was trained using known sea ice concentration patterns previously
classified. When a new set of sea ice data is available (for example, 2013 data), it is presented to the
network. The network is able to cluster in pre-established categories or, if a pattern does not match in
any known category, a new one is automatically created. Expected results accurately classify any data
into existing patterns and, analyze if new categories created by the network are significant. This kind
of methodology is not only useful to obtain in which category a new set of sea ice data is but to obtain
the corresponding atmospheric pattern without performing PCA again to the entire set of data. The
findings are useful for sea ice modeling and prediction and also for accurate planning of future
missions to the Arctic and the Antarctica.
Page | 349
TU-24_A4.2
Sea-ice Environmental Research Facility (SERF)
1
1
1
1,2,3
Feiyue Wang , David Barber , Tim Papakyriakou , Soren Rysgaard
1
2
Centre for Earth Observation Science, University of Manitoba, Winnipeg, Canada, Greenland
3
Climate Research Centre, Greenland Institute of Natural Resources, Nuuk, Greenland, Arctic
Research Centre, Aarhus University, Aarhus, Denmark
The Sea-ice Environmental Research Facility (SERF) is the first experimental sea-ice facility in
Canada. Located in Winnipeg on the campus of the University of Manitoba, the main feature of SERF
is an outdoor seawater pool (60 feet long, 30 feet wide and 8 feet deep) with a movable roof,
numerous in situ sensors and instruments, and an on site trailer laboratory. Sea ice can be created at
the pool under various controlled conditions (e.g., seawater chemistry, snow cover, heating) with the
additions of chemical, isotopic and/or microbiological tracers. During its first two years of operation
(2011-2013), several types of sea ice including pancake ice and frost flowers were successfully
created at the SERF pool. Real-time monitoring has been carried out on surface and optical properties
and on the evolution of temperature, salinity, dissolved oxygen, pH, alkalinity, pCO2, and mercury in
and across the sea ice environment. The results demonstrate that SERF could provide a unique
research platform for hypothesis-driven, mesocosm-scale studies to examine geophysical properties
and biogeochemical processes in the sea ice environment.
Page | 350
TU-25_A4.2
Sea-ice boundary conditions in a mesoscale atmospheric model of the Baltic
Sea region
1
Agnieszka Herman
1
Institute of Oceanography, University of Gdansk, Gdansk, Poland
The Baltic Sea is a small, seasonally ice-covered water basin with complicated coastline and bottom
topography. Its sea surface temperature (SST) and - in winter - sea ice concentration and thickness
vary strongly in time and space in response to changing atmospheric circulation. Both SST and seaice properties are a shaped by a combination of thermodynamic and dynamic processes at the
atmosphere-ice-water interface. The resulting high temporal and spatial variability of the SST and seaice is difficult to assess on a regular basis. Therefore, the existing mesoscale atmospheric models of
the Baltic Sea region rely on low resolution data as a source of the lower-boundary conditions (LBC).
Consequently, they are not able to reproduce the properties of the atmospheric boundary layer (ABL)
in areas and situations when local conditions deviate from a larger-scale average (e.g., upwelling
regions, areas covered with fragmented ice at medium concentration, etc.). Moreover, the (rather
crude) treatment of sea ice typically used in weather models is unsuitable for thin, fragmented
seasonal ice.
In this study, the Weather Research and Forecasting (WRF) model is used to assess the influence of
the SST and sea ice data on the simulated ABL properties over the Baltic Sea in winter. To this end,
the simulations are performed with a 'standard' low-resolution LBC and with high-resolution LBC, and
the results are compared with available surface and upper-air observational data. In particular, the
analysis concentrates on the atmosphere-ocean heat and moisture fluxes, and on their sensitivity to
the (spatially and temporarily variable) sea ice thickness and concentration. Depending on the wind
conditions, the improved sea-ice treatment leads to significant improvements in the model
performance not only at coastal locations, but further inland as well, underlying the importance of seaice-atmosphere interactions in shaping the weather of the Baltic Sea region.
Page | 351
TU-26_A4.2
The effect of cloud and surface albedo on Arctic sea ice concentration
1
2
1
3
Sun-Kyong Hur , Yong-Sang Choi , Chang-Hoi Ho , Baek-Min Kim
1
School of Earth and Environmental Sciences, Seoul National University, Seoul, Korea, Republic of,
2
3
Environmental science and engineering, Ewha womans university, Seoul, Korea, Republic of, Korea
Polar Research Institute, KOPRI, Incheon, Korea, Republic of
Sea ice concentration (SIC) over the Arctic has decreased over the past few decades while the
absorbed solar radiation at the surface(ASR) has increased with global warming. In this study,
relationship between SIC and ASR is examined for Arctic region (over 65N). Cross-correlation analysis
shows that ASR has influence to SIC up to 3 month time lag according to its region. SIC also has
influence to ASR with ice-albedo feedback. ASR is calculated from satellite data depending on the
surface albedo, cloud forcing, and solar incidence. Correlation between ASR and surface albedo,
cloud forcing, and solar incidence differs seasonally. Thus, the effect of cloud and surface albedo on
the change of Arctic sea ice concentration differs seasonally and regionally.
Page | 352
TU-27_A4.2
Skill of September Sea Ice Extent in the GloSea5 Seasonal Prediction System
1
1
1
Drew Peterson , Ann B. Keen , Helene T. Hewitt , Alberto Arribas
1
UK Met Office, Exeter, United Kingdom
1
Over the past three years, the UKMO has participated in the Study of Environmental Arctic Change
(SEARCH) sea ice outlook which attempts to coalesce and compare various outlooks for September
sea ice extent made from observations available at the start of May. This year will represent the first
opportunity to evaluate our contribution to the outlook in the GloSea5 high resolution (~50km
Atmosphere, ~25km Ocean) seasonal prediction system. Using the GloSea4 system with initialization
to observed ice concentrations over the past two outlooks we have demonstrated fairly high skill in our
ability to produce historical forecasts of September Sea Ice extent for the period 1996-2009, with
typical correlations with the observed ice extents of 0.6 when initializing the system around the end of
March and beginning of April. The forecast potential of the system has also been encouraging, with
the observed sea ice extent in both 2011 and 2012 falling within the range of possibilities predicted
through the ensemble prediction system.
We will present the most recent analysis and forecasts from our high-resolution system.
Page | 353
TU-28_A4.2
Asymmetry variability between the Arctic and Antarctic sea ice
1
1
1
Fei Huang , Xiao Zhou , Ting-Ting Fan , Rong-Wang Zhang
1
Ocean University of China, Qingdao, China
1
It is known that the Arctic sea ice extent (SIE) reduced dramatically during the past 30 years, while the
Antarctic sea ice extent appeared a slightly rising trend under the global warming background. Besides
the linear trend difference of total SIE in Arctic and Antarctic, dominant modes on seasonal and
interannual and decadal timescales also shows different features between Arctic and Antarctic. On the
seasonal timescale, asymmetry variability between the Arctic and Antarctic sea ice mainly appears in
semi-annual variation. On the interannual and decadal timescales, the Arctic total SIE is dominant by a
descending trend, while the Antarctic total SIE appears significant interannual and decadal
variabilities. In order to investigated the detailed spatial and temporal asymmetry variability between
the Arctic and Antarctic sea ice and their season-dependent evolving process, a season-reliant
empirical orthogonal function (S-EOF) analysis onto the sea ice concentration (SIC) from 1979 to 2007
was performed. It is found that the first leading mode, accounts for 12.1% of total variance, shows a
descending trend in principal component (PC) in the past 30 years, especially in the latest decade,
mostly reflecting the declining of the Arctic sea ice trend. The Arctic appears consistent sea ice melting
while in most regions around the Antarctic continent except for the Bellingshausen Sea and
Amundsen Sea around western Antarctic, the SIC shows an increasing trend. The second significant
mode, which account for 10.1% of total variance, mostly indicates the interannual and decadal
oscillation of the Antarctic sea ice with a seesaw pattern between the northwest part and other sectors
around the Antarctic. This mode may relevant to an out-of-phase oscillation of joint annular mode
between two hemispheres in the atmosphere, which links the two hemispheres by a wave-train-like
“atmosphere bridge” through the central Pacific across Equator in transition seasons.
Page | 354
TU-29_A4.2
Progress and assessment of the Arctic & sub-polar North Atlantic state
estimate
1
1
2
3
An Nguyen , Patrick Heimbach , Rui Ponte , Ian Fenty
1
Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge,
2
3
United States, Atmospheric and Environmental Research, Inc., Lexington, United States, Oceans
and Ice, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, United States
The Arctic Ocean and sub-polar North Atlantic are home to processes of great importance to the
global climate system. These processes include the modulation of heat, moisture, and momentum
fluxes between the atmosphere and ocean by sea ice, the ice albedo feedback which regulates the
radiative budget, deep water formation in the Greenland and Labrador Seas which affect deep ocean
circulation and energy transport, and a coupling between ocean heat and marine terminating glacier
melt rates around the marginal Greenland ice sheet. To advance our understanding in this region, we
produce an eddy-permitting Arctic and sub-polar North Atlantic state estimate (ASTE) for climate
studies using the state estimation techniques developed within the framework of the ECCO
consortium. Data constraints for the state estimate will include hydrographic profiles from Argo floats,
ice-tethered profilers, a modern climatology, and moored arrays; sea ice observations such as
concentration, thickness, and velocity; and the near-surface atmospheric state from several
reanalyses. The estimation period is from 1992 to present. The ASTE domain includes the entire
Arctic Ocean and the Atlantic Ocean north of -30 degrees and has a horizontal resolution of 13-30 km
with 50 vertical levels. The dynamical consistency of the state estimate will permit closed budget
calculations of time-varying tracers such as heat and freshwater. The solution is expected to serve as
baseline for future observation sensitivity experiments and as a starting point for observationallyconstrained very high resolution nested regional simulations.
Page | 355
TU-30_A4.2
Impact of retreating sea ice on cloud over the Arctic Ocean in coupled GCM,
MIROC
1,2
2
2
1,2,3
Manabu Abe , Toru Nozawa , Tomoo Ogura , Kumiko Takata
1
2
National Institute of Polar Research, Tokyo, Japan, National Institute for Environmental Studies,
3
Tsukuba, Japan, JAMSTEC, Yokohama, Japan
The Ice-Albedo Feedback is thought to have a main role in the Arctic Amplification (AA). Arctic sea ice
has been reducing in recent decades. Coupled atmosphere-ocean general circulation models (GCMs)
also have simulated retreat of the sea ice in 20th century simulations, although the reduction rate is
not consistent with the observations. On the other hand, the AA may be affected by a feedback of
downward longwave radiation at surface enhanced by an increasing cloud over the Arctic region.
Observed cloud cover in the Arctic region during cold season (autumn-winter) increased due to the
reduction of sea ice (e.g., Liu, et al. 2012). Therefore, understanding a relationship between the
reduced sea ice and cloud cover change leads to partly unraveling a mechanism of the AA in the
future. In this study, we investigate an impact of the reduced sea ice on the cloud cover over the Arctic
Ocean during recent global warming period simulated by the coupled GCM, MIROC5.
In a simulation during 1976-2005, as the Arctic sea ice decreases with global warming, decreasing
trends of sea ice area over the Arctic Ocean are found in all months. The maximum reduction of sea
ice area occurs in September. On the other hand, the low-level cloud cover averaged over the Arctic
Ocean increases during autumn-winter. The maximum occurs in October. In August, although retreat
in sea ice is similar to that in September, significant increasing trend in cloud cover is not found. From
September, increasing trend of low-level cloud appears over girds with reduced sea ice. In September
and October, when the sea ice reduced, evaporation and heating from the ocean surface to air
temperature just above surface are enhanced. Thus, stability of low-level atmosphere is weakened,
resulting in increase in low-level cloud.
Page | 356
TU-31_A4.2
Long-term trend and variability in the Arctic sea ice turning angle and their
implications
1
1
1,2
1
Jinro Ukita , Meiji Honda , Katsushi Iwamoto , Shouta Ishizuka
1
2
Niigata University, Niigata, Japan, National Institute of Polar Research, Tachikawa, Japan
The motion of sea ice is under influences of forcing from winds and currents and of sea ice properties.
In facing rapidly changing Arctic climate we are interested in whether we observe and quantify
changes in sea ice conditions reflected in its velocity field. Theoretical consideration on the freedrift
model predicts a change in the sea ice turning angle with respect to the direction of forcing wind in
association with thinning sea ice thickness. Changes in atmospheric and ocean boundary layer
conditions may be reflected in the sea ice turning angle through modification of both atmospheric and
oceanic Ekman spirals. With these in mind this study examines statistical properties of the turning
angle of the Arctic sea ice and compares them with atmospheric/ice/ocean conditions for the period of
1979-2010 on the basis of IABP buoy data. Preliminary results indicate that over this period the turning
angle has varying trends depending on different seasons. We found significant (>90% level) changes
in the turning angle averaged for August to October with the maximum trend occurred in October. The
direction of trends is counter-clockwise with respect to the geostrophic wind direction, thus being
consistent with the thinning of sea ice predicted by the theory. However, in recent years the turning
angle appears to co-vary with the surface air temperature, further providing supporting evidence for
the relationship between the angle and sea ice thickness. In the presentation we will provide results on
the relationships between the turning angle and atmospheric and oceanic variables and further
discuss their implications.
Page | 357
TU-32_A4.2
Sea wave activity in the Arctic Ocean and its changes in the 21st century from
model simulations
1
1
1
2
2
Vyacheslav C. Khon , Igor I. Mokhov , Fedor Pogarskiy , Annette Rinke , Klaus Dethloff
1
2
A. M. Obukhov Institute of Atmospheric Physics RAS, Moscow, Russian Federation, Alfred Wegener
Institute for Polar and Marine Research, Potsdam, Germany
Rapid decline of sea ice cover during the last decades is important factor effecting the development of
Arctic marine transport systems and shelf deposit exploration. At the same time, this region is
influenced by extreme weather events, such as heavy storms with strong sea waves enhancing a
hazard for shipping, fishing and for shelf objects. Therefore, the model assessments of extreme storm
events and associated sea wave activity have imperative importance for estimations of possible
consequences for the shelf exploration and marine navigation.
In the present study spectral numerical model of sea waves (WAVEWATCH III) has been applied to
analyze sea wave activity in the Arctic basin in the 21st century using the regional climate model
HIRHAM forced by anthropogenic scenario SRES-A1B. The wave heights in the Arctic basin for the
1980-1999 are compared to that simulated for the middle (2045-2064) and the end (2080-2099) of the
21st century.
Our model results show an enhanced fraction of waves with significant height more than 2 m in
different areas of the Arctic basin, which is basically related with increasing the length of the wave runup in the middle of the 21st century. The frequency of days with strong winds and vigorous waves
increases for the Russian Arctic seas, with the largest growth simulated for the Kara Sea region during
October-December. In general, the Arctic sea ice reduction should facilitate strengthening the sea
wave activity. In particular, by middle of the 21st century, the model simulates the strongest increase
of extreme waves frequency for the Kara and Chukchi Seas during October-December. However, for
the areas with the predominant ice-free conditions for the present-day climate (the Barents Sea) the
model simulates a weakening of wave activity in the 21st century mainly due to reduction in the
surface wind speed.
Page | 358
TU-33_A4.2
Laptev Sea and East Siberian Sea fast ice variability
1
1
Valeria Selyuzhenok , Thomas Krumpen , Ruediger Gerdes
1
AWI, Bremerhaven, Germany
1
Laptev and East Siberian Seas are characterised by the greatest fast ice extent in the Arctic. However
there is a lack of studies concerning fast ice formation and break up as well as trends in fast ice area
and extent in these regions. This study aims to close this gap by investigating spatial and temporal
variability of Laptev Sea and East Siberian Sea fast ice extent. Information on fast ice extent was
obtained from sea ice charts and remote sensing data from1980 to 2012. The poster presents
seasonal cycle of fast ice growth and decay as well as interanual variability in its area and extent.
Furthermore, we provide insight into the mechanisms controlling formation and break up of fast ice by
linking fast ice occurrence to atmospheric processes as well as bathymetric features.
Page | 359
TU-34_A4.2
Air-sea interactions during an Arctic storm
1
1
Will Perrie , Zhenxia Long
1
Bedford Institute of Oceanography, Dartmouth, Canada
The impacts of increased open water in the Beaufort Sea were investigated for a summer Arctic storm
in 2008 using a coupled atmosphere-ice-ocean model. The storm originated in northern Siberia and
slowly moved into the Beaufort Sea along the ice edge in late July. The maximum wind when the
storm was over open water near the Beaufort Sea coast, after it had moved over the Chukchi and
Beaufort Seas. The coupled model system is shown to simulate the storm track, intensity, maximum
wind speed and the ice cover well. The model simulations suggest that the lack of ice cover in the
Beaufort Sea during the storm results in increased local surface wind and surface air temperature,
compared to enhanced ice cover such as occurred in past decades. In addition, due to this increase of
open water, the surface latent and sensible heat fluxes into the atmosphere are significantly
increased. However, there were no significant impacts on the storm track. The expanded open water
o
and the loss of the sea ice results in increases in the surface air temperature by as much as 8 C.
Although the atmospheric warming mostly occurs in the boundary layer, there is increased
atmospheric boundary turbulence and downward kinetic energy transport that reach to mid-levels of
the troposphere and beyond. These changes result in enhanced surface winds, by up to 4 m/s during
the 2008 storm, compared to higher ice concentration conditions (typical of past decades). The
dominant sea surface temperature response to the storm occurs over open water; with stormo
generated mixing in the upper ocean results in sea surface cooling of up to 2 C along the southern
Beaufort Sea coastal waters. The Ekman divergence associated with the storm caused a decrease in
the fresh water content in the central Beaufort Sea by about 11 cm.
Page | 360
TU-35_A4.2
Autonomous observation of solar radiation, sea ice and interaction with upper
ocean in the high-Arctic
1
1
2
1
1
Caixin Wang , Sebastian Gerland , Marcel Nicolaus , Mats A. Granskog , Stephen R. Hudson ,
3
4
4
4
Donald K. Perovich , Fernanda Jardon , Jean-Claude Gascard , Christine Provost , Nathalie
4
1
1
Sennechael , Tor I. Karlsen , Kristen Fossan
1
2
Norwegian Polar Institute, tromso, Norway, Alfred Wegener Institute for Polar and Marine Research,
3
Bremerhaven, Germany, Cold Regions Research and Engineering Laboratory, Hanover, United
4
States, Université Pierre et Marie Curie, Paris, France
The decline and thinning of Arctic sea ice have altered the interaction of solar radiation and sea ice.
To improve our understanding of this interaction, a Spectral Radiation Buoy (SRB) for measuring sea
ice optical properties was developed, based on a system used during the last International Polar Year
at the drift of the “Tara” across the Arctic Ocean. A first version of the SRB was deployed on drifting
ice in the high Arctic in April 2012. It includes three Satlantic spectral radiometers (two in air, one
under ice, with wavelength from 347-804 nm), a bio-shutter to protect the under-ice radiometer, a data
logger to handle and store collected data, and an Iridium satellite modem to transfer data. The underice radiometer is mounted on an adjustable under-ice arm, and the other instruments are mounted on
a triangular frame on top of the sea ice surface. The SRB measures simultaneously, autonomously
and continuously the spectral fluxes of incident and reflected solar radiation, as well as under-ice
irradiance. The system drifted about 1100 km, from a position near the North Pole (89°32´ N) to the
Fram Strait (79°40´ N). The collected data demonstrate that this system is suitable for autonomous
and long-term observations over and under sea ice in harsh conditions. Along with the SRB,
commercially available Ice Mass Balance buoys (IMB, MetOcean and SAMS) and LOCEAN icetethered CTD profiler were deployed on the same ice floe. Surface albedo decreased and the
transmittance through the snow and ice increased after mid-April coincident with snow melt. Decrease
of albedo and increase of transmittance in July is consistent with warming of upper ocean water.
Page | 361
TU-36_A6.3
Greenland ice sheet: surface mass balance change and its impact on future
sea level rise
1
1
1
Mikhail Geyer , David Salas y Mélia , Eric Brun
1
Centre National de Recherches Météorologiques/Météo-France, Toulouse, France
In this study we aim to estimate the future contribution of changes in surface mass balance (SMB) of
the Greenland ice sheet (GrIS) to sea level rise until 2100. We do not consider dynamics and basal
melt here. To this end, climate simulations performed with GCM CNRM-CM5.1(CMIP5) were used for
1850-2300, where from year 2006 two scenarios RCP4.5 and RCP8.5 were considered. The SMB was
evaluated in two different ways: directly as simulated by CNRM-CM5.1 and by using the detailed
snow-pack model CROCUS driven by CNRM-CM5.1 surface atmospheric forcings. A statistical
technique was developed to downscale the SMB from the 150km CNRM-CM5.1 grid to a 15km
resolution based on ETOPO1 and to take into account the feedback between the ongoing changes in
GrIS topography and SMB. This technique will be later used for the coupling of GRISLI ice sheet
model to CNRM-CM5.1, where the downscaling is essential. For the present climate, the estimated
sea level rise rate induced only by GrIS SMB change is +0.25mm/y, which is about 30% of the
contemporary total GrIS contribution (SMB+ice dynamics+basal melt) observed by satellites. The
simulations show that for 2100 this rate doubles (RCP4.5) and quadruples (RCP8.5). This results in a
sea level rise of +3cm (RCP4.5) and +4.5cm (RCP8.5) respectively by the end of the century. Our
results show that the projected annual ablation area covers 17%(RCP4.5) and 23%(RCP8.5) of the
GrIS surface in 2100, compared to 13% under present climate. For RCP8.5 scenario the melting rate
of GrIS is expected to accelerate very rapidly after the second half of the 21st century. It reveals a
strong amplification of the mass loss between 67°N and 70°N, which may lead to a future partition of
the GrIS in one small southern and one bigger northern ice sheet, under sustained warming beyond
2100.
Page | 362
TU-37_A6.3
Surface melting and melt features on the Amery Ice Shelf - implications for ice
shelf, ice sheet stability
1,2
2
1,2
Stefan W. Vogel , Alex D. Fraser , Petra Heil
1
2
Australian Antarctic Division, Kingston, Australia, Antarctic Climate and Ecosystem CRC, Hobart,
Australia
A general notion about Antarctica is that it is dry and cold. Yet along its coast line significant melting is
observed each summer. In various places melt water has been responsible for changes in the
dynamic of glaciers, ice sheet and ice shelves. One spectacular event was the collapse of the Larsen
B Ice Shelf. Here melt water ponding had a destabilising effect on the ice shelf. Melt water draining
through an ice sheet can enhance lubrication of the glacier bed leading to flow acceleration and
enhanced ice discharge. Freshwater input to the sub ice shelf environment may enhance thermohaline
circulation with the potential of enhancing the draw of warmer water masses into the sub ice shelf
cavity.
Here we present initial results investigating surface melting and surface melt-distribution on the
Lambert Graben- Amery Ice Shelf. Clearly visible from space, each year a network of lakes and rivers
forms on the surface of the Amery Ice Shelf south of Jetty Peninsula (~ 70.5 °S). Surface melt features
are absent in the front half of the Amery Ice Shelf likely due to high snow accumulation. Microwave
imagery as well as snow temperature data indicate melting with melt water percolation into and
refreezing inside the snow cover. Closer examination of satellite imagery shows an extensive surface
hydrological network covering the back of the Amery Ice Shelf transporting melt water over large
distances. During high melt years supra glacial lakes can reach tens of kilometres in length and >1
kilometre in width. The most southern surface lake is found adjacent to the Cumpston Massif on the
Mellor Glacier (73.5 °S). This is a significant distance upstream from the ice shelf grounding zone and
st
raises the possibility that surface melting under 21 climate warming scenarios could enhance
lubrication of East Antarctic outlet glaciers.
Page | 363
TU-38_B1.1
Heteroscedastic ensemble post-processing and hidden error variance theory
1
2
Craig Bishop , Elizabeth Satterfield
1
2
Marine Meteorology Division, Naval Research Laboratory, Monterey, United States, Naval Research
Laboratory, Monterey, United States
Ensemble variances provide a prediction of the flow dependent error variance of the ensemble mean
or, possibly, a high resolution forecast. However, small ensemble size, unaccounted for model error,
and imperfections in ensemble generation schemes cause the predictions of error variance to be
imperfect. Bishop et al. (2013 a,b) defined an analytic approximation to the posterior distribution of
error variances, given an imperfect ensemble prediction, based on parameters recovered from long
archives of innovation and ensemble variance pairs. This paper introduces heteroscedastic ensemble
postprocessing in which information from the estimated posterior distribution of error variances is used
to post-process ensemble forecasts. We design a hierarchy of post-processing methods, gradually
increasing the amount of information the ensemble has about the posterior distribution of error
variances. These “Straw man” ensembles are used to assess the value of knowledge of the mean and
variance of the posterior distribution to ensemble post-processing and explore its sensitivity to various
parameter regimes. We first apply our algorithm to synthetic ensembles and then to ensemble data
generated by an ensemble forecasting system for a non-linear Lorenz model. It was found that the
value of heteroscedastic post-processing increases as the correlation between raw ensemble variance
and error variance decreases. It is found that the value of knowledge of the relative variance of error
variances given an ensemble variance increases as the relative variance of the climatological
distribution of error variances increases. Preliminary results from post-processed operational
ensemble forecasts will also be presented.
Page | 364
TU-39_B1.1
A metric of non-Gaussianity of observation for the ensemble Kalman filters
1
Shin'ya Nakano
1
The Institute of Statistical Mathematics, Tachikawa, Japan
The ensemble Kalman filter (EnKF) and its variants are now widely applied to various data assimilation
problems because of its computational efficiency and portability. However, the EnKF assumes a linear
Gaussian observation model. Even if the observation is nonlinear or non-Gaussian, the EnKF requires
a linear Gaussian approximation of the observation model. An estimate obtained by the EnKF is thus
an approximation of the true posterior distribution. If the approximation of the observation model is
poor, the EnKF would not provide good estimates.
The present work proposes a metric for assessing the goodness of such a approximation. In order to
evaluate the discrepancy between the estimate by the EnKF and the true posterior distribution, we use
the importance sampling approach. Using the importance sampling technique, the discrepancy can be
evaluated by the entropy of the importance weights which represents the imbalance of the importance
weights. Since the discrepancy between the estimate by the EnKF and the true posterior distribution is
associated with a poorness of the linear Gaussian approximation of the observation model, the
entropy can be used as a metric of the goodness of this linear Gaussian approximation. Using this
metric, we could choose between a linear Gaussian algorithm such as the EnKF and a non-Gaussian
algorithm such as the particle filter for each analysis step.
Page | 365
TU-40_B1.1
Comparing of a stochastic and multiphysics approach in the ensemble
prediction system of Météo-France
1
Marie Boisserie
1
CNRM-GAME (Météo-France), Toulouse, France
A stochastic physics scheme to represent model error in the operational ensemble prediction system
of Météo-France is presented in this study. Over the past 20 years, more efforts have been given to
the representation of errors arising from the initial condition production. The representation of the
model error contribution is a more challenging task since the sources of this error are diverse and
partially known. In this study, we have attempted to estimate model error variances by subtracting the
predictability error variances from forecast error variances of spectral vorticity tendency. Then, this
spectral model error variances provide information for generating stochastic forcing functions. The
impact of the stochastic physics scheme is compared with that of the multiphysics approach currently
used at Météo-France to represent model error in the operational ensemble prediction system.
Some preliminary results first show that the implementation of the stochastic physics scheme
improves significantly the reliability of a 35-member ensemble (using only one physical
parametrization). Then, the comparison with the multiphysics approach indicates that the stochastic
physics scheme produces over Europe an ensemble as reliable as that using the multiphysics.
However, no significant impact are found in terms of resolution.
Page | 366
TU-41_B1.1
Benefits of extended range GEFS for the subseasonal forecast problem
1
1
1
1
Malaquias Pena , Dingchen Hou , Yuejian Zhu , Richard Wobus , Xiaqiong Zhou
1
EMC/NCEP, College Park, United States
1
The prediction skill of current global ensemble prediction systems permits obtaining useful information
even beyond two weeks for some atmospheric variables. An experimental version of the Global
Ensemble Forecast System (GEFS) at NCEP has been prepared to produce probabilistic forecasts out
to 5 weeks. The system is intended to provide a link between weather and seasonal (coupled oceanatmosphere) prediction systems and to become a benchmark to assess the impact of coupling of the
atmosphere model with the ocean model. Results from the experiments carried out show a significant
positive skill improvement with respect to the operational seasonal prediction system for the first two
weeks of lead time. This improvement is attributed primarily to a more sophisticated ensemble
initialization scheme than the seasonal prediction system, which uses a lagged approach. Another
benefit being explored is the anticipation of high amplitude persistent anomalies such as extratropical
blocks. The necessity to produce retrospective forecasts for the extended GEFS to remove systematic
errors is evident from the experiments particularly beyond one week.
Page | 367
TU-42_B1.1
A new structure for error covariancematrices in EnKF assimilation and their
adaptive estimation method
1
1
2
Xiaogu Zheng , Guocan Wu , Liqun Wang
1
College of Global Change and Earth System Science, Beijing Normal University, Beijing, China,
2
Department of Statistics, University of Manitoba, Winnipeg, Canada
Correctly estimating forecast error covariance matrix is a key step in any data assimilation scheme. If it
is not correctly estimated, the assimilated states could be far from the true states. A popular method to
address this problem is error covariance matrix inflation. That is, to multiply the forecast error
covariance matrix by an appropriate factor. In this paper, analysis states are used to construct forecast
error covariance matrix and an adaptive estimation procedure associated with the error covariance
matrix inflation technique is developed. The proposed assimilation scheme was tested on Lorenz-96
model, associated with spatially correlated observational systems. The experiments show that by
introducing the proposed structure of forecast error covariance matrix and applying its adaptive
estimation procedure, the assimilation results are further improved.
Page | 368
TU-43_B3.1
Three-dimensional structure and energetics of the Western Pacific
teleconnection pattern
1
1
1
1
Sho Tanaka , Hisashi Nakamura , Kazuaki Nishii , Takafumi Miyasaka
1
Research Center of Advanced Science and Technology, The University of Tokyo, Tokyo, Japan
The Western Pacific (WP) pattern is one of the teleconnection patterns defined originally by Wallace
and Gutzler (1981) in the wintertime Northern Hemisphere. It is characterized by north-south dipolar
anomalies in pressure over the Far East and western North Pacific, with meridional shift of a strong
upper-tropospheric westerly jet. By strengthening of the Siberian High, prominent positive events of
the WP pattern tend to give rise to cold-air outbreaks to eastern China, Korea and Japan. However,
the three-dimensional structure and energetics of the WP pattern are yet to be clarified, which are
investigated in this study through composite analysis. The compositing is based on 32 strong positive
monthly events in winter for which the WP pattern index exceeded a unit standard deviation for the
period of 1948-2010. The composited anomalies were then used for the energetics of the WP pattern.
Unlike most of the teleconnection patterns observed over the oceans that exhibit equivalent barotropic
structure, the composited monthly anomalies of the WP pattern exhibit baroclinic structure with their
phase lines tilting southward or southwestward with height. Owing to this baroclinic structure,
baroclinic energy conversion is found most efficient for maintaining the WP pattern against dissipative
processes including its heat exchange with the underlying ocean. The baroclinic conversion is
contributed to by westward and northwestward heat fluxes associated with the northern and southern
centers of action, respectively, of the pattern acting on the cold planetary-wave trough. Though
contributing positively to the maintenance, barotropic energy conversion is found less efficient as the
node of the dipolar pressure anomalies is displaced north of the climatological westerly jetstream in its
exit. Transient eddies act to maintain the monthly WP anomalies through their momentum transport
but damp them through their down-gradient heat transport.
Page | 369
TU-44_B3.1
Space-time spectral analysis of the Southern Hemisphere daily 500 hPa
geopotential height
1,2
1
Cheng Sun , Jianping Li
1
Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS), Beijing, China,
2
Department of Meteorology at University of Hawaii at Manoa, Honolulu, United States
In this paper the authors use NCEP2 reanalysis data from 1979 to 2004 to expand the daily 500 hPa
geopotential height in the Southern Hemisphere (SH, 90°-20°S) into a double Fourier series, and
analyze the temporal frequency characteristics of the expansion coefficients over various spatial
scales. For the daily series over the whole year, the coefficient series of the extratropical mean height
is characterized by a significant low-frequency (10-30 day) variation. For zonal waves with (k, l) = (1-5,
1), where k and l are the zonal and meridional wavenumbers, respectively, the low-frequency
variability is most pronounced for zonal wavenumbers 3 and 4, while the short wave with zonal
wavenumber 5 has significant high-frequency (4-8 day) variability. For meridional waves with (k, l) =
(0, 2-6), the meridional dipole (l = 2) makes a major contribution to the low-frequency variability,
consistent with the intraseasonal space-time features of the SH annular mode (SAM). The meridional
tripole (l = 3) also exhibits low-frequency variability. For two-dimensional waves (k, l) = (1-5, 2-6), the
dipole is a preferred meridional structure for intraseasonal modes with large zonal scales, indicating an
out-of-phase relationship between low-frequency planetary-scale waves at mid- and high-latitudes.
The diagnostic results outlined above can be explained, to a certain extent, by the dispersion relation
for Rossby waves. Theoretical analysis indicates that zonal wavenumber 3, zonally symmetric flow
such as SAM, and planetary-scale waves with meridional dipole structures may be interpreted as lowfrequency eigenmodes of the atmosphere.
Page | 370
TU-45_B3.1
Sensitivity of simulated climate to two atmospheric models: interpretation of
differences between dry models and moist models
1
2
1
He Zhang , Minghua Zhang , Qingcun Zeng
1
2
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China, School of Marine
and Atmospheric Sciences, Stony Brook University, New York, Armenia
The dynamical core of the Institute of Atmospheric Physics of the Chinese Academy of Sciences
Atmospheric General Circulation Model (IAP AGCM) and the Eulerian spectral transform dynamical
core of the Community Atmosphere Model (CAM3.1) developed at the National Center for
Atmospheric Research (NCAR) are used to study the sensitivity of simulated climate. We report that
when the dynamical cores are used with the same CAM3.1 physical parameterizations and with
comparable resolutions, the model with the IAP dynamical core simulated a colder troposphere than
that from the CAM3.1 core, reducing the CAM3.1 warm bias in the troposphere in the tropics and
middle latitudes. However, when the two dynamical cores are used in the idealized Held-Suarez tests
without moisture physics, the IAP AGCM core simulated a warmer troposphere than that in CAM3.1.
The causes of the differences in the full models and in the dry models are then investigated.
We show that the IAP dynamical core simulated weaker eddies in both the full physics and the dry
models than those in the CAM due to different numerical approximations. In the dry IAP model, the
weaker eddies cause smaller heat loss from poleward dynamical transport and thus warmer
troposphere in the tropics and middle latitudes. When moist physics is included, however, weaker
eddies also lead to weaker transport of water vapor and reduction of high clouds in the IAP model,
which then causes a colder troposphere due to reduced greenhouse warming of these clouds. Our
results show how interactive physical processes can change the effect of a dynamical core on climate
simulations between two models.
Page | 371
TU-46_B3.1
The role of cyclones and fronts for Southern Ocean precipitation and its
variability
1
1
2
2
1
1
Lukas Papritz , Stephan Pfahl , Irina Rudeva , Ian Simmonds , Harald Sodemann , Heini Wernli
1
2
ETH Zürich, Institute for Atmospheric and Climate Science, Zürich, Switzerland, School of Earth
Sciences, University of Melbourne, Melbourne, Australia
Exploring the relationship between the occurence of extratropical cyclones, fronts and precipitation
can help to constrain trends in precipitation over the Southern Ocean, as future changes in the
cyclone frequencies can likely be identified more easily. Based on the ERA-Interim dataset and
objective analysis of cyclones and fronts therein, we present a novel method to attribute intense
th
precipitation (> 75 percentile) to these weather systems. Our method allows to quantify the amount of
intense precipitation falling in association with extratropical cyclones and along fronts outside of
cyclones separately.
As will be shown, in certain regions of the Southern Ocean a major portion of intense precipitation is
caused by fronts. In particular in the cyclone sparse mid-latitudes of the South Indian Ocean intense
cold fronts, related to cyclones moving more southwards along the coast of Antarctica, account for up
to 70% of precipitation. In contrast during austral winter along the northern branch of the split
stormtrack in the Pacific, both cyclones and fronts contribute equally about 40% each. In a highlatitude band bending uniformly around the coast of Antarctica, cyclones account for up to 80% of the
precipitation.
We relate inter-annual variability of seasonal precipitation to changes in stormtrack activity, i.e., in
cyclone and front frequencies. Large variability is found in the south Atlantic and the south Pacific,
where the stormtrack is strongly influenced by ENSO. In JJA 1998 the Pacific subpolar stormtrack was
exceptionally strong, causing intense frontal precipitation between 45°S and 60°S. A potential cause of
this stormtrack anomaly was an amplified Eady growth rate off the ice edge related to SST anomalies,
leading to the reintensification of cyclones from the Indian Ocean, combined with a strong polar front
jet, typical for La-Nina conditions.
Page | 372
TU-47_B3.1
A Lagrangian climatology of tropical and extratropical forcing of the Northern
Hemisphere subtropical jet
1
Olivia Martius
1
Oeschger Centre for Climate Change Research and Institute of Geography, University of Bern, Bern,
Switzerland
The subtropical jet, located at the polar edge of the tropical Hadley cell, links tropical and extatropical
dynamics. Upper-level outflow of tropical convection creates wave disturbances that propagate
downstream along the subtropical jet waveguide and influence the weather in the extratropics.
The subtropical jet itself is also affected by tropical and extratropical dynamical systems. Besides the
classical Hadley cell forcing, Rossby waves and Rossby wave breaking in the extratropics and the
subtropics can substantially affect the subtropical jet:
•
•
From an angular momentum point of view (breaking) Rossby waves are effective in
transporting air from the tropics towards the subtropics, thereby potentially accelerating the
subtropical jet. At the same time the zonal pressure gradients associated with the waves affect
the conservation of angular momentum
From a potential vorticity (PV) point of view the subtropical jet is co-located with a zone of
strong PV gradients that demarks the transition from tropical tropospheric low PV air to
extratropical stratospheric high PV air. Breaking waves in the extratropics can transport highPV air equatorward and thereby increase the subtropical PV gradient.
Here the focus is on the forcing mechanisms of the subtropical jet during a five-year “climatological”
period addressing both the PV and the angular momentum point of view. This includes i) processes
that increase the PV gradient in the vicinity of the jet and ii) the angular momentum budget of air that
ends up in the subtropical jet. To this end trajectories were calculated backwards out of the jet starting
every 6 hours and tracing the angular momentum along the pathways of the air parcels prior to their
arrival in the jet.
A statistical analysis of the relative importance of tropical and extatropcial forcing for different seasons
will be presented and the role of extratropical dynamics for angular momentum non-conservation
discussed.
Page | 373
TU-48_B3.1
Dynamical significance and forecast verification of warm conveyor belts
1
1
1
1
2
Erica Madonna , Heini Wernli , Hanna Joos , Maxi Böttcher , Olivia Romppainen-Martius
1
2
ETH Zürich, Institute for Atmospheric and Climate Science, Zürich, Switzerland, University of Bern,
Oeschger-Centre for Climate Change Research and Institute of Geography, Bern, Switzerland
Warm conveyor belt (WCBs) are moist ascending airstream in extratropical cyclones. Climatologically,
they are key for the meridional and vertical transport of water vapor and heat.
The rapid ascent of WCBs from the boundary layer to the upper troposphere in about 1-2 days leads
to cloud formation, (intense) precipitation and the release of latent heat. Through diabatic processes
their potential vorticity (PV) value is modified in a significant way. Typically WCBs reach the
tropopause level with low PV values (~0.5 pvu) and through this cross-isentropic transport of low-PV
air they can amplify the upper-level Rossby waves and contribute to the formation of PV streamers
downstream. These in turn can act as precursors of extreme weather events and/or trigger the genesis
of another cyclone. Considering the quality of numerical weather predictions, an underestimation of
the frequency and/or intensity of WCBs can lead to an underprediction of the intensity of upper-level
ridges and in turn develop into a poor-quality medium-range weather forecast. It is therefore important
to quantify the quality of WCBs in numerical weather forecasts and to investigate the effects of a
misrepresentation of WCBs on the downstream flow.
In this study, WCBs are determined in operational analyses and deterministic forecasts from the global
ECMWF model. WCBs are identified from comprehensive trajectory calculations that select air parcels
in the vicinity of cyclones with a minimum ascent of 600 hPa in 48 hours. Using a feature-based
verification technique, errors in the location and intensity of WCBs in the ECMWF forecasts are
quantified in the North Atlantic for three winters. First results indicate that several episodes with a poor
forecast performance in terms of the 300-hPa geopotential height anomaly correlation coefficient are
also characterized by significant errors in the representation of WCBs.
Page | 374
TU-49_B3.1
Warm conveyor belts in the ERA-Interim data set (1979-2010): moisture origin
and relevance for precipitation extremes
1
1
1
1
1
Stephan Pfahl , Erica Madonna , Maxi Boettcher , Hanna Joos , Heini Wernli
1
Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
The effect of moisture on the evolution of extratropical cyclones is particularly pronounced within warm
conveyor belts (WCBs), which are coherent airstreams characterized by intense ascent, latent heat
release, and precipitation formation. In this study, a recent climatology of WCBs based on the ERAInterim reanalysis data set is applied for investigating two aspects of the WCB moisture cycle: the
sources of moisture and the relevance of WCBs for precipitation extremes.
The most important WCB moisture source regions are the western North Atlantic and North Pacific in
boreal winter and the South Pacific and western South Atlantic in boreal summer. During DJF, South
America is the strongest continental moisture source. In general, WCBs have more local and more
oceanic moisture source regions in winter compared to summer, when long range transport and
continental moisture recycling are also important. In many regions, WCB moisture supply is related to
anomalously strong surface evaporation, enforced by relatively low relative humidity (RH) and high
surface winds over the ocean and low RH and high skin temperatures over the continents.
WCBs are highly relevant for the occurrence of precipitation extremes in many parts of the
extratropics. The percentage of precipitation extremes directly associated with a WCB is larger than
70-80%, e.g., over the western North Atlantic and south-eastern North America, eastern China, Korea
and Japan as well as large parts of southern South America. A correct representation of WCBs in
weather forecast and climate models is thus essential for a good prediction of precipitation extremes.
Page | 375
TU-50_B3.1
The linkage between warm conveyor belts and liquid and ice water path and its
implications for cloud radiative forcing
1
1
Hanna Joos , Heini Wernli , Erica Madonna
1
IAC ETH, Zurich, Switzerland
1
Warm conveyor belts (WCBs) are the main cloud and precipitation forming airflows in extratropical
cyclones. They start in the atmospheric boundary layer in the warm sector of the cyclone and ascend
until they reach the upper troposphere in approximately 48 h. During the ascent, liquid, mixed and ice
phase clouds and precipitation are formed and WCBs can be identified on satellite imagery as
elongated cloud bands. As WCBs are common flow features in the extratropics, they contribute
substantially to the development of the observed pattern of precipitation and high liquid/ice water path
in the storm track regions. The high amount of liquid and ice water path in turn can strongly modify the
radiation in these regions.
In this study a Lagrangian analysis is used in order to identify WCBs based on the erainterim dataset.
The evolution of precipitation, liquid/ice water path and cloud radiative forcing along the ascending
trajectories is investigated and compared to the climatological mean values. It can be seen that WCBs
are responsible for a large part of the precipitation pattern as well as the observed high liquid/ice water
path values in the extratropical storm tracks. Due to this strong link between WCBs and high liquid/ice
water path values, the long wave and short wave radiation and thus the cloud radiative forcing is also
strongly influenced by these airstreams. A correct representation of the dynamical features of WCBs
and the associated cloud forming mechanisms is therefore also crucial for climate models as they
strongly determine the precipitation pattern and are important for the radiative budget in the
extratropics.
Page | 376
TU-51_B3.1
Stationary Rossby waves and regional climatology
1
1,2
Robert Wills , Tapio Schneider
1
2
California Institute of Technology, Pasadena, United States, Department of Earth Sciences, ETH
Zurich, Zurich, Switzerland
Land surface processes such as biology, surface hydrology, erosion, and ice sheet dynamics are
controlled in part by the atmospheric forcing of precipitation, surface temperature, and the probabilistic
distribution of rare events such as floods, droughts, and heat waves. To better understand the
atmospheric forcing on these surface processes it is important to understand how large scale zonal
asymmetries such as mountain ranges, continental boundaries, and ice sheets affect the transport of
heat and moisture. We use an idealized GCM with a slab ocean to study the effect of a gaussian
mountain ridge on the regional climatology around the globe in a wide range of climates. We find that,
in addition to the well known effect of topographically driven stationary Rossby waves on zonal
anomalies in surface temperature, stationary waves cause large zonal anomalies in precipitation and
affect the spatial distribution of rare event statistics. The effect on rare event statistics arises from the
effect of stationary waves on the distribution of eddy kinetic energy and transient transport of heat and
moisture. With an increase in greenhouse gas concentrations, represented in our model by optical
thickness in a grey atmosphere, the amplitude of the stationary Rossby waves decreases while the
overall specific humidity of the atmosphere and associated moisture fluxes increase. This leads to a
maximum in the stationary wave induced precipitation pattern near the present value of optical
thickness. This is in contrast to the stationary wave induced surface temperature pattern that has the
largest amplitude in the coldest climates consistent with a dominance of the decrease in stationary
wave amplitude over the increasing temperature in a warming climate. A mechanistic understanding of
the influence of elevated topography on regional climatology in a changing climate is essential for
understanding the coupling of surface process dynamics with the atmosphere.
Page | 377
TU-52_B4.1
Comparisons of thermal effects of Tibetan Plateau with the NCEP-I and ERA-40
reanalysis data
1
1
1
Shanshan Zhong , Zhiwei Wu , Jinhai He
1
Key Laboratory of Meteorological Disaster of Ministry of Education，Nanjing University of Information
Science &Technology, Nanjing, China
Due to lack of sufficient observations over the Tibetan Plateau (TP), how to measure the strength of
thermal effects of TP is a challenging issue, yet of crucial importance for climate research. In this
study, two sets of daily reanalysis data(1961-2001) from the National Centers for Environmental
Prediction reanalysis version 1 (NCEP-I) and European Centre for Medium-Range Weather Forecasts
40-year reanalysis data (ERA-40) are used to calculate the atmospheric diabatic heating effects of TP
and its neighboring regions with an inverse-algorithm. The observational data obtained in the recent
experiments of atmospheric sciences over TP are applied to verify and evaluate those results from the
NCEP-I and ERA-40 reanalysis data, respectively. It is found that the ERA-40 result is closer to the
observations in terms of the structure and seasonal variation of the vertical profile of the atmospheric
diabatic heating over TP. The horizontal distributions of the apparent heat source are quite reasonable
over Asia for both the NCEP-I and ERA-40 results.
Page | 378
TU-53_B4.1
Trends in summer rainfall over China associated with the Tibetan Plateau
sensible heat source during 1980-2008
1
1
2
1
Meirong Wang , Anmin Duan , Yonghui Lei , Yangfan Cui
1
State Key Laboratory of Numerical Modelling for Atmospheric Sciences and Geophysical Fluid
2
Dynamics, Institute of Atmospheric Physics, Beijing, China, State Key Laboratory of Remote Sensing
Science, Institute of Remote Sensing Applications, Beijing, China
The impacts of the thermal forcing over the Tibetan Plateau (TP) in spring on changes in summer
rainfall in China are investigated using historical records from the period between 1980 and 2008. The
spring sensible heat (SH) flux and snow depth over the TP both decreased over this time period,
although the trend in SH was more significant than that in snow depth. The similarity between patterns
of precipitation trends over China and corresponding patterns of regression coefficients on the leading
mode of spring SH change over the TP demonstrates the distinct contribution of changes in TP SH
during spring. Enhanced precipitation in South China was accompanied by increases in heavy rainfall,
precipitation intensity, and the frequency of precipitation events, while reduced precipitation in North
China and Northeast China was primarily associated with decreases in the frequency of precipitation
events. Further analysis using observational data and numerical simulations reveals that the
reductions in SH over the TP have weakened the monsoon circulation and postponed the seasonal
reversal of the land-sea thermal contrast in East Asia. In addition, the positive spring SH anomaly may
generate a stronger summer atmospheric heat source over the TP due to the positive feedback
between diabatic heating and local circulation.
Page | 379
TU-54_B4.1
Preliminary multiproxy surface air temperature field reconstruction for China
over the past millennium
1
2
3
Feng Shi , Bao Yang , Lucien Von Gunten
1
State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid
2
Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China, Key
Laboratory of Desert and Desertification, Cold and Arid Regions Environmental and Engineering
3
Research Institute, Chinese Academy of Sciences, Lanzhou, China, Oeschger Centre for Climate
Change Research & Institute of Geography, University of Bern, Bern, Switzerland
We present the first millennial-length gridded field reconstruction of annual temperature for China, and
analyze the reconstruction for spatiotemporal changes and associated uncertainties, based on a
network of 415 well-distributed and accurately dated climatic proxy series. The new reconstruction
method is a modified form of the point-by-point regression (PPR) approach. The main difference is the
incorporation of the “composite plus scale” (CPS) and “Regularized errors-in-variables” (EIV)
algorithms to allow for the assimilation of various types of the proxy data. Furthermore, the search
radius is restricted to a grid size; this restriction helps effectively exclude proxy data possibly
correlated with temperature but belonging to a different climate region. The results indicate that: 1) the
past temperature record in China is spatially heterogenic, with variable correlations between cells in
time; 2) the late 20th century warming in China probably exceeds mean temperature levels at any
period of the past 1000 years, but the temperature anomalies of some grids in eastern China during
the Medieval climate anomaly period are warmer than during the modern warming; 3) the climatic
variability in the eastern and western regions of China was not synchronous during much of the last
millennium, probably due to the influence of the Tibetan Plateau. Our temperature reconstruction may
serve as a reference to test simulation results over the past millennium, and help to finely analyze the
spatial characteristics and the driving mechanism of the past temperature variability. However, the
lower reconstruction skill scores for some grid points underline that the present set of available proxy
data series is not yet sufficient to accurately reconstruct the heterogeneous climate of China in all
regions, and that there is the need for more highly resolved temperature proxies, particularly in the
Tibetan Plateau.
Page | 380
TU-55_B4.1
Establishment of the South-Asian High over the Indo-China Peninsula during
late spring to summer
1
2
1
Lijuan Wang , Aiguo Dai , Jinhai He
1
College of Atmospheric Sciences, Nanjing University of Information Science & Technology, Nanjing,
2
China, National Center for Atmospheric Research, Boulder, United States
The establishment of the upper-level South-Asian High (SAH) over the Indo-China Peninsula (ICP)
during late boreal spring and its possible causes are investigated using long-term NCEP/NCAR and
ERA-40 reanalysis and satellite-observed out-going longwave radiation (OLR) data. Results show that
during late April - early May the 150 hPa circulation exhibits a “two-cored” structure over Southeast
Asia, with a strong core moving rapidly towards to the ICP and a weak core over the waters southeast
o
of the Philippines. From early March to middle April, deep convection stays south of ~6 N over
o
o
northern Sumatra islands. As the maximum solar radiation moves over the latitudes (10 -20 N) of the
ICP in late April, the air over the ICP becomes unstable because of large surface sensible heating,
and it ascends over the ICP and descends over the adjacent waters to the east and west. This triggers
deep convection over the ICP that induces large latent heating and strong updrafts and upper-level
divergence, leading to the formation of an upper-level anti-cyclonic circulation and the SAH over the
ICP. During early-middle May, deep convection over the ICP intensifies and extends northwards and
-1
over to the adjacent waters. Strong latent heating (up to 3.5-4.0 K day ) from deep convection
enhances and maintains the strong updrafts and upper-level divergence, and the SAH is fully
established by middle May. Thus, the seasonal maximum solar heating and the land-sea contrast
around the ICP provide the basic conditions for deep convection to occur preferably over the ICP that
leads to the formation of the SAH over the ICP from late April to middle May. This movement of the
SAH from the western Pacific waters to the ICP following the maximum thermal heating during April
resembles SAH´s northwestward movement to the Tibetan Plateau from late May to early June.
Page | 381
TU-56_B4.1
Ocean forcing to the interdecadal change of summer rainfall in China around
the late-1990s
1
1
2
Yong Liu , Ronghui Huang , Gang Huang
1
Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of
2
Sciences, Beijing, China, Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences
(CAS), Beijing, China
Previous studies indicated an interdecadal change in the summer rainfall over China around the late1990s, and accompanying this interdecadal change, the summer rainfall increased over Southern
China and decreased over Northern China, featuring an anomalous “south-flood-north-drought”
pattern. The present work, using the observational and numerical studies, investigated the global
atmospheric circulation changes and the oceanic role that related to this intedecadal change. Results
showed that this interdecadal change had a global climate change background, corresponding to the
interdecadal change, the summer atmospheric circulation experienced notable changes with
symmetric features in the northern and southern hemisphere. And the global sea surface temperature
(SST) revealed remarkable changes as well, having SST warming over Indian Ocean and Atlantic
Ocean, and La Niña-like/PDO-like SST anomalies (SSTA) over Pacific Ocean. These features
suggested this interdecadal change may be a response to the tropical Ocean SST forcing, especially
the tropical Pacific Ocean SST changes. The numerical results using an AGCM forced by the tropical
SSTA, especially the tropical Pacific Ocean SSTA, resembled the observational results, confirming the
Ocean's role in the intedecadal change.
The possible mechanism whereby the tropical SSTA triggering the interdecadal change was explored
as well. There may be two ways: (1) Anomalous convection over tropical and subtropical areas
induced the tropical SSTA excited baroclinic Rossby waves which propagated polarward causing the
extratropical circulation changes; (2) Owing to the tropical SSTA forcing, the subtropical westerly jet in
the northern hemisphere weakened and shifted polarward. Changes in the subtropical jet influenced
the stationary and transient eddy momentum flux which affected the eddy-induced mean merdional
circulation, inducing ascending motion over subtropics and descending motion in the middle latitude.
Through above two ways the tropical Ocean SSTA may led to the interdecadal change around the
late-1990s.
Page | 382
TU-57_B4.1
Predictability of the western North Pacific summer climate associated with
different ENSO phases by ENSEMBLES multi-model seasonal forecasts
1
2
3
Chaofan Li , Riyu Lu , Buwen Dong
1
Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of
2
Sciences, Beijing, China, State Key Laboratory of Numerical Modelling for Atmospheric Sciences and
Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing,
3
China, National Centre for Atmospheric Science-Climate, Department of Meteorology, University of
Reading, Reading, United Kingdom
Predictability of the western North Pacific (WNP) summer climate associated with different ENSO
phases is investigated in this study based on the 1-month lead retrospective forecasts (hindcasts) of
five state-of-the-art coupled models from ENSEMBLES. During the hindcast period from 1960 to 2005,
the models well capture the WNP summer anomalies during most of years related to ENSO excepting
the La Niña decaying summers. In the El Niño decaying, El Niño developing and La Niña developing
summers, high prediction skills of the lower-tropospheric wind are found over the WNP for the WNP
summer monsoon index (WNPMI), with the prediction correlation larger than 0.7 and the prediction
bias lower than 0.6. Associated with the influences of ENSO, prediction skills of the sea surface
temperature (SST) are high over the trpoical Pacific Ocean and Indian Ocean, suggesting significant
contributions of ENSO to the predictabialiy of the WNP summer prediction. In addition, the prediction
poential demonstrated by the signal-to-noise ratio shows similar spatial destributions to those in the
prediction correlation and prediction bias. This further suggests that prediction skills of the WNP
summer climate mainly rely on the influence of ENSO and more attention should be paid onto the
predictibility of the WNP summer anomalies associated with different ENSO phases for their different
prediction skills.
Page | 383
TU-58_B4.1
Possible impacts of thermal anomalies in East China Sea on East Asian
atmospheric circulation and precipitation in East China
1
1
2
1
Rongshuo Cai , Hongjian Tan , Ronghui Huang , Cuihua Li
1
Key Laboratory of Global Change and Marine-Atmospheric Chemistry, Third Institute of
2
Oceanography, State Oceanic Administration, Xiamen, China, Center for Monsoon System Research,
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
In view of the pronounced interannual and interdecadal variations of sea surface temperature (SST)
and latent heat flux anomalies in East China Sea and its adjacent seas (ECS), which exhibit a clear
rising trend and have a significant impact on the marine environment, a regional climate model
(RegCM3) is used to examine the impacts of SST anomalies in ECS on East Asian atmospheric
circulation and precipitation in East China. Numerical experiment results clearly indicate that when
SST in ECS is above normal in summer, a downward motion with a divergence in the lower level and
a convergence in the upper level can appear over the middle and lower reaches and valley of Yangtze
River in East China and most of Northeast China, which contributes to the decrease in summer rainfall
in these areas, in addition to an upward motion with a strong convergence in the lower level and a
remarkable divergence in upper level over the region to the east of ECS. An upward motion with
strong convergence in the lower level and remarkable divergence in upper level also occurs in South
China, the southern part of Northeast China and the Korean Peninsula. Thus, there is an obvious
increase in summer precipitation in these regions. When SST in ECS is below normal, the opposite
phenomena appear in the above mentioned areas. Furthermore, the above simulated results and
relationship between the SST, latent heat flux anomalies in ECS and the interannual variations of
summer precipitation in East China are examined, based on HadISST, OAFlux3, NCEP/NCAR
reanalysis datasets, by using the methods of composite and correlation analyses. Therefore, it is
suggested that the thermal state of ECS in summer has obvious effect on East Asian atmospheric
circulation and rainfall in East China.
Page | 384
TU-59_B4.1
Multi-decadal change in the aridity of North China and its relationship to PDO
during 1900-2010
1
1
Cheng Qian , Tianjun Zhou
1
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
North China, which is located at the north edge of global moon area and as the political center and
one of the main industrial and agricultural production bases in China, has undergone a severe drying
trend since the 1950s. This trend is accompanying with the weakening of the East Asian Summer
monsoon over the recent decades. This study extends the investigation to examine the dry/wet
condition in North China to the whole period of 1900-2010 and the role of multidecadal variability
based on a self-calibrated Palmer Drought Severity Index (PDSI) data by applying an adaptive and
temporally local data analysis tool- the Ensemble Empirical Mode Decomposition (EEMD) method. A
secular transition from significant wetting to significant drying around 1959/1960 is found. About 70%
of the drying trend during 1960-1990 comes from a 50-70 yr multidecadal climate variability, which is
related to Pacific Decadal Oscillation (PDO) natural variability. The dry/wet condition in North China
has a good negative correlation with PDO, especially at 50-70 yr timescale. Their inverse relationship
is quite stable at multidecadal timescale, which has a good implication for 10-30 yr decadal prediction.
The possible mechanism behind the inverse relationship between dry/wet condition in North China and
PDO at multidecadal timescale is further explored using 20th century reanalysis data. The composite
differences between two positive PDO phases (1922-1945 and 1977-2002) and one negative PDO
phase (1946-1976) for summer reveal an anomalous EAP pattern meridional teleconnection along the
coastal East Asia controlling North Chin by anomalous high pressure and an anticyclone at mid-low
level, which are in favor of a dry condition.
Page | 385
TU-60_B4.1
Synchronization between lightning activity in Asia Maritime Continent and OLR
in Western Pacific Warm Pool and central-Africa
1
1
1
2
Yukihiro Takahashi , Yusuke Sanmiya , Mitsuteru Sato , Kozo Yamashita
1
2
Hokkaido University, Sapporo, Japan, Salesian Polytechnic, Machida, Japan
Lightning activity is an excellent proxy of atmospheric circulation in thunderstorm. However, there exist
no global lightning detection network which can observe lightning with a physical threshold. We
developed GEON, global ELF observation network, which can estimate charge moment change of
each lightning stroke and makes us possible to draw global lightning distribution map with a uniform
sensitivity over the world for the first time. We examined our first one-year dataset of lightning activity
in the period of August 2003 - July 2004, comparing OLR variations in the tropical regions, focusing on
about month periodicity.
It was found that, in the period from February to June 2004, the variation of the number of lightning
strokes in Asia Maritime Continent (hereinafter: MC) shows clear positive correlation with OLR in
Western Pacific Warm Pool (WPWP). In other words, when the thunderstorm activity in MC is
enhanced, the OLR in WPWPW becomes large, meaning less cloudy. On the other hand, OLR in
central-Africa, where the thunderclouds is main part of total cloud amount, shows negative correlation
with the number of lightning strokes in MC, implying the activities of thunderstorms both in centralAfrica and in MC oscillate in the same phase. Moreover, such one-month oscillations seem to be
synchronized with F10.7 index, the proxy of solar UV intensity.
Page | 386
TU-61_B4.1
Interannual variability of the summer Northeast Asian low
1
Zhongda Lin
1
LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
Many previous studies have addressed important role of synoptic cut-off lows in Northeast Asia (NEA)
on in-situ weather and climate variability in boreal summer. But understanding on summer-mean
circulation in this region is little. In this study the author identifies a climatological low geopotential
height center at 850 hPa over NEA downstream of the Mongolia highland. Interannual variability of the
NEA low (NEAL) is investigated by using the NCEP-NCAR reanalysis data during 1979-2010. Results
show when the NEAL is enhanced, it is characterized by near-barotropic negative geopotential height
anomaly over NEA. Moreover, the negative anomaly extends southward in the lower troposphere over
East Asia but with the positive anomaly in the upper troposphere. Associated with these circulation
changes, the rainfall increases and surface air temperature drops in NEA concurrent with the inverse
changes in the Yangtze River valley.
The NEAL's intensity is modulated by both tropical forcing and polar dynamics. The increased tropical
western North Pacific rainfall anomaly, through the Pacific-Japan (PJ) teleconnection pattern, induces
decreased geopotential height in NEA enhancing the NEAL. The tropical forcing explains the NEALrelated decreased rainfall in the Yangtze River valley and increased rainfall and dropped temperature
in the east of NEA. On the other hand, the Polar Eurasian (PEU) teleconnection pattern also triggers
decreased geopotential height in NEA in its negative phase. The polar dynamics results in the
increased rainfall in the west of NEA and the dipole pattern of temperature between NEA and the
Yangtze River valley.
Page | 387
TU-62_B4.1
Persistence and the change of Baiu precipitation anomalies
1
2,3
Tsuyoshi Yamaura , Tomohiko Tomita
1
2
RIKEN Advanced Institute for Computational Science, Kobe, Japan, Graduate School of Science
3
and Technology, Kumamoto University, Kumamoto, Japan, Research Institute for Global Change,
Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
This work examines the persistence and the change of interannual Baiu precipitation anomalies during
the Baiu season from late May to middle July around Japan. Atmospheric circulations affecting the
Baiu precipitation are abruptly changed around late June. In the former period, the sea surface
temperature anomalies (SSTAs) in the western North Pacific (WNP) associated with the El
Niño/Southern Oscillation (ENSO) mainly controls the Baiu precipitation anomalies through the
Pacific−East Asia teleconnection. The atmospheric circulations are characterized by specific surface
pressure anomalies induced by the Rossby wave response of the SSTAs, which persist for the former
period. On the other hand, the covariability of the SSTAs in the WNP and in the tropical Indian Ocean
(TIO) through the ENSO is crucial for the Baiu precipitation anomalies in the later period. Anomalous
atmospheric circulations are established through the Kelvin wave response from the TIO to the WNP.
This response controls the Baiu precipitation anomalies in the only later period because this response
needs a peculiar timing with the seasonal northward migration of the North Pacific subtropical high.
Thus, the interannual variations of the Baiu precipitation in these two periods have insignificantly
spatiotemporal correlations. These results suggest that detailed monitoring of SSTAs in both the WNP
and the TIO can improve the predictability of the Baiu precipitation in the entire Baiu season.
Page | 388
TU-63_B4.1
Southward shift of the South Asian high in response to anthropogenic forcing
1
1
1
Xia Qu , Gang Huang , Kaiming Hu
1
Institute of Atmospheric Physics, Beijing, China
The South Asian High (SAH) is a huge anticyclone in the upper troposphere. It is an important
component of Asia summer monsoon. The present study documents the change in the South Asian
High and the underlying precipitation under global warming, as well as the possible link between
changes, based on 17 Coupled Model Intercomparison Project Phase 5 (CMIP5) model simulations.
The CMIP5 historical simulation reasonably reproduces the upper-troposphere circulation (including
the SAH) the underlying precipitation, circulation and moisture.
Under global warming, the SAH shifts southward and more than 75% of the CMIP5 models projects
the movement. In individual model, the models showing stronger anticyclonic circulation in south part
of the climatological SAH than that in north part tend to project more significant southward movement
and vice versa. The underlying precipitation response displays a dipole feature: negative over the
southeastern equatorial Indian Ocean and positive over the tropical northern IO, the Bay of Bengal
and the equatorial western Pacific.
Using the linear baroclinic model (LBM), it is found that the forementioned regional rainfall changes
over the Bay of Bengal and the equatorial western Pacific mainly contributes to the southward shift of
the SAH. The precipitation and the surface wind over Indo-Pacific region are well coupled. On one
hand, the surface wind anomaly affects the rainfall response through altering the SST and moisture.
On the other hand, the LBM results show that the condensational heating released by regional rainfall
changes can sustain the surface wind response.
Page | 389
TU-64_B4.1
Asian monsoon and elevated heat pump mechanism in coupled aerosolclimate model simulations
1,2
3
1
4
5
Miriam D'Errico , C. Cagnazzo , P Fogli , W.K. M. Lau , J. Von Hardenberg
1
2
CMCC Euro-Mediterranean Centre for Climate Change, Bologna, Italy, University of Venice, Venice,
3
4
Italy, ISAC-CNR, Rome, Italy, Laboratory for Atmospheres, NASA Goddard Space Flight Center,
5
Greenbelt, United States, ISAC-CNR, Torino, Italy
A coupled aerosol-atmosphere-ocean-seaice model is used to analyse the relationship between
aerosol and the Asian summer monsoon. In this analysis the elevated heat pump hypothesis and the
solar dimming effect associated with aerosol loading are verified and are found to be consistent with
our simulations. When increased aerosol loading is found on the Himalayas slopes in the premonsoon period (April-May), an intensification in early monsoon rainfall over India is obtained. An
increase in rainfall and cloudiness during the early monsoon has a cooling effect on the land surface.
Here it is verified that this cooling is produced also through the solar dimming effect by the presence of
more dust from the deserts brought by an increased westerly flow in early monsoon season. A
subsequent reduction in monsoon rainfall over India is found, with a beginning of this decrease in
northern India. As these results, obtained with a fully coupled model, reproduce a reasonably realistic
pattern, it is possible to consider absorbing aerosols as a possible source of seasonal predictability of
the Asian summer monsoon over the Indian subcontinent.
Page | 390
TU-65_B4.1
Rainfall pattern in the middle of Indochina Peninsular during 2009-2010
summer monsoon
1
1
Nattapon Mahavik , Takehiko Satomura
1
Geophysics, Kyoto University, Kyoto, Japan
Rainfall patterns during summer monsoon in 2009 and 2010 in the middle of Indochina Peninsular
(ICP) are investigated using daily radar rainfall (DRR). The DRR is calibrated using rain gauge data
before proceeding to further analysis. The empirical orthogonal function (EOF) analysis applied to
DRR shows that the first three modes explain 40% of the total rainfall variance. The first mode shows
only positive value over the radar observation area with high value near the foot of Annam range in the
east of radar site. The second and third EOF show dipole patterns and explain 7% and 6% of total
variance, respectively. The Cumulative Density Function (CDF) is applied to the score of the EOF
results in order to find a physical meaning of EOF modes. A composite analysis of reanalysis data is
employed by selecting dates above and below 90% and 10% of CDF in each EOF modes. The first
and second modes are consistent with vorticity and wind directions. The third EOF mode indicates a
suppression of rainfall by topography.
Page | 391
TU-66_B4.1
The characteristics of longitudinal movement of the subtropical high in the
western Pacific in the pre-rainy season in South China
1
1
Hui Yang , Shuqing Sun
1
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
Associated with the anomalous longitudinal position of the subtropical high in the western Pacific
(SHWP) in the pre-rainy season in South China, the circulation anomalies greatly influence the
precipitation in the pre-rainy season in South China. When the SHWP is in a west position (WP), the
South China quasi-stationary front is stronger with more abundant precipitation there. However, when
the SHWP is in an east position (EP), a weaker front appears with a shortage of precipitation there.
There exists a good relationship between the longitudinal position of SHWP and SST in the tropical
region. A negative correlation can be found both in the central and eastern tropical Pacific and the
Indian Ocean. This means that the higher (lower) SST there corresponds to a west (east) position of
SHWP. This close relationship can be found even in the preceding autumn and winter. A positive
correlation appears in the western and northern Pacific and large correlation coefficient values also
occur in the preceding autumn and winter. A stronger eastern Asian winter monsoon will give rise to
cooler SSTs in the Kuroshio and the South China Sea regions and it corresponds to negative SST
anomaly (SSTA) in the central and eastern Pacific and positive SSTA in the western Pacific in winter
and the following spring. The whole tropical SSTA pattern, that is, positive (negative) SSTA in the
central and eastern Pacific and negative (positive) SSTA in the western Pacific, is favorable to the WP
(EP) of SHWP.
Page | 392
TU-67_B4.1
The role of peninsular India in the South Asian monsoon
1
2
Andrew Turner , Gill Martin
1
2
NCAS-Climate, University of Reading, Reading, United Kingdom, Met Office Hadley Centre, Exeter,
United Kingdom
Several studies have examined the role of the Tibetan Plateau and Himalayas in the initiation and
maintenance of the South Asian summer monsoon, but few have looked at the impact of the Indian
peninsula itself. In this study we describe the results of a series of novel experiments with the Met
Office Unified Model (HadGEM3) run in atmosphere-only configuration, in which the role of the Indian
peninsula is assessed. The contributions of the topography, orography and land surface properties to
the monsoon circulation and distribution of precipitation in the tropical Indo-Pacific region are
examined. While the model usually features a wet bias over the Western Ghats and Himalaya and a
dry bias over the northern part of the peninsula, initial results in experiments removing the Indian
peninsula and replacing it with sea surface boundary conditions suggest a large re-distribution of
precipitation in the northern Indian Ocean: the region at Indian longitudes featuring enhanced
precipitation. This may relate simply to the availability of moisture at the surface, however the diurnal
cycle of sensible heating will also be reduced in the absence of the land surface. In a further
experiment, the land surface characteristics of the peninsula are altered such that, while the land is
present, there are no limitations to the supply of moisture to the monsoon. We speculate that this will
help isolate the impact of the moisture constraint from that of the diurnal cycle of sensible heating.
Page | 393
TU-68_B7.2
Using MODIS fire radiative power and GOME-2 tropospheric NO2
measurements for deriving vegetation fire emission coefficients
1
1
2
1
Stefan Schreier , Andreas Richter , Johannes Kaiser , John Burrows
1
2
University of Bremen, Bremen, Germany, ECMWF, Reading, United Kingdom
Satellite measurements of fire radiative power (FRP) from the MODerate resolution Imaging
Spectroradiometer (MODIS) and nitrogen dioxide (NO2) from the Global Ozone Monitoring
Experiment-2 (GOME-2) are used to derive fire emission coefficients for different types of vegetation.
In a first step, monthly means of FRP have been analyzed for temporal correlation with monthly means
of tropospheric NO2 for five consecutive years from 2007 to 2011 on a 1° x 1° grid. The strongest
correlation is largely confined to tropical and subtropical regions which account for more than 80% of
yearly burned area on average globally. In these regions, the seasonal variation of fire intensity
expressed by the FRP data is reflected by the tropospheric NO2 columns to a high degree. In a next
step, spatially averaged regression coefficients were determined for five characteristic biomass
burning regions. The obtained regression coefficients are used for the prediction of tropospheric NO2
columns by simply applying a linear regression model. The best agreement between estimated and
observed tropospheric NO2 columns is found for the African regions north and south of equator with
large fraction of the NO2 signal being explained by the seasonal variability of FRP. By separating the
data according to land cover type, fire emission coefficients for different types of vegetation could be
derived. Retrieved fire emission coefficients for the dominating types of vegetation burned are 0.0221,
15
-4
-1
-2
0.02, 0.0191, 0.0186, 0.0131, and 0.0102 10 molecules 10 mW cm NO2 for wooded grassland,
broadleaf evergreen forest, cultivated crops, broadleaf deciduous forest and woodland, grassland, and
shrubs, respectively. However, the precedence of these values differs amongst the five selected
regions for certain vegetation types by a factor of up to three, calling into question the use of universal
emission factors in current bottom-up emission inventories.
Page | 394
TU-69_B7.2
A recommended approach to identify the sensitivity and importance of
parameters - the approach of conditional nonlinear optimal perturbation
(CNOP)
1
2
Sun Guodong , Mu Mu
1
2
LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China, Institute of
Oceanology, Chinese Academy of Sciences, Qingdao, China
It is costly to reduce all parameters errors in a numerical model through routine observation data or
additional observation data for better improving the simulation ability and forecasting skill. It is an
economical way just to gain some sensitive and important parameters values among all parameters. In
this study, an approach of conditional nonlinear optimal perturbation (CNOP) is employed to identify
which a parameter or a group of parameters is sensitive and important within the Lund-Potsdam-Jena
(LPJ) dynamical global vegetation model (DGVM) according to the effect of terrestrial ecosystem to
parameters in China. The most sensitive and important parameters among all parameters with the LPJ
model are picked up based on the maximal effect of terrestrial ecosystem using the CNOP approach.
Firstly, the CNOP approach and the sensitive analysis method are applied to identify the sensitivity
and importance of each parameter. The numerical results demonstrate that there are different to
identify each parameter sensitivity and importance using the CNOP approach and the sensitive
analysis method in arid and semi-arid region in China. Secondly, the further numerical results illustrate
that the most sensitive and important parameters using the CNOP approach are not the foremost
parameters that have been ranked using the two methods for the each parameter analysis in arid and
semi-arid region in China. The above results imply that nonlinear interaction among parameters plays
an important role in estimation of terrestrial ecosystem in arid and semi-arid in China. The numerical
results also suggest that the CNOP approach is recommended as to identify the parameters sensitivity
and importance, especially for the some parameters combination. And the CNOP approach could
provide some information to instruct us how to effectively observe or additionally observe in targeted
observation of parameters for the most sensitive and important parameters.
Page | 395
TU-70_B7.2
Atmogeochemical differentiation of elements in high-mountain landscapes the
Caucasus and Altai
1
Tatiana Kuderina
1
Institute of Geography Russian Academy of Sciences, Moscow, Russian Federation
Contemporary climate change intensifies matter migration in geosystems. High-mountain landscapes
that are subject to impact of transborder transfer of matter at regional and global levels are particularly
sensitive to these changes. The study of atmogeochemical migration of elements of high-mountain
landscapes in inland mountain systems of Russia is based on revealing the chemical composition of
air aerosol, air precipitation, and snow cover. Arid and semiarid plains of Eurasia are natural sources
of fine-dispersed aerosols. Increasing air temperatures caused an increase in the concentration of
dust and transboundary matter transfer. Large industrial centers and agricultural areas are
anthropogenic sources of air pollution. The study of snow cover in the Caucasus revealed that its
chemical composition includes typical lithogenic elements, such as Al, Si, Li, cyclic elements, such as
Na, Sr, Ba, and air-transferred elements, such as Th, Tl, Ga, As, Sb, W, Mo. The height of the
boundary layer can be as high as 4500 meters above sea level. The maximum mineral content is
typical of the western part of the Caucasus due to prevailing westerlies. The study of air aerosol
revealed elements of technogenic origin, such as Hg, Cd, Pb. In the Altai the aerosol contains global
elements, such as Ca, Sr, Ba. The maximum content of regional elements is found in western fronts
peaks of the Katunsky Range (Hg, Cu, Sn, Pb, Ni) that is likely related to industrial influence. It is
revealed that the mineral content of air precipitation increases in highlands towards inland. It is most
obvious in cases of air mass running via dry areas. The glacier retreat zone, which is subject to
intensive weathering, has an impact on the chemical composition of air precipitation as well.
Page | 396
TU-71_B7.2
Anthropogenic NOx emissions into the Arctic troposphere
1
1
1
1
Andreas Richter , Andreas Hilboll , Achim Zien , John P. Burrows
1
Insititute of Environmental Physics, University of Bremen, Bremen, Germany
Nitrogen oxides (NO + NO2) in the troposphere are key substances in the formation of photochemical
smog, contribute to the acidification of precipitation and can also act as nutrient when deposited into
surface waters.
Anthropogenic emissions of NOx dominate the total emissions in industrialised countries and also in
many parts of the developing world. Most NOx is emitted from fossil fuel burning for transport, heating,
and energy production, but locally also wildfires and burning of biofuels are significant contributors.
While NOx emissions in many industrialised countries have been declining over the last decade, large
increases are observed in industrialising countries and also in international shipping.
Polar Regions have so far been mostly unaffected by anthropogenic NOx which has a short
atmospheric lifetime and therefore is usually not transported to the Arctic or to Antarctica. However,
emissions from settlements close to the Arctic can sometimes be transported into the Arctic, providing
some influx of pollution. At the same time, intensified fossil fuel exploitation in Arctic regions as well as
the opening of the northern shipping routes in recent summers can enhance local NOx emissions.
In this study, satellite observations of NO2 are used to evaluate the relevance of both transport and
local emissions of NOx in the Arctic by investigating the fate of large NO2 pollution plumes from the
US and Europe as well as the temporal and spatial evolution of local emission hotspots.
Page | 397
TU-72_B7.2
The Geostationary Remote Infrared Pollution Sounder (GRIPS)
1
2
3
4
4
5
Russell Dickerson , John Burrows , Chad Fish , Larry Gordley , Marty McHugh , Mark Schoeberl
1
2
Dept AOSC. Univ. Maryland, College Park, United States, The University of Bremen, Bremen,
3
4
Germany, Space Dynamics Laboratory, Logan, United States, GATS Inc., Newport News, United
5
States, Science and Technology Corp., Lanham, United States
We describe a remote sensing instrument called the Geostationary Remote Infrared Pollution Sounder
(GRIPS) consisting of Gas Filter Correlation Radiometers (GFCR) targeting CO2, CO, CH4, and N2O.
These gases control changes in climate forcing and in atmospheric ozone. GRIPS (and a proposed
aircraft version) use GFCR that measures the following wavelengths: CO - 2.33, 4.64 µm; CO2 2.05µm; CH4 - 2.28µm; N2O - 3.88µm. In addition the column content of molecular oxygen is
measured with the O2 A-band at 076 µm to account for clouds and aerosols. Because the instrument
will look at reflected IR and thermal IR emissions it is sensitive to concentrations down to the Earth's
surface. Grips can measure column, contents, altitude profile, and diurnal cycles of these gases, all
with unprecedented precision and coverage. From these observations we can quantify sources, sinks,
fluxes, and export to improve dramatically our understanding of the global biogeochemical cycle of
carbon. GRIPS can also fingerprint the major source types including electricity generation,
transportation, and biofuels.
Page | 398
TU-73_B7.2
Megacities impact on air-quality and climate interaction in European region
1
2
1
Peter Huszar , Tomas Halenka , Michal Belda
1
2
Charles University, Prague, Czech Republic, Dept. of Meteorology and Environment Protection,
Charles University, Prague, Czech Republic
In regional scale, megacities affect significantly climate not only due to urban heat island but through
the complex interaction of atmospheric chemistry and aerosols with atmospheric processes as well,
especially radiative transfer and cloudness. These effects were extensively studied within the EC FP7
project MEGAPOLI, where we contributed with simulations using RegCM-CAMx couple for the region
covering most European megacities, i.e. industrial and urbanized areas.
In present study we have introduced urban parameterization into the previous simulations. The surface
scheme in regional climate model RegCM has been extended with Single Layer Urban Canopy Model
(SLUCM), which is used in dynamic scale within BATS scheme. The effect of this parameterization is
shown and discussed, sensitivity to some settings is presented. The impact of megacities at regional
scale in simulations is shown both for air quality and including interactive feedback to the climate.
Page | 399
TU-74_B7.3
Variations in the vertical distribution of ozone over northern India: role of
stratosphere-troposphere exchange and biomass burning
1
1
1
1
2
Narendra Ojha , Manish Naja , Tapaswini Sarangi , Rajesh Kumar , Shyam Lal , Harish C. Chandola
1
2
3
Atmospheric Science Division, ARIES, Nainital, India, PRL, Ahmedabad, India, Department of
Physics, Kumaun University, Nainital, India
3
Tropospheric ozone plays vital roles in the air quality degradation, atmospheric chemistry and climate
change. Space-borne observations have shown elevated levels of tropospheric ozone over the IndoGangetic Plain in the Northern India, however, lack of in situ measurements inhibit the validation of
satellite data and the understanding of underlying chemistry and dynamics. In view of this, balloonborne measurements of ozone vertical distribution and meteorological parameters have been made
using ozonesonde (EN-SCI 2ZV7 ECC) and radiosonde (iMet-1-RSB 403 MHz GPS), for a complete
o
o
seasonal cycle (2011), from a high altitude site Nainital (79.5 E, 29.4 N, 1958 m amsl) in the central
Himalayas. Maiden observations exhibit large day-to-day and seasonal variabilities in the ozone
distribution and meteorological parameters over this region. Tropopause pressure from radiosonde
observations generally agrees with the satellite (AIRS and TES) and model (WRF) but shows dramatic
variability (150-250 hPa) during winter and early spring. Lower tropospheric (2-6 km amsl) ozone
shows a prominent seasonality with highest levels during spring (~70-110 ppbv in May) and lowest
levels during summer-monsoon (~20-50 ppbv) which is consistent with the surface observations over
this region. However, ozone seasonality is less pronounced in middle-upper troposphere. Signatures
of stratospheric intrusions have been noticed during winter and are corroborated using observed
meteorology and model simulations (WRF-Chem). Springtime ozone profiles are classified using
MODIS fire counts and ozone levels are higher by 19.9 ± 4.6 ppbv in 2 to 4 km altitude range during
high fire activity period. Ozonesonde observations are in reasonable agreement with collocated
satellite (TES) retrievals; however, tropospheric columns from ozonesonde significantly differ from
TES during winter. It is suggested that regional photochemistry is the controlling process during spring
with a significant contribution from northern Indian biomass burning, while, dynamics including
stratospheric intrusions and advection play larger role during winter.
Page | 400
TU-75_B7.3
Impacts of ozone recovery and increase in greenhouse gases on the lower
stratospheric mean transport and eddy mixing
1
1
Makoto Deushi , Kiyotaka Shibata
1
Meteorological Research Institute, Tsukuba, Japan
Future changes in transport characteristics in the lower stratosphere are examined using multidecadal
simulations carried out with a chemistry-climate model (CCM) developed at the Meteorological
Research Institute (MRI-CCM). We conducted a control run from 1960 to 2100 under a prescribed
forcing in which both the greenhouse gas (GHG) and ozone depleting substance (ODS) vary
transiently in time, and two sensitivity runs in which either GHGs or ODSs are held fixed at 1960
levels. Comparing the two sensitivity runs with the control run, relative impacts of the ODS and GHG
forcings on the transport characteristics are analyzed, in which mean meridional transport and eddy
mixing are separately evaluated.
In the late 21st century, increasing of GHGs induce stronger residual circulation with enhanced eddy
transport in the mid-latitude lower stratosphere. The eddy transport is especially enhanced in the
northern hemisphere.
In the beginning of the 21st century, when the large ozone depletion is simulated in the Antarctic,
annually-averaged residual circulation and mean N2O transport for the control run are significantly
stronger and larger than the halogen-fixed run, especially in the Antarctic lower stratosphere.
Page | 401
TU-76_B7.3
Quantifying the role of orographic gravity waves in influencing polar
stratospheric cloud occurrence
1
1
2
3
Simon Alexander , Andrew Klekociuk , Adrian McDonald , Michael Pitts
1
2
Australian Antarctic Division, Kingston, Australia, University of Canterbury, Christchurch, New
3
Zealand, NASA Langley Research Center, Langley, United States
Polar Stratospheric Cloud (PSC) composition class information is extracted from the Cloud-Aerosol
Lidar with Orthogonal Polarization (CALIOP) curtains for four Antarctic PSC seasons (2007 - 2010)
and four Arctic PSC seasons (2006/07 - 2009/10). Orographic gravity wave (OGW) active days are
defined as those which have either wave-ice PSCs, or large Constellation Observing System for
Meteorology, Ionosphere and Climate (COSMIC) temperature variances. By combining the CALIOP
and COSMIC data with temperature and water vapour from the Microwave Limb Sounder (MLS), we
investigate the difference in PSC composition class occurrence as a function of the frost point
temperature for OGW-active and OGW-quiet days. The regions of direct impacts of OGWs on PSC
occurrence are defined using a trajectory model which follows particle movement from the ridge lines
over 24 hour periods. In the Arctic, data from Greenland, Scandinavia, Novaya Zemlya and Svalbard
are combined, whereas the Antarctic Peninsula is investigated separately. The results show
intermittent large wave activity above the mountain regions which is coincident with large increases in
water ice PSCs. These ice PSCs advect downstream, where increases in nitric acid trihydrate (NAT)
PSCs occur, supporting the mountain wave seeding hypothesis. We quantify the amount of different
PSC composition classes in the regions of direct impact due to OGW activity, and then calculate the
proportion of total polar-cap PSCs attributable to these mesoscale OGWs.
Page | 402
TU-77_B7.3
Evidence for STE over Easter Island (27S,109W)
1,2
1
Laura Gallardo , Adolfo Henríquez
1
2
Geophysics, Universidad de Chile, Santiago, Chile, Center for Climate and Resilience Research,
Santiago, Chile
Ozone soundings have been performed on Easter Island (27ºS, 109ºW, 51 m.a.s.l.) since 1995 as part
of the Global Atmospheric Watch (GAW) program of the World Meteorological Organization (WMO). In
this work, we analyze 186 soundings performed on Easter Island over the period 1995-2010. We
characterize ozone profiles over this remote area of the Pacific by means of statistical analyses that
consider, on the one hand, a traditional climatology that describes the data in terms of seasonal and
annual cycles, and, on the other hand, a more process oriented analysis based on clustering
techniques, and self-organizing maps. We show evidence for stratosphere-troposphere exchange in
connection with deep troughs and the presence of the subtropical jet stream, particularly during winter
and spring.
Page | 403
TU-78_B7.3
Variability in the stratospheric aerosol load from SCIAMACHY limb-scatter
observations
1
1
1
2
1
Lena A. Brinkhoff , Florian Ernst , Alexei Rozanov , Christian v. Savigny , René Hommel , Claus
1
1
1
Gebhardt , Heinrich Bovensmann , John P. Burrows
1
2
Institute of Environmental Physics (IUP), University of Bremen, Bremen, Germany, Ernst-MoritzArndt-University of Greifswald, Greifswald, Germany
Stratospheric aerosols are of scientific interest, as they primarily scatter solar radiation, and therefore
increase the Earth´s planetary albedo. The permanent aerosol background in the stratosphere is due
to tropical injection of tropospheric air containing SO2, COS, and sulphate particles, which are
precursors for stratospheric aerosols. An additional contribution is sporadically caused by an uplift of
SO2 after a strong volcanic eruption. Especially after strong volcanic eruptions, the consequential
effect of stratospheric aerosols on the Earth´s radiation budget is stratospheric warming and
tropospheric cooling. Furthermore, they have an impact on stratospheric chemistry: Stratospheric
aerosols are precursors for polar stratospheric clouds and thus support the destruction of ozone inside
the polar vortex. They even lead to a halogen-driven ozone destruction outside polar vortices. On
account of these properties, stratospheric aerosols belong to the so-called Essential Climate
Variables.
Observations were supplied by SCIAMACHY, which was one of ten instruments onboard the
ENVISAT spacecraft, detecting the sunlight in the wavelength range from 214 to 2386 nm with three
different viewing geometries: nadir, limb and occultation. Limb-scatter measurements have the
advantage of high vertical resolution, compared to nadir measurements, and a near-global coverage
on the dayside of the Earth, in contrast to solar occultation measurements. The present SCIAMACHY
limb aerosol product from Aug. 2002 to April 2012 (loss of ENVISAT) will be presented. It shows, for
example, signatures of volcanic eruption and bushfire events in the tropopause region. Furthermore, at
about 27 km altitude, we observe a very pronounced seasonal cycle in the aerosol load, which is
mainly caused by the Brewer-Dobson Circulation and at about 32 km altitude a biennial variation in the
aerosol load becomes apparent due to the QBO.
Page | 404
TU-79_C4.1
Regional difference in altitudinal dependency of snow depth with highresolution dynamical downscaling
1
1
1
1
1
Fumichika Uno , Hiroyuki Kawase , Noriko N. Ishizaki , Takao Yoshikane , Fujio Kimura , Tsutomu
2
2
Iyobe , Katsuhisa Kawashima
1
2
Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan, Research Institute for
Natural Hazards and Disaster Recovery, Niigata University, Niigata, Japan
The reproducibility of the snow cover in the mountain areas depends on the horizontal resolution of a
climate model. A high-resolution experiment can simulate detailed snow cover distributions and their
characteristics, i.e., the relation between the amount of snow cover and the altitude of the terrain.
Then, we discussed the factors of reproducibility of snow cover distributions and the regionality of
altitudinal dependency using dynamical downscaling with 1.5km horizontal resolution.
We used the Advanced Research Weather Research and Forecasting (WRF) modeling system
Version 3.4. The initial and lateral boundary conditions are interpolated from the ERA-interim data set.
We used the Noah-LSM including a one-layer snow model as a land surface model.
The snow depth tend to be underestimated by the model, however the characteristics of regionality of
snow is consistent with the observations having sufficient reproducibility. The altitudinal dependencies
with linear and nonlinear relationships are simulated in the windward side and the leeward side of the
coastal mountainous area, respectively. In the experiment, many snow clouds are blocked by the
coastal mountain about 1,000m, resulting in the difference of snowfall between windward and leeward
sides. The sensitivity experiment without the coastal mountain shows the nonlinear altitudinal
dependency in leeward side makes similar to the linear dependency in windward side. As the results,
the geometry of terrain is the major factor in regional difference of the altitudinal dependency.
Page | 405
TU-80_C4.1
Precipitation forcing fields for the Alpine region: methods and insights from a
new trans-national dataset
1
1
1
Francesco Isotta , David Masson , Christoph Frei
1
Federal Office of Meteorology and Climatology MeteoSwiss, Zurich, Switzerland
The increased use of distributed models in environmental research calls for spatially comprehensive
datasets of meteorological parameters. Preferably, such forcing fields are represented on a regular
grid. Existing grid datasets for the Alps are often constrained to national territories, or they are of
comparatively coarse resolution. To foster distributed modelling and trans-national climate research, a
new gridded precipitation dataset has been developed. It covers the entire Alpine region (sectors from
seven countries), makes use of rain-gauge data from high-resolution national networks (more than
6000 stations), and expands over 38 years (1971-2008) at a daily time resolution. Our presentation
introduces the comprehensive station data used for this new dataset, it elaborates on the method of
spatial analysis employed, and discusses the potential and limitations of the dataset for distributed
modelling. We also illustrate insights on the Alpine precipitation climate that were gained from the new
dataset, with an emphasis on indicators for heavy precipitation and long dry periods. The gridded
dataset will be made available for scientific use. This study is part of EU project EURO4M and
expands from previous research on the Alpine precipitation climate at ETH Zurich.
Page | 406
TU-81_C6.2
Influence of tensile strength and weak layer heterogeneity on slab tensile
failure propensity
1
1
1
Gaume Johan , Chambon Guillaume , Eckert Nicolas , Naaim Mohamed
1
IRSTEA, Grenoble, France
1
The evaluation of the position of slab tensile rupture represents an important concern for the
evaluation of the avalanche release area and hence hazard assessment. In this study, a mechanicallybased statistical model of the slab-weak layer system accounting for weak-layer heterogeneity, stress
redistribution by elasticity of the slab and the slab possible tensile failure is simulated. Two types of
avalanche releases are distinguished in the simulations: (1) full slope releases, where the entire
simulated slope is released and the heterogeneity is not sufficient to trigger a tensile failure within the
slab; (2) partial slope release, where tensile failure occurs within the slab due to the heterogeneity so
that only a part of the slope is released. We present the proportion of these two release types as a
function of the different model parameters obtained from finite element simulations, and a simple
statistical model capable of reproducing these results. One of the main outcome is that, for slab tensile
strength σT higher than the average cohesion < c >, all the releases appear to be full-slope,
highlighting the critical and major influence of morphological features such as rocks, trees, slope
curvature and ridge, as already pointed out in the litterature. It is also shown that the partial slope
releases percentage is significantly increased when the slab depth h is of the same order than the
correlation length ε and when the standard deviation of cohesion σc increases. Finally, phase diagrams
of partial slope release percentage are computed to stress out the complex influence of the different
parameters involved.
Page | 407
TU-82_C6.2
Terrestrial radar measurements of Alpine snow slopes
1
1
1
Andreas Wiesmann , Rafael Caduff , Jessica Papke , Tazio Strozzi
1
GAMMA Remote Sensing AG, Gumligen, Switzerland
1
Remote sensing of snow with active and passive microwaves has a long tradition. Terrestrial
instruments are used to investigate the interaction of snow with microwaves at selected locations,
while air- and space-borne sensors are used to image a larger area. With the proposed explorer
mission CoReH2O, a satellite dedicated to cryospheric applications is in evaluation at ESA. While the
terrestrial instruments are usually doing point measurements, the satellite based instruments have
defined observation geometry and observation schedule. These constraints hamper the potential to
investigate dynamic processes in the snowpack spatially, especially of slopes. Terrestrial imaging
radars such as the GPRI (GAMMA Portable Radar Interferometer), overcome some of these
constraints due to their portability and image acquisition time of about 30 seconds and the possibility
to do repeat acquisitions within minutes.
In our presentation we discuss results of campaigns conducted in the Swiss Alps covering dry and wet
snow conditions as well as measurements before and after an artificial avalanche release. The
investigation covers the analysis of backscatter information spatially and in time as well as the
interferometric analysis of the corresponding time series. The interferometric processing allows to
gather information on the temporal decorrelation within the snowpack and to retrieve spatial
displacement information. The interferometric decorrelation is linked with the snowpack structure, a
drop in coherence is an indicator for change in the snowpack. Such a change can be induced by short
term effects like an avalanche release or skiers, or long term degradation due to snow metamorphosis.
If the correlation between two image acquisitions is high the interferometric phase can be interpreted.
The phase reveals information about the displacement of the target area (e.g. speed and extent of
creeping snow) along the line of sight, as well as changes in the atmospheric conditions.
Page | 408
TU-83_C6.2
Detection and characterization of weak layers
1
1
1
1
Bernadette Köchle , Margret Matzl , Martin Proksch , Martin Schneebeli
1
WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
The microstructure and the stratigraphy of a snowpack determine its physical behavior. What is
considered a layer or a structural transition depends on the physical problem in question. For the
mechanical stability of a snowpack the stratigraphic order of stiffness determines the amount of
mechanical stress the snowpack is able to support. A key factor in the formation of dry snow slab
avalanches is the presence of a buried weak layer, which has less strength and fails easier than the
others. To detect potential weak layers in a snowpack it is essential to find an objective structural
parameter that is an indicator of a relevant microstructural change.
During two winter seasons, we casted natural weak layers and their adjacent layers in the field and
scanned them non-destructively with X-ray computer tomography with a resolution between 10 - 20
µm. From the reconstructed three-dimensional model of the layered sample, the variation of structural
properties over the centimeter-sized sample can be calculated and visualized. We found that
geometrical properties like density or grain size do not always reflect structural transitions. In order to
quantify the relative differences in stiffness on a microstructural scale, we calculated the Young's
modulus of the individual layers by voxel-based finite element simulations. The correlation between
microstructural parameters and stiffness was also investigated.
Page | 409
TU-84_C6.2
Deriving snow stability from the snow micro-penetrometer signal
1
1
Benjamin Reuter , Jürg Schweizer
1
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland
Snow stability is usually estimated from field data by interpreting snow profiles or stability test results.
Both methods, however, are slow and require experience. The snow micro-penetrometer (SMP), on
the other hand, allows measuring the penetration resistance objectively and quickly; it provides data
on the vertical structure of the snow cover. So far, exploiting the SMP signal in terms of snow stability
is missing. Given our present understanding of dry-snow slab avalanche release, a mechanics-based
measure of stability should provide an estimate of the propensity of a weak layer and its overlaying
slab to initially fail and eventually favour crack propagation. Micro-structural information on the
stratified snow cover measured with the snow micro-penetrometer forms the basis for the stability
evaluation. The stiffness of a layered slab, considered as a laminate, and the specific fracture energy
of the weak layer are derived. These two quantities are key to estimate the crack propagation
propensity, i.e. the critical cut length. In addition, the proposed algorithm also takes into account the
fracture initiation process prior to crack propagation by considering slab stiffness as well as
compression of slab layers. We calibrated our algorithm with field experiments, such as compression
and propagation saw tests. Results show that the proposed algorithm has the potential to predict
stability from penetration resistance profiles - based on the mechanical behaviour of the snow cover.
We will apply our mechanics-based snow stability approach to understand the influence of the spatial
distribution of snow properties on avalanche formation at the slope and basin scale.
Page | 410
TU-85_C6.2
Towards a new chain of models for avalanche hazard forecasting in French
mountain ranges, including low altitude mountains
1
1
1
2
2
Matthieu Lafaysse , Samuel Morin , Cécile Coléou , Matthieu Vernay , Damien Serça , François
3
1
1
1
Besson , Jean-Marie Willemet , Gérald Giraud , Yves Durand
1
2
CNRM-GAME/CEN Météo-France/CNRS, Saint Martin d'Hères, France, Ecole Nationale de la
3
Météorologie, Toulouse, France, DCLIM/AVH, Météo-France, Toulouse, France
Operational avalanche hazard warning carried out by Météo-France for the three main mountain
ranges (Alpes, Pyrénées, Corsica) have used snow simulations based on the SAFRAN-CrocusMEPRA (SCM) model chain, for over a decade. The meteorological analysis tool SAFRAN provides
estimates of the atmospheric conditions by elevation steps of 300 m in meteorological homogenous
massifs. Crocus computes the evolution of the physical properties of snow using SAFRAN inputs, for a
variety of slopes and aspects within each massif and altitude band. MEPRA is used to diagnose the
associated avalanche hazard. Mid-altitude mountain ranges (Massif-Central, Vosges, Jura),
culminating below 2000 meters, were until now not considered. Although they rarely experience strong
avalanche crises, in such cases the forecasters in charge of avalanche hazard bulletins didn´t have
any operational tool to assist them in analyzing and forecasting snow conditions. Forecasting
snowmelt floods is also an episodically strong concern in such areas.
Crocus has recently been incorporated in the Earth surface platform “SURFEX” as one of the
snowpack schemes of the land surface model ISBA. This allows in particular to explicitly represent
interactions between snow and the underlying soil. Such an improvement makes possible to use
Crocus under conditions where the state of the soil may have a significant impact on the properties of
snow, which is particularly true for low-altitude regions, where the snowpack is shallower and more
ephemeral. A new version of the SCM model chain, renamed SAFRAN-SURFEX-MEPRA should
replace SCM for all operational applications in the near future.
Here we present a comprehensive evaluation of the performance of this new model chain, not only for
Alpes, Pyrénées and Corsica, but also for mid-altitude mountain ranges. Models are evaluated against
ground-based measurements of snow depth, snow water equivalent and snowpack profiles gathered
at over 150 locations in all considered mountain ranges.
Page | 411
TU-86_C6.2
The elasticity tensor of seasonal snow
1
2
2
Henning Löwe , Jonah H. Lee , Liangbiao Chen
1
2
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland, Mechanical
Engineering, University of Alaska Fairbanks, Fairbanks, United States
The macroscopic elasticity tensor, one of the most fundamental material properties of snow as a
random material, is important in various applications. Notably, current theories of fracture nucleation
for slab avalanche release require an elastic modulus of the slab as input. While an effective modulus
can always be estimated from crack propagation tests in the field, its relation to zero-frequency
elasticity remains unclear. Elastic measurements of snow are notoriously difficult as a result of the
peculiar visco-plastic properties of ice as its constituent material.
To better constrain the fracture nucleation theory e.g. by validating measured moduli, it would be
desirable if elastic quantities can be independently predicted by microscopic simulations. To this end,
we conduct purely elastic finite element simulations of snow based on tomography data, and
characterize the elasticity tensor for various seasonal snow types. In view of the problem of slab
characterization, we assess whether macroscopic elasticity can be related to microstructural
parameters which allow for a simpler retrieval in the field. To gain confidence in the simulations, we
also consider their validation by experimental means. To this end, we assess the potential of 3D
printing technology by creating snow prototypes with replicated microstructure but with substituted
constituent material which is mechanically more convenient.
Page | 412
TU-87_C6.2
A relative differences approach to detect weak layers in simulated snow
profiles
1
1
Fabiano Monti , Jürg Schweizer
1
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland
Snow cover simulations have the potential to increase the spatial and temporal resolution of snow
stratigraphy information. However, to be useful for avalanche forecasting, snow cover stability
estimates from the stratigraphy simulations are needed. In particular, detecting the weak layer and
thus defining the slab thickness within a simulated snow profile is among the key information for
evaluating snow stability. The threshold sum approach (TSA) is a semi-quantitative method developed
to detect potential weaknesses within the snowpack. It analyses key parameters (e.g. grain size, grain
type, hardness) that are related to snow instability, if reported in their respective critical range. Using
relative differences and values instead of an absolute measure (e.g. not considering how soft a snow
layer is, but rather how soft it is compared to the weighted average value of the profile) avoids possible
inconsistencies due to differences in observation techniques or due to varying definitions of
parameters in simulated and manually collected data. We tested a relative differences approach
(RDA) on snow profiles simulated with the 1-D snow cover model SNOWPACK. The characteristics of
the weak layers found with compression tests in 83 manual profiles were compared with the
characteristics of potential weak layers detected by TSA and RDA in the corresponding simulated
profiles. Simulated weak layer characteristics agreed reasonably well with the observations. With RDA
potential weak layers were slightly better detected as with TSA, which was modified to be applied to
simulated profiles. Implementing RDA in SNOWPACK instead of TSA would not require refining the
thresholds values whenever the model is revised and thus be a more robust method for stability
interpretation.
Page | 413
TU-88_C6.2
Reconstructing the causes of snow avalanches in March 1988 in Fagaras
Mountains (Area Suru - Negoiu), Romania
1
2
3
3
Anca Victorina Munteanu , Narcisa Milian , Laura Comanescu , Alexandru Nedelea
1
2
University of Bucharest, Faculty of Geography, Brasov, Romania, Regional Service of Weather
3
Forecast Sibiu, National Meteorological Administration, Sibiu, Romania, Faculty of Geography,
University of Bucharest, Bucharest, Romania
In Romania during communism, informations about avalanches could be found more difficult (just from
foreign magazines). However, climbers who reach the exposed mountain areas knew the occurrence
conditions of avalanches. Furthermore, sports competitions were held and many managed to complete
the routes. However, accidents due to unexpected avalanches took place. The present study aims to
present the reconstruction of some avalanches caused by a group of seven climbers athletes in
Fagaras Mountains (Southern Carpathians, Romania), in the Suru - Negoiu peaks area. The restoring
of the local conditions was made through the analysis of the details described in a book by the coach
climbers and through interviews with the heroes of the book. The result was the reconstruction of the
local conditions along the path followed by the climbers and of the place in which occurred several
avalanches. The biggest one was on the southern slope of Negoiu Peak (2,535 m, the second highest
in the Romanian Carpathians) and covered two of the climbers which were rescued by teammates.
Also, dates obtained from weather station Balea archive were analyzed (in the same mountain massif)
to study the snow conditions and avalanches risk at the time.
This study tries to complete historical data (relatively few in number) about known avalanches which
occurred in the Romanian Carpathians.
Page | 414
TU-89_C6.2
The study of snow avalanches from a climate change perspective
1
2
2
1
3
Paola Dellavedova , Valerio Segor , Luca Pitet , Eloise Bovet , Walter Steinkogler , Jochem
3
3
4
5
5
Veitinger , Jim McElwaine , Margherita Maggioni , Maria Cristina Prola , Secondo Barbero , Igor
6
3
Chiambretti , Betty Sovilla
1
2
Fondazione Montagna Sicura, Quart, Italy, Regione Autonoma Valle d'Aosta, Regione Autonoma
3
4
Valle d'Aosta, Quart, Italy, SLF, Davos, Switzerland, Università di Torino - NATRISK, Torino, Italy,
5
6
ARPA Piemonte, Torino, Italy, AINEVA, Trento, Italy
In the last thirty years an increase in air temperatures, a possible increase of extreme rainfall events
and an altitude increase in the snowline have been observed. These changes influence the snowpack
and will therefore change the type, magnitude, frequency and dynamics of avalanches. Currently we
cannot assess the influences of these changes on avalanche dynamics, due to the lack of dynamics
models, which include the influence of the snowpack properties.
The STRADA project was founded in 2010 to fill this gap and to develop strategies for adaptation of
the management of natural risks to climate changes in Switzerland and Italy.
The project includes the development of methodologies for the study of frequent avalanches in a
changing climate context. These methodologies combine the most advanced knowledge in the field of
modelling avalanche dynamics and simulating the evolution of the snow. They will be used in risk
mitigation strategies, such as transport links and ski-resorts management.
During the project, many measurements were made at the experimental sites: mass, speed, flow
regimes and runout distances of numerous avalanches were recorded. The corresponding snowpack
characteristics were directly measured in the field or indirectly determined using the numerical model
SNOWPACK.
The combined analysis of this data has shown, for the first time, the importance of the variation of the
snowpack temperatures along the avalanche track on the avalanche dynamics and therefore on the
runout distance. This analysis has also shown how the distribution and height of the snowpack can
change the effective ground morphology, changing particularly the effective roughness, with a direct
influence on the location and extent of the avalanche starting zones. These new findings will be
implemented in RAMMS, an avalanche dynamics model, which takes into consideration, in addition to
the erosion processes, the characteristics of the snowpack, including its temperature.
Page | 415
TU-90_C6.3
The chance of RAMMS to simulate the small avalanche triggered at the
Seehore test site on 2011.03.05
1,2
3
4
2
3
Eloïse Bovet , Margherita Maggioni , Perry Bartelt , Bernardino Chiaia , Michele Freppaz
1
2
Fondazione Montagna sicura, Courmayeur, Italy, DISEG, Politecnico di Torino, Torino, Italy,
3
4
DISAFA, Università di Torino, NatRisk-LNSA, Grugliasco (TO), Italy, WSL-SLF, Davos, Switzerland
Avalanche dynamics models are widely used to simulate extreme avalanches for hazard mapping
purposes; they are well developed and calibrated on numerous real events. Only recently have small
avalanches been studied, mainly for problems related to the safety of ski runs and roads. Small
avalanches are extremely difficult to simulate with classical avalanche dynamics models, which are
based on simplified physics and calibrated parameter sets. New models have begun to describe many
of the physical processes occurring within an avalanche flow, including snow entrainment, granular
turbulence, flow regime transitions and variable flow density. In this work we use one of these newly
developed models, RAMMS, to back-calculate a small, well-documented avalanche artificially
th
triggered on the 5 of March 2011 at the Italian experimental test site of Seehore in Aosta Valley. The
back-calculation procedure, using data obtained by field work, laser scan measurements and video
analysis, lead us to find a set of model parameters that allow RAMMS to reproduce with high accuracy
the real event. We highlight the fact that (1) it was not possible to reproduce the event without having a
high-resolution digital terrain model of the avalanche track (2) snowcover erosion and deposition
processes must be included in the model formulation and (3) constant friction parameters could not
reproduce avalanche stopping. Our results indicate that flow friction appears to be a physical process
controlled by random granular interactions and therefore highly dependent on snow temperature and
3
snow granulometry. We stress here the release volume of the considered avalanche: only 200 m . We
therefore pose the question of how avalanche dynamics models will be used in the future. This work
3
was possible thanks to the project "MAP - Monitoring for the Avalanche Prevision, Prediction and
Protection”.
Page | 416
TU-91_C6.4
Snow avalanche activity, risk and hazard mapping in Khibiny Mountains (NW
Russia): сhallenges and ways forward
1
1
Yuliya Zaika , Marina Vikulina
1
Khibiny Educational and Scientific Station of the Faculty of Geography, Lomonosov Moscow State
University, Kirovsk, Russian Federation
Khibiny Mountains is an area within the arctic territory of Russia with the increasing exploitation of its
natural resources and the seasonal snow being the main indicator of climate changes. Thus, this area
is highly vulnerable to all predicted changes in terms of local population, economics, environment and
industry which are the subjects to mountain hazards.
The region is highly developed due to the infrastructure and transportation systems related to the
urban constructions, current, suspended and new mines along with the rapidly growing winter
recreation component whether it is ski complexes or individual touristic areas.
To evaluate individual avalanche risk the parameters of avalanche activity (frequency of avalanches,
duration of the avalanche-prone period) and socio-economic parameters of people's vulnerability were
taken under consideration. High degree of avalanche hazard obviously occurs within the zones of ski
complexes and major transportation lines as well as within the territory of the settlements and
industrial areas. Results of assessment and mapping of individual avalanche risk show that acceptable
-6
risk level (less than 1*10 ) prevails for the most part of Khibiny Mountains. Areas with admissible and
unacceptable individual avalanche risk prevail at the south-east part where settlements, ski complexes
and minings are located. High values of individual avalanche risk are common for ski mountaineering
areas. The most part of Khibiny ski complexes is located within avalanche-hazardous slopes.
Integrated estimation of avalanche activity, hazard and risk was introduced for the study area for the
first time.
However, the lack of modern and innovative approaches to snow avalanche mapping in the region is
the most important challenge along with the poor reporting on avalanche situation. Due to the
increasing industry and touristic activity, the up-to-date picture of avalanche situation in the area is
needed together with the informative reporting to the local community and government.
Page | 417
TU-92_C6.4
Snowcatcher: retarding avalanches in motion with net structures. A question of
mesh size?
1
1
Engelbert Gleirscher , Jan-Thomas Fischer
1
BFW - Institute for Natural Hazards, Innsbruck, Austria
Steel wire rope nets have become common as a protection measure against avalanches in Europe by
preventing a release in the potential starting zone. A novel approach is to retard the movement of an
avalanche after it has been initiated. A full scale structure, the Snowcatcher, was installed and
instrumented with several load measuring pins, which record the dynamic loads caused by an
avalanche. These measurements are the motivation to particularly observe the influence of net
structures to snow avalanches. In the laboratory scaled granular experiments were performed in two
set-ups. In the first set-up the influence of the net barrier angle, in the second set-up the mesh size is
investigated. Measuring front velocities and flow depths in the experiments, the study indicates two
values with important influence on the net structures effectivity: The mesh size and the velocity of the
granular flow. Experiments with different net barrier angles showed that nets perpendicular to the flow
direction lead lower effectivities than inclined nets. Experiments with different mesh sizes indicate a
velocity dependency on the effectivity at a certain ratio of mesh to grain size. Smaller mesh sizes in
the range of the maximal particle grain size lead to the plugging of the net. They act similar to a solid
barrier and obtain therefore best effectivity disregarding overflows. For large mesh sizes the effectivity
of the net barrier is increasing with increasing velocity of the flow.
Page | 418
TU-93_C6.4
Calculating snow avalanche runout distances using empirical methods and
RAMMS for avalanche hazard zoning in Russia
1
Alla Turchaninova
1
Laboratory of Snow Avalanches and Debris Flows, Faculty of Geography, Lomonosov Moscow State
University, Moscow, Russian Federation
Snow avalanche runout distances and their return period assessment is an essential part of avalanche
hazard zoning and snow engineering. A lot of one-dimensional empirical methods for calculating
«maximum» avalanche runout distances based on topographic parameters of avalanche tracks were
performed by snow engineers for different mountain regions of Russia. However, in many cases it is
not possible to apply commonly accepted methods for avalanche zoning needs due to poor data
availability. We discuss this problem by applying different Russian well known empirical methods for
several avalanche test sites in the Khibini Mountains (The Kola Peninsula) and the Caucasus.
The most accurate and well-documented data of powder and wet, big rare and small frequent snow
th
avalanche events have been collected since 1960 till today in the Khibini Mountains by the
Avalanche Safety Center of “Apatit” and in the Caucasus by the Faculty of Geography, Moscow State
University. These data were digitized and put into the detailed large-scale avalanche database (GIS).
It contains contours of observed avalanches (more than 50 years of observations), DEMs, remote
sensing data, snow pits, photos etc. Thus, this information and the runout calculating results are
unique sources for understanding avalanche flow rheology and future development of empirical
methods and avalanche dynamics models.
А new statistical approach to assess the avalanche runout distance return period based on avalanche
release zones clustering was developed using GIS. We applied Swiss computer model RAMMS to
simulate well-documented avalanches and discuss the calibration of the avalanche model friction
coefficients in function of the geographical conditions of the mountain region. However, avalanche
hazard zoning is not yet used by land planning authorities in Russia. Our approach can be used for
the future development of avalanche zoning in Russia.
Page | 419
TU-94_C6.4
Measurements at Seehore test site in winters 2010/2011 and 2011/2012
1
1
1
1
2,3
Monica Barbero , Fabrizio Barpi , Mauro Borri-Brunetto , Eloïse Bovet , Elisabetta Ceaglio ,
1
1
3
1
3
Bernardino Chiaia , Valerio De Biagi , Michele Freppaz , Barbara Frigo , Danilo Godone , Margherita
3
1
4
3
Maggioni , Oronzo Pallara , Valerio Segor , Davide Viglietti
1
2
DISEG, Politecnico di Torino, Torino, Italy, Fondazione Montagna Sicura, Courmayeur, Italy,
3
4
DISAFA and NatRisk-LNSA, Università di Torino, Torino, Italy, Assetto idrogeologico dei bacini
montani - Assessorato Opere pubbliche, difesa del suolo e edilizia residenziale pubblica, Regione
Valle d'Aosta, Aosta, Italy
Seehore test site is a new experimental test site in Aosta Valley at a real scale devoted to the study of
the dynamics of small and medium snow avalanches, the release processes and the interaction
between avalanche flows and obstacles. Running from winter 2009-2010 with ALCOTRA - Obiettivo
Cooperazione territoriale europea Italia - Francia (Alpi) 2007 / 2013, DynAval "Dynamique des
avalanches: départ et interactions écoulement/obstacle" (and now with project MAP3 “Monitoring for
the Avalanche Prevision, Prediction and Protection” ) - Assetto idrogeologico dei bacini montani Assessorato Opere pubbliche, difesa del suolo e edilizia residenziale pubblica - Regione Valle d´Aosta
fundings, the spontaneous and artificially triggered avalanche events of the first winter seasons served
as tests for setting the devices that have been installed on an instrumented structure placed along tne
track, to measure the impact forces of the avalanche flows. Loads cells supporting an adjustable set of
plates, accelerometers, thermocouples and a pressure gauge are connected to a recording unit and
data are stored. In parallel, snowpack properties in the release zone are evaluated with direct
measurements and deposit extension and characteristics are measured. Laser scanning is performed
before and after an avalanche event for the determination of the erosion and deposition volumes.
Avalanche front velocity is estimated by videogrammetry. We analyzed the database in order to find
possible relations between the snowpack properties and the avalanche characteristics. The results of
the operative winter seasons 2010/2011 and 2011/2012 are presented and a preliminary data analysis
is made.
Page | 420
A4.2e - Sea ice and Ocean-Atmosphere Interactions
10.07.2013 08:15-09:45, Sanada II
156
Arctic and Antarctic sea ice and climate
1
2
Sandra Barreira , Ted Scambos
1
Meteorology, Argentina Naval Hydrographic Service, Ciudad Autonoma de Buenos Aires, Argentina,
2
National Snow and Ice Data Center, Boulder, United States
Principal Components Analysis in T-Mode Varimax rotated was performed on Antarctic and Arctic
monthly sea ice concentration anomalies (SICA) fields for the period 1979-2012, in order to investigate
which are the main spatial characteristics of sea ice and its relationship with atmospheric circulation.
This analysis provides 5 patterns of sea ice for winter-spring period and 3 patterns for summer-autumn
for Antarctica (69,2% of the total variance) and 3 different patterns for summer-autumn and 3 for
winter-spring season for the Arctic Ocean (67,8% of the total variance). Each of these patterns has a
positive and negative phase. We used the Monthly Polar Gridded Sea Ice Concentrations database
derived from satellite information generated by NASA Team algorithm. To understand the links
between the SICA and climate trends, we extracted the mean pressure and, temperature field patterns
for the months with high loadings (positive or negative) of the sea ice patterns that gave distinct
atmospheric structures associated with each one. For Antarctica, the first SICA spatial winter-spring
pattern in positive phase shows a negative SICA centre over the Drake Passage and north region of
Bellingshausen and Weddell Seas together with another negative SICA centre over the East Indian
Ocean. Strong positive centres over the rest of the Atlantic and Indian Oceans basins and the
Amundsen Sea are also presented. A strong negative pressure anomaly covers most of the Antarctic
Continent centered over the Bellingshausen Sea accompanied by three positive pressure anomalies in
middle-latitudes. During recent years, the Arctic showed persistent associations of sea-ice and climate
patterns principally during summer. Our strongest summer-autumn pattern in negative phase showed
a marked reduction on SICA over western Arctic, primarily linked to an overall increase in Arctic
atmospheric temperature most pronounced over the Beaufort, Chukchi and East Siberian Seas, and a
positive anomaly of pressure over Greenland.
Page | 421
332
Vertical heat advection below shear lines: a mechanism for rapid sea ice
decline in the Arctic
1
1
1
Alexander Slavin , Bruno Tremblay , David Straub
1
Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Canada
There exist strong Ekman pumping velocities beneath active leads in the sea ice cover where
discontinuity in the sea-ice velocity and the ice-ocean momentum transfer is present. Here, we
consider whether this can lead to significant advective fluxes ventilating heat from the warm Atlantic
layer and influence the sea-ice mass balance. More general - can reduce ice growth or increase ice
melt. To this end, we use a high-resolution (4.5 km) coupled ocean-ice general circulation model
(MITgcm) forced with contemporaneous atmospheric forcing. One of the motivations of the work was
that fact that as the sea-ice thin during Climate change and it becomes much more mobile. More
mobile ice pack means more active leads and potential of presented mechanism to up-rate much more
strongly.
Using MITgcm we see fewer leads in the Arctic, but we studied those leads closely and scale results
back to real system of RGPS satellite data by knowing how much shear rate we have and knowing
how much ocean heat flux comes beneath those leads. Discontinuities in ice-ocean stress across seaice shears can lead to significant vertical ocean heat fluxes up to 2 orders of magnitude larger than
over stable sea ice. Anomalous upwelling velocities of up to 0.005 cm/sec extending through the Cold
Halocline Layer and into the Atlantic layer. This allows us quantify total potential effect of this Atlantic
water through leads mechanism of heat upweling. We got estimated 8 W/m² vertical heat flux from the
ocean which is equivalent to 40 cm sea-ice melt during a year. This explains observed sea ice decline
trend of last decade and gives us different view of the Arctic. After looking at places with active leads
we see now that ocean have much more important role in the sea-ice mass balance.
Page | 422
343
The energy budget of melting first-year sea ice in the high Arctic
1
1
1
1
Stephen Hudson , Achim Randelhoff , Angelika Renner , Arild Sundfjord , Mats Granskog
1
Norwegian Polar Institute, Tromsø, Norway
1
The Arctic Ocean, once the domain of thick multiyear ice, is now largely covered by younger sea ice,
much of it seasonal first-year ice. This transition affects many of the processes acting on the Arctic ice
since first-year ice is thinner than and has many physical differences from multiyear ice. To gain a
better understanding of the energy budget of first-year sea ice in the high Arctic in summer, something
not widely studied in the past, we observed the radiative and turbulent fluxes of energy both above
and below an ice floe. The floe, with average thickness around 80 cm, was typical for the region
(82.25° N, 21° E) during the observation period, 26 July to 3 August. Turbulent heat fluxes at the
atmosphere-ice and ice-ocean boundaries were observed at fixed locations. All components of the
radiation budget were monitored continuously at one site. In addition, extensive surveys were carried
out along representative transects to quantify spatial variability of albedo and transmittance.
Combining spatial data and a classified aerial photograph of the floe, we were able to determine the
floe-scale albedo and transmittance and combine this with the other fluxes to get an overview of the
2
larger-scale energy budget. The study area of approximately 0.4 km was 71.5% white ice, 15.5% dark
pond, 7% light pond and 6% open water and had an overall albedo of 0.45 and transmittance of 0.21
under the prevailing cloudy sky. Ponds reduced the albedo of the ice (excluding open water) from 0.55
-2
-2
to 0.47. Absorbed shortwave radiation (10-30 W m at midnight, 80-150 W m at noon) was generally
-2
the largest source of energy to the ice, though oceanic heat fluxes to the ice (−10 to +70 W m ) were
similar to, and in one case much larger than, nighttime solar heating.
Page | 423
1103
Abrupt climate changes and emerging ice-ocean processes in the Pacific
Arctic Region
1
Jia Wang
1
NOAA Great Lakes Environmental Research Lab, Ann Arbor, United States
The purpose of this study is to reveal several emerging physical ice-ocean processes associated with
the unprecedented sea ice retreat in the Pacific Arctic region (PAR). These processes are closely
interconnected under the scenario of diminishing sea ice, resulting in many detectable changes from
physical environment to ecosystems. Some of these changes are unprecedented and have drawn the
attention of both scientific and societal communities. More importantly, some mechanisms responsible
for the diminishing sea ice cannot be explained by the leading Arctic Oscillation (AO), which has been
used to interpret most of the changes in the Arctic for the last several decades. The new challenging
questions are: (1) What is the major forcing? (2) Is the AO, the DA, or their combination, contributing
to the sea ice minima in recent years? (3) How do we use models to investigate the recent changes in
the PAR. (4) Is the heat transport through the Bering Strait associated with the DA? (5) What
processes accelerate sea ice melting in the PAR?
Page | 424
755
Trends in Arctic sea ice and the role of atmospheric circulation
1
2
Masayo Ogi , Ignatius G. Rigor
1
2
Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan, Polar Science Center,
Applied Physics Laboratory, University of Washington, Seattle, United States
Recently, Arctic sea ice has dramatically declined in all months, reaching record low levels in
September 2007 for the period 1979-2010. The September sea ice extent has retreated following a
maximum in 1996, and record lows were in 2007, 2008, and 2010. The decrease in the September
sea-ice extent over the Arctic has been accelerating since 1996. The change in the decreasing trend
of summer sea ice extent around 1996 may be correlated with Arctic climate change.
This study examined the contributions of atmospheric circulation anomalies and trends in winter and
summer to changes in Arctic sea ice during the periods 1979-1996 and 1996-2010. In particular, we
found that summer 925-hPa wind and sea ice concentration over the Arctic had opposite sign before
and after 1996.
During the earlier period, the 925-hPa winds over the Arctic tended to be cyclonic and summer SIC
increased north of Alaska and Siberian. In the recent period, summer anticyclonic wind forcing over
the Arctic toward Fram Strait contributed to the decrease in summer SIC over Siberian and north of
Alaska. The recent strong anticyclonic circulation has caused an accelerating decrease in the Arctic
sea ice in summer.
Page | 425
A5.4a - Asian glaciers and climate change
10.07.2013 08:15-09:45, Aspen II
663
Snow and ice variations in the Central Asian mountains recovered by GRACE
1
1
1
1
1
Daniel Farinotti , Andreas Güntner , Franz Barthelmes , Doris Düthmann , Abror Gafurov , Matthias
1
1
1
Huss , David Kriegel , Sergiy Vorogushyn
1
GFZ German Research Centre for Geosciences, Potsdam, Germany
Since its launch in 2002, the Gravity Recovery and Climate Experiment (GRACE) has revolutionized
the way large mass changes can be detected on Earth. In this contribution, time-variable gravity data
available for the period 2002-2011 from the GRACE mission are used for detecting and analysing
mass variations in both the seasonal snow cover and the glacier systems of the Pamir and Tien Shan
mountain ranges, Central Asia. The contribution of snow and ice to the total mass changes are
recovered from the gravity data by subtracting the signals of the surface- and groundwater storage by
means of a suite of different global hydrological models. The use of different models, combined with a
series of different GRACE solutions and filtering approaches, allows estimating a bandwidth for the
accuracy of the results. Validation is performed by independent observations such as seasonal snow
extents from remote sensing, local precipitation measurements, and sparse information about glacier
mass balance. The residual signal shows marked seasonal variations and a slight negative trend over
the considered time period.
Page | 426
1212
Monitoring of glacial retreat and mass balance in Baspa basin, India using
remote sensing technique
1
1
2
3
4
Vinay Kumar Gaddam , Anil V Kulkarni , Markus Stoffel , Nadine Salzmann , Mario Rohrer
1
2
Divecha Centre for Climate Change Indian Institute of Science, Bangalore, India, Climatic Change
and Climate Impacts, Institute for Environmental Sciences, University of Geneva, Carouge-Geneva,
3
4
Switzerland, Department of Geosciences, University of Fribourg, Fribourg, Switzerland, Meteodat
GmbH, Zurich, Switzerland
Snow bound Himalayan regions play an important role in the water resource management of various
basins of North Indian states. But this source of water depends on the distribution of glaciers and on
changes in glacier mass balance. This study is based of Equilibrium Line Altitudes (ELA), which allows
mass balance estimations of a large number of glaciers. The glacial retreat and mass balance
changes for 19 glaciers were estimated. In an earlier study, the glacier area was obtained for the year
2
1962 using Survey of India topographic maps, yielding a measured surface of 173 km . In this study,
2
the areal extent for the same glaciers was estimated to 145.2 ± 10.1 and 131.9 ± 8.37km ,
respectively, for the years 1998 and 2009.
ELA was calculated using hypsography derived from ASTER DEM and a polynomial fit. The mean
ELA was estimated for five years between 1998 and 2011. The maximum altitude of snow line is
varying between 5146 ± 178 and 5320 ± 172m. Then mass balance was calculated using
Accumulation Area Ratio (AAR) method. The negative mass balance was estimated for all five years.
The temperature data of Raksham located in the basin at an altitude 3500 m and precipitation data of
Kaza in the adjacent basin at an altitude of 3600 m were analyzed. The increasing trend in annual
temperature and decreasing trend in annual precipitation was observed for a period between 1984
and 2009.
Page | 427
62
Decadal seasonal snow cover changes in Sikkim Himalaya
1
1
Smriti Basnett , Anil V. Kulkarni
1
Divecha Centre for Climate Change, Indian Institute of Science, Bangalore, India
In this study, snow cover in Sikkim has been monitored using : (a) 200 imageries of Advanced Wide
Field Sensor (AWiFS) of Indian Remote Sensing Satellite for 2004-2008, and (b) 448 snow products (8
composite) from Moderate Resolution Imaging Spectroradiometer (MODIS), for 10 years from 2002 to
2011. To generate snow cover statistics for Sikkim, algorithm based on Normalised Difference Snow
Index (NDSI) was used on AWiFS, and MODIS Snow tool Version 1.0.0, developed by ICIMOD and
was applied on MODIS snow products. The uncertainties in snow cover estimates was obtained by
using AWiFs data. Average snow cover area (SCA) estimated for the period 2002-2011 was 2388 ±
2
43.58 km , about 33.57 ± 1.83 % of the total land area. The maximum snow extent of 53.64 ± 6.93 %
was observed in February, indicating influence of Western Disturbances. Interannual and seasonal
SCA both showed a decline. The mean annual SCA in Sikkim showed a decrease of 2.98 ± 1.83 % for
a decade between 2002 and 2011, with two times higher SCA decrease (-6.43 ± 4.48 % ) in the
summer season but the monsoon and autumn showed high variability in the SCA. The temperature
data of Gangtok meteorological station (1812 m a.s.l.) between 2002 and 2011 was analysed. The
temperature analyses showed that the region experienced a 0.76°C rise in the summer temperature
and a 2.19°C rise in the winter temperature for a period between 2002 and 2011. These studies,
indicate that snow cover in Sikkim is changing, and the rise in temperature has potential to affect
seasonal variability and influence the runoff in the Tista River.
Page | 428
260
Identification of potentially dangerous glacial lakes in Himachal Pradesh using
remote sensing and GIS techniques
1
1
Chander Prakash , Rajeshwar S. Banshtu
1
Civil Engineering, National Institute of Technology, Hamirpur, India
Mountain glaciers interact sensitively with climate and therefore they are considered as climate
indicators. The climate change of the 20th century has had a pronounced effect on glacier
environments of the Himalayas. Warmer climates of the past 100 to 150 years have resulted in
widespread glacial retreat and the formation of glacial lakes in many mountain ranges.The formation of
moraine dammed glacial lakes at the snout of the glacier and outburst floods from such lakes are a
major concern in countries such as Bhutan, Tibet (China), India, Nepal and Pakistan. These glacial
lake outburst floods (GLOF,) can cause extremely high water discharges as well as large mudflow
events. Triggering events for an outburst can be moraine failures induced by an earthquake, by the
degradation of permafrost and increased water pressure, or falling of a rock, snow, or ice avalanche
into the lake causing a flood wave with a subsequent outburst. The instantaneous discharge of water
from such lakes can cause flash floods, enough to create enormous damage in the downstream areas.
The hazardous lakes, however, are situated in remote areas and are very difficult to monitor through
ground surveys due to the rugged terrain and extreme climatic conditions. Therefore, remote sensing
data and GIS are ideal tools for studying and monitoring glacial lakes and assessing their hazard
potential. GIS is capable of integrating and aggregating the data acquired from different sources i.e.
topographic maps, satellite data, published reports etc. Glacial lakes are identified and mapped from
the satellite data using image processing tools. The glacial lakes and surrounding characteristics such
as slope, geology, geomorphology, etc are used to identify the potentially dangerous glacial lakes.
Page | 429
58
Annual mass balance and accumulation status of glaciers in Lahaul-Spiti,
Himachal Pradesh
1
1
1
1
1
Ramanathan Alagappan , Anurag Linda , Pottakkal G. Jose , Virendra Singh , Parmanand Sharma ,
2
3
1
Mohd. F. Azam , Patrick Wagnon , Thupstan Angchuk
1
2
School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, India, LGGE UMR
3
5183, LTHE UMR 5564, IRD/UJF - Grenoble I/CNRS/G-INP, Grenoble, France, I/CNRS/G-INP,
LGGE UMR 5183, LTHE UMR 5564, IRD/UJF – Grenoble I/CNRS/G-INP, Grenoble, France
This study has been carried out in Chotta Shigri and Patsio glaciers,Lahaul-Spiti district, Himachal
Pradesh. Mass balance studies were carried out in Chotta shigri from 2002 and winter/spring balance
has also been initiated from 2009 onward to understand the variation in accumulation pattern of this
glacier with respect to annual mass balance. In Patsio annual mass balance monitoring was initiated
from 2010-11. Depth wise snow data were collected from the glacier surface at different altitudes
during winter. Density of snow was calculated by their Stratigraphy. Specific winter balance of the
Chotta Shigri in year 2008-09, 2009-10 and 2010-11and 2011-12 are very positive to slightly negative
. In 2011-12, overall specific annual mass balances in both the glaciers shows same trend. Since
2009-11. Chotta shigri glacier has shown positive mass balance that is reflected in the winter balance
as well. There is direct relation between specific winter balance and specific annual mass balance and
their interrelationship can be confirmed only through long term monitoring of winter accumulation.
Maximum accumulation was found in 2009-10, with an average of about three meters of snow
accumulation. Mean vertical gradient of accumulation varied with altitude. Between 2003 and 2010,
elevation and ice-flow velocities slowly decreased in the ablation area, leading to a considerable
reduction in ice fluxes showing their response of the glacier dynamics to its mass balances changes
The reduced ice fluxes are still far larger than the balance fluxes calculated from the 2002-10 average
surface mass balances. Limited surface velocity changes observed between 1987-89 and 2003/04
along with a smaller terminus changes between 1988 and 2010, suggesting that the glacier has
experienced a period of slightly positive mass balance in the 1990s, before shifting to a strong
st
imbalance in the early 21 century.
Page | 430
A6.2c - Ice sheet – ocean – atmosphere interactions
10.07.2013 08:15-09:45, Forum
825
Response of the Greenland ice sheet in a 4xCO2 climate scenario
1
1
1
1
Synne H. Svendsen , Marianne S. Madsen , Shuting Yang , Christian Rodehacke , Gudfinna
2
Adalgeirsdottir
1
2
Danish Meteorological Institute, Copenhagen, Denmark, University of Iceland, Reykjavik, Iceland
Coupling an ice sheet model to an atmosphere-ocean model makes it possible to study the response
of the Greenland ice sheet to global climate change taking system feedbacks into account.
In this study, the ice sheet model PISM (Parallel Ice Sheet Model) has been coupled to the Earth
System model EC-Earth in a two-way coupling scheme and a 4xCO2 scenario run has been performed
in order to study the response of the Greenland ice sheet to global climate change.
Monthly fields of surface mass balance and temperature from the climate model EC-Earth are used to
drive the Greenland ice sheet model PISM for one year and the resulting changes in ice sheet
topography and freshwater input to the ocean are given back to EC-Earth once a year, thereby
obtaining a two-way coupling between PISM and EC-Earth. A simulation with CO2 concentrations
reaching 4 times the preindustrial level is performed, starting with a 1% annual increase in CO2 until 4
times the preindustrial CO2-concentration is reached followed by stabilisation at this level.
The characteristics of the Greenland ice sheet in a 4xCO2 climate are examined and compared to
present-day conditions. The present day Greenland ice sheet is defined as the outcome of a 100.000
year spin-up run forcing the ice sheet with the constant pre-industrial mean climate of EC-Earth. Ice
sheet geometry, discharge and flow velocities are examined for each of the two ice sheet states and
key points in their mutual differences are identified.
Page | 431
968
Antarctic surface mass balance simulated with a regional climate coupled with
a blowing snow model and a snow pack model
1
Hubert Gallée
1
Laboratoire de Glaciologie et Géophysique de l'Environnement, Saint-Martin d'hères, France
The regional climate model MAR has been used to simulate transport of snow by the wind in Adélie
2
Land, Antarctica, over a small domain (500 x 500 km ) and with a fine horizontal resolution (5 km).
Simulation of January 2010 is performed and the agreement with the observation is excellent, as it is
inferred from statistical tests. Even if slightly underestimates detection of snow transport events, the
set-up of the model over the whole antarctic ice sheet with an horizontal resolution of 40 km exhibits a
contribution of the transport to the surface mass balance which is larger than previously estimated.
Page | 432
406
Effects of snow grain size and snow impurity concentrations on albedo
variation at SIGMA-A on Greenland ice sheet
1
2
3
4
1
Teruo Aoki , Sumito Matoba , Satoru Yamaguchi , Tomonori Tanikawa , Masashi Niwano , Tetsuhide
5
1
6
4
Yamasaki , Katsuyuki Kuchiki , Hideaki Motoyama , Masahiro Hori
1
2
Meteorological Research Institute, Tsukuba, Japan, Institute of Low Temperature Science, Hokkaido
3
University, Sapporo, Japan, National Research Institute for Earth Science and Disaster Prevention,
4
Nagaoka, Japan, Earth Observation Research Center, Japan Aerospace Exploration Agency,
5
6
Tsukuba, Japan, Arctic Explorer, Osaka, Japan, National Institute of Polar Research, Tachikawa,
Japan
To clarify the contributions of light absorbing snow impurities to recent abrupt melting of snow/ice in
Greenland, intensive observations of meteorological and snow parameters have carried out at the site
SIGMA-A (78°03'N, 67°38'W, 1,490 m a.s.l.) on northwestern Greenland ice sheet during the intensive
observation period (IOP) from June 26 to July 16, 2012. We installed automatic weather station to
measure the meteorological elements, radiation budget, snow temperatures, and relative snow height.
We have also performed snow pit work and snow samplings for light absorbing snow impurities.
During the IOP no precipitation was observed in the first two weeks and a large amount of rainfall with
remarkable lowering of snow surface was observed in the middle of July, when a melting event of
surface snow/ice over 97% of Greenland ice sheet occurred. Snow grain shapes observed from snow
pit work for snow layer of about 80 cm (annual accumulation) changed from melt forms for upper layer
and depth hoar beneath that to melt forms for all layers during the IOP. Light absorbing snow
impurities found from snow samples were black carbon (BC) and mineral dust, whose concentrations
at surface were both increased from 0.9 ppbw to 4.9 ppbw and from 102 ppbw to 1327 ppbw during
the IOP, respectively. We calculated the possible albedo reduction by the measured snow impurity
concentrations using a physically based snow albedo model. The maximum albedo reduction due
even to EC of 4.9 ppbw is less than 0.01 for typical grain size of melt forms, while it could be
enhanced by the effect of dust of 1327 ppbw. BC equivalent total impurity concentration is estimated
to be about 15 ppbw (albedo reduction -0.015). This result was consitent with the albedos measured
during IOP.
Page | 433
1039
Trends in coastal Arctic fog and its influence on the surface energy balance of
glaciers
1
2
2
Hester Jiskoot , Soukeyna Y. Gueye , John H. van Boxel
1
2
Department of Geography, University of Lethbridge, Lethbridge, Canada, Institute for Biodiversity
and Ecosystem Dynamics (IBED), University of Amsterdam, Amsterdam, Netherlands
Breakup of sea ice causes advection and steam fog, which can be persistent over oceans and coasts
but diminishes inland. Arctic warming has increased summer sea ice decline and open water
exposure, affecting heat and moisture fluxes and therefore cloud formation. Cloudiness has generally
increased over the Arctic, but trends differ with cloud vertical distribution as well as seasonally and
spatially, with disparate patterns over broken sea ice, open ocean and land. The few studies that
separate fog from other clouds report a slight increase in sea fog and slight decrease in land fog over
the past decades, but regional and pan-Arctic patterns are equivocal. No studies have focussed on the
coast-to-inland transition zone, where many ice sheet outlets and glaciers terminate and where it is
suggested that fog and related temperature inversions suppress glacier melt.
In this study, we investigate whether melt season fog frequency and timing has changed in coastal
regions around the Greenland Sea over the past 50-70 years. Fog occurrence and characteristics
were analysed using synoptic weather data from East Greenland, Jan Mayen, Svalbard and Iceland
national and research stations, supplemented with Integrated Global Radiosonde Archive and
International Arctic Buoy Programme data. A multivariate fog detection model was developed on the
basis weather stations with direct (visibility) and indirect (temperature, relative humidity, wind) fog
data. This fog detection model was then applied to stations without direct fog observations, after which
daily to seasonal trends in peak frequencies, total fog occurrence, and spatiotemporal patterns could
be analysed for the Greenland Sea coastal regions. Occurrence of Arctic sea fog coincides with the
glacier ablation season and peaks in July/August. Using fog layer height and atmospheric properties
from radiosonde data we calculated fog inland extent onto glaciers and its possible effects on the
surface radiation budget.
Page | 434
C2.1/C2.3 - Dynamics and impact of ice formation in clouds / Clouds, aerosols
and precipitation at high latitudes
10.07.2013 08:15-09:45, Studio
736
A modeling study of the aerosol effects on mixed phase convective clouds with
a new cloud droplet activation scheme
1
1
Seong Soo Yum , Hannah Lee
1
Yonsei University, Seoul, Korea, Republic of
Aerosol effects on cloud and precipitation development have been recognized as a fundamental issue
in climate change in recent decades. Due to the modulation of the cloud microphysical properties by
anthropogenically introduced aerosols, clouds can become brighter and last longer. These aerosol
indirect effects can contribute to the cooling of the earth atmosphere but a qualitative estimate of these
effects is notoriously uncertain. Even more uncertain is the aerosol effects on precipitation, especially
in mixed phase clouds that contain ice hydrometeors. There have been many studies on this subject in
recent years, mostly using a cloud resolving model with bin microphysics. In these studies aerosols
were assumed to be of one chemical composition and/or the newly formed droplets by a cloud droplet
activation scheme could be too large for newly formed droplets. Here we propose a new cloud droplet
activation scheme that can take into account the aerosol hygroscopicity, a crucial factor that
determines the aerosols' capability to activate as a cloud droplet at a given supersaturation and also
can limit the newly formed droplets to be of realistic sizes. We applied this new cloud droplet activation
scheme to a cloud model with bin microphysics and studied the aerosol effects on mixed phase
convective clouds. The three aerosol distributions, maritime, continental and polluted, classified
according to aerosol concentration, were used as the input aerosol distribution. To be consistent with
several other studies, the polluted cloud produced greater precipitation amount. Precipitation started
faster in the maritime cloud but in the later stage graupel growth became much more efficient mainly
due to the riming of much higher concentration of supercooled droplets and thus precipitation became
much more intense in the polluted cloud. The aerosol invigoration effect was not clearly visible at least
in terms of the vertical extent of clouds.
Page | 435
1210
The simulation study of the interaction between aerosols and clouds in heavy
air pollution weather in East China
1,2
Hong Wang
1
2
Chinese Academy of Meteorological Sciences (CAMS), Beijing, China, Insititute of Atmospheric
Composition, Beijing, China
The aerosol-radiation interaction is coupled into an online mesoscale weather and aerosol forecasting
model GRAPES_CUACE which focuses on severe air polluting weather episodes prediction in East
Asia. The aerosols direct radiative feedbacks on heavy air pollution weather are simulated and
studied. Aerosols optical depths, single scattering albedo, asymmetry factor, instant radiative forcing,
radiative heating/cooling rates on the air, together with the changes of air temperature, pressure,
turbulent diffusion, geopotential height, the high and surface circulation pattern driven the severe air
pollution episode. The changes of local and regional circulation pattern finally have evident impacts on
the clouds, which is simulated and analyzed in this paper. The results shows aerosols direct radiative
effects may cool the surface and lower atmosphere over which contributes to the atmosphere status
with the cold air in lower atmosphere and warm air in upper atmosphere. The turbulent diffusion
coefficient is reduced which suggests the weakening of local turbulent diffusion process of atmosphere
by aerosol direct radiative feedbacks. The low-pressure system in the surface, which leads to
developing and keeping of the local heavy pollution episode in East Asia, is also deepened by
aerosols radiation. These results suggests that aerosols direct radiative feedback is benefits to keep
the mesoscale stable condition of the local atmosphere which further impacts on the local and regional
clouds in East Asia.
Page | 436
283
The role of different modes of ice initiation for rain formation
1
1
1
Thibault Hiron , Marie Monier , Flossmann Andrea
1
LaMP, University Blaise Pascal/CNRS, Aubière, France
In mid-latitudes most clouds develop rain while passing through the ice phase. In order to initiate the
ice phase at temperatures above -35°C, particular aerosol particles are necessary, called IN (ice
nuclei). Only little is known regarding the requested properties of an aerosol particle to act as IN at a
certain temperature region. Furthermore, it is uncertain whether they will act through condensation
freezing, immersion freezing or contact freezing. Even though recently some additional data have
become available, the initiation of the ice phase and its role for precipitation formation remains
unclear.
In order to explore the importance of ice nucleation pathways for rain formation the detailed binresolved microphysics model DESCAM is used. It is the only model currently available which follows
explicitly the size of liquid and solid hydrometeors, the aerosol particle population on which they form
and the pollution mass inside all hydrometeors. Recently, it has been extended to follow in a rigorous
way the different ice nucleation modes from an ambient or activated aerosol particle population. Also,
it includes now two different types of aerosol particles and allows to study explicitly e.g. the role of
giant CCN and IN, like volcanic ashes or bacteria in a given background pollution environment, on
cloud evolution.
This model has been used to study the role of the different modes of ice initiation on rain formation
using data from the literature, coupled with to sensitivity tests.
Page | 437
B3.1d - General dynamics
10.07.2013 08:15-09:45, Wisshorn
265
Dynamics and the quasi-geostrophic ω-equation
1
Huw Davies
1
Institute for Atmospheric and Climate Science, ETH, Zurich, Switzerland
Consideration is given to the dynamics and the basic kinematics associated with the quasi-geostrophic
ω-equation. Attention is focussed on the formulation(s) of this equation's so-called 'Forcing Function'
that have been proposed to enable the qualitative inference and the dynamical interpretation of the
synoptic-scale regions of ascent from direct inspection of synoptic charts. A critique of four extant
formulations of the 'Forcing Function' (viz. the traditional, the Sutcliffe-Fjortoft, the Q-vector, and the
PV forms) serves to pinpoint their various shortcomings, and to prompt the derivation of some (yet
more!) alternative forms.
Attention is also drawn to the utility and value of the quasi-geostrophic ω-equation given that
nowadays the vertical velocity is available as a model output field and the finer meso-scale patterns of
the flow captured in NWP models are assumed to be beyond the restrictions of quasi-geostrophy. Coexamination of model-based Q-vectors and vertical motion patterns reveal a surprising degree of
agreement as well as distinctive and major disagreements. The associated dynamics is shown to be
subtle and integral to the nature of:- balanced flow, the development of intricate patterns of nearsurface baroclinicity; and the character of baroclinic development.
Finally it is argued that a deployment of a 'balanced flow' Omega Equation is both warranted (- and
arguably necessary) when considering the NWP issues of model resolution, stochastic representation
of near-grid scale processes, and the assimilation of meso-scale cloud-diabatic effects.
Page | 438
209
Quantifying contributions to Rossby wave train propagation
1
1
Franziska Gierth , Michael Riemer
1
Institute for Physics of the Atmosphere, Johannes Gutenberg-University, Mainz, Germany
Rossby wave trains are a fundamental ingredient of the synoptic- to large-scale dynamics of the
midlatitudes. It is well known that these wave trains are linked to surface cyclones, blocking, and
convective systems and thus play an important role in producing midlatitude weather events. Based on
the classic Eady model, Rossby wave trains can be described as the interaction of upper- and lowertropospheric Rossby waves. Recent work has shown that diabatic processes, in particular latent heat
release associated with cloud formation, may have also a considerable impact on the amplitude and
propagation of these wave trains. A primary goal of this study is to quantify the relative importance of
these processes for real atmospheric Rossby wave trains.
Wave train dynamics is investigated in a potential vorticity (PV) - potential temperature framework.
Piecewise inversion of PV is applied to quantify the contributions to propagation and amplification by
the upper-level wave itself, and by baroclinic feedback of the low-level temperature wave and interior
PV anomalies. The PV inversion is complemented by examination of the divergent flow and by
diabatic tendencies derived from the Year Of Tropical Convection data.
Analysis will be presented of selected Rossby wave train life cycles. As might be expected, baroclinic
and diabatic processes play a prominent role in the amplification of wave trains while the propagation
is dominated by the upper-level Rossby wave itself. Diabatic and baroclinic proceses are, locally and
temporally, of the same importance as upper-level wave propagation. Strong diabatic and baroclinic
contributions tend to be associated with oceanic cyclones, with a large case-to-case variability.
Potential implications for the predictability of Rossby wave trains will be discussed briefly.
Page | 439
284
A Lagrangian PV perspective on diabatic flow modifications in a moist
extratropical cyclone
1
1
Sebastian Schemm , Heini Wernli
1
Institute for Atmospheric and Climate Science, ETH, Zürich, Switzerland
The inherent content of moisture in the atmosphere plays a key role in the amplification of extratropical
cyclogenesis and growth. In this numerical modeling study of an idealized extratropical cyclone, the
role of moisture in the enhancement of the strongest surface winds (low-level jet), the amplified growth
of the downstream cyclone and their dynamical linkage is revealed. We illuminate the differences
between a dry and a moist cyclogenesis from a Lagrangian potential vorticity (PV) perspective. In
particular, we consider the temporal evolution of PV along two coherent air streams, the warm and
cold conveyor belt, both are identified by an objective trajectory selection criteria. In the presence of
latent heat release, PV is diabatically generated typically below the maximum and destroyed above.
The thereby formed PV anomalies are then advected by the cold and warm conveyor belt. Based on
the inversion principle, the changes in the balanced horizontal wind field associated with PV
anomalies, allows us to deduce how latent heat release can alter the strength and circulation of the
flow. By relating the advection of diabatically generated PV anomalies to the conceptual conveyor belt
model, we find a spatio-temporal coherence between the observed amplification of the low-level jet
and the enhanced growth of the secondary cyclone downstream. On the one hand, the warm
conveyor belt advects a negative PV anomaly towards upper levels, where it perturbs the Rossby
wave guide and subsequently enhances the growth of the downstream cyclone. On the the hand, the
cold conveyor belt advects high PV air rearward along the bent-back front, where we find an
intensification of high surface winds. We show how the high PV air, advected by the cold conveyor
belt, is formed below a major maximum of latent heat release, formed by the ascending warm
conveyor belt air.
Page | 440
349
Helicity and potential vorticity in a moist atmosphere
1
Michael Kurgansky
1
A.M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Moscow, Russian
Federation
Applications are considered of the Ertel potential vorticity theorem and the general helicity balance
equation to analysis of adiabatic helical vortex motion of unsaturated and/or saturated moist air - the
latter in the presence of either liquid water or ice in equilibrium with its vapor - and for clarifying the
conditions of spontaneous amplification (generation) of helicity due to the atmospheric baroclinicity
and compositional inhomogeneity. A formulation of the dynamics of these fluids in the form of Nambu
mechanics, which serves a certain generalization of the Hamiltonian mechanics, will be given. Critical
comparison with the case of dry atmosphere will be made. Possible modification of the used
methodology onto the case of moist precipitating atmosphere will shortly be outlined, aiming inter alia
at possible applications to the problem of tornadoes and waterspouts origination.
Page | 441
390
Symmetric instability under full-component Coriolis force
1
Itano Toshihisa
1
Department of Earth & Ocean Sciences, National Defense Academy, Yokosuka, Japan
The theory of symmetric instability has been developed under the so-called “traditional approximation”,
i.e. by neglecting the horizontal component of the planetary vorticity. Despite several trials to include
this component into the theory, no satisfactory results were obtained due to misunderstanding and
miscalculation in the process of handling the governing equations. Here, it is desirable to derive
complete solution of symmetric instability under the full-component of Coriolis force. We have tried to
this problem and extracted some successful results.
In this analysis, symmetric instability can be extended naturally into the case including the horizontal
component of the planetary vorticity. A minimum set of dimensionless numbers governing the
instability is shown to consist of the ratio between frequencies of gravity and inertial waves including
the effects of shears in the basic flow, the slope of the constant momentum surface, and the slope of
the isopycnic surface including the nontraditional Coriolis effects. The dimensionless numbers,
therefore, remain three in spite of the addition of new components associated with the horizontal
component of the planetary vorticity. Meanwhile, the condition of symmetric instability can simply be
generalized as “the slope of the isopycnic surface including the nontraditional Coriolis effects is
steeper than that of the constant momentum surface.”
When boundaries are imposed, for example, at the top or bottom of the domain, the numbers of
modes increase four instead of two in the case of no boundary. Such strange behavior of symmetric
instability, which had first been discovered in the inertio-gravity waves in the case of including the
horizontal component of the planetary vorticity, can be interpreted clearly based on the dynamics of
incident and reflected waves.
Page | 442
D1a - Economics of weather and climate risks
10.07.2013 08:15-09:45, Schwarzhorn
422
Assessment of risk and opportunities related to climate change as contribution
to the Swiss Adaptation Strategy
1
2
2
2
2
3
Michael Bründl , Niels Holthausen , Peter Locher , Lilian Blaser , Sabine Perch-Nielsen , Marco Pütz ,
4
4
4
4
Pamela Köllner-Heck , Martina Zoller , Thomas Probst , Roland Hohmann
1
2
WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland, Ernst Basler +
3
Partner, Zollikon, Switzerland, Swiss Federal Institute for Forest, Snow and Landscape Research
4
WSL, Birmensdorf, Switzerland, Federal Office for the Environment, Bern, Switzerland
In many countries adaptation strategies are being developed in order to cope with the expected
consequences related to climate change but also to judge the opportunities. As a contribution to the
Swiss adaptation strategy, a semi-quantitative assessment of risk and opportunities in several sectors
like e.g. health, agriculture or energy, is conducted on a regional scale. The results from regional case
studies conducted in six cantons are used for upscaling to the whole of Switzerland.
We quantify the effects of climate change to short-term hazards like e. g. heat waves but also to longterm and slow on-set changes, as e.g. the rise of mean air temperature. Where quantification is not
possible, we rely on qualitative information. For each sector we evaluate the annual risks and
opportunities for the situation today (2010) and for 2060 by considering two climate change scenarios
and one socio-economic and demographic scenario. The results are compared across all sectors
depicting the uncertainties and clearly stating all assumptions.
Here, we present the results of the case study “Canton of Aargau”, representing the region “Mittelland”
in Switzerland. Our investigations suggest a relatively large climate-induced increase in human health
risk, and a relatively large increase in opportunities in the energy sector (reduction of heating). The
increase in human health-related risk is mainly due to an increased mortality of elderly people caused
by more frequent and more intense heatwaves, as well as to an increased exposure to allergenic
pollen caused by a longer vegetation period.
The results from all regions will allow for comparing the different sectors and will provide a sound basis
for authorities and stakeholders to decide where to put on priorities in adaptation measures related to
Climate Change in Switzerland.
Page | 443
306
Economics of climate adaptation - a call to manage total climate risk
1
David Bresch
1
Risk Management, Swiss Re, Zurich, Switzerland
Climate Adaptation measures are available to make cities more resilient to the impacts of climate
change. But decision-makers need the facts to identify the most cost effective investments. Climate
adaptation is an urgent priority for the custodians of national and local economies, such as finance
ministers and mayors. Such decision-makers ask: What is the potential climate-related loss to our
economies and societies over the coming decades? How much of that loss can we avert, with what
measures? What investment will be required to fund those measures - and will the benefits of that
investment outweigh the costs? Our Economics of Climate Adaptation (ECA) methodology provides
decision-makers with a fact base to answer these questions in a systematic way. It enables them to
understand the impact of climate change on their economies - and identify actions to minimize that
impact at the lowest cost to society. It therefore allows decision-makers to integrate adaptation with
economic development and sustainable growth. See
http://media.swissre.com/documents/rethinking_shaping_climate_resilent_development_en.pdf
Page | 444
871
Global warming-induced impacts on windstorm losses in the German private
household sector in the context of climate economics
1
2
3
4
3
Hermann Held , Friedrich W. Gerstengarbe , Tobias Pardowitz , Joaquim G. Pinto , Uwe Ulbrich ,
2
4
2
3
4
Uwe Böhm , Kai Born , Matthias Büchner , Markus G. Donat , Melanie Karremann , Gregor C.
5
4
3
2
2
2
Leckebusch , Patrick Ludwig , Katrin Nissen , Thomas Nocke , Hermann Österle , Boris F. Prahl ,
2
6
Peter C. Werner , Olaf Burghoff
1
2
University of Hamburg - Klima Campus, Hamburg, Germany, Potsdam Institute for Climate Impact
3
4
Research, Potsdam, Germany, FU Berlin, Berlin, Germany, University of Cologne, Cologne,
5
6
Germany, University of Birmingham, Birmingham, United Kingdom, GDV, Berlin, Germany
We present an overview of a complementary-approaches impact project dealing with the
consequences of climate change for the natural hazard branch of the insurance industry in Germany.
The project was conducted by four academic institutions together with the German Insurance
Association (GDV). A causal chain is modeled that goes from global warming projections over regional
meteorological impacts to regional economic losses for private buildings, hereby fully covering the
area of Germany. This presentation will focus on winter wind storm related losses.
For the first time, the GDV supplied their collected set of insurance cases, dating back for decades, for
such an impact study. We downscale an ECHAM5 A1B ensemble by a multi-model approach. We
used two types of regional climate models that conceptually differ at maximum: a dynamical model
(CCLM) and a statistical model based on the idea of biased bootstrapping (STARS). As a third option
we pursued a hybrid approach (statistical-dynamical downscaling). For the assessment of climate
change impacts, the buildings' infrastructure and their economic value is kept at current values.
For all three approaches, a significant increase of average storm losses and extreme event return
levels in the German private building sector is found for future decades assuming an A1B-scenario.
Compared to 1971-2000, we find a maximum increase of return values of up to 58% for 2071-2100,
across return periods as of 10, 25, 50, and 100 years. We discuss ways to estimate the uncertainty of
our findings as completely as possible. Finally we embed these numbers in the overall climate
economic discourse.
Page | 445
C5.2a - Changing snow and ice hydrology in mountain watersheds
10.07.2013 08:15-09:45, Seehorn
1060
Monitoring the snowpack in remote, ungauged mountains
1,2
Jeff Dozier
1
2
University of California, Santa Barbara, Santa Barbara, United States, Microsoft Research,
Redmond, United States
Our objective is to estimate seasonal snow volumes, relative to historical trends and extremes, in
snow-dominated mountains that have austere infrastructure, sparse gauging, challenges of
accessibility, and emerging or enduring insecurity related to water resources. The world´s mountains
accumulate substantial snow and, in some areas, produce the bulk of the runoff. In ranges like
Afghanistan´s Hindu Kush, availability of water resources affects US policy, martial and humanitarian
operations, and national security. The rugged terrain makes surface measurements difficult and also
affects the analysis of remotely sensed data. To judge feasibility, consider two regions, a validation
case and a case representing the characteristics outlined above. For the validation case, we use the
Sierra Nevada of California, a mountain range of extensive historical study, emerging scientific
innovation, and conflicting priorities in managing water for agriculture, urban areas, hydropower,
recreation, habitat, and flood control. For the austere regional focus, we the Hindu Kush, where some
of the most persistent drought in the world causes food insecurity and combines with political
instability, and occasional flooding. Our approach uses a mix of satellite data and spare modeling to
present information essential for planning and decision making, ranging from optimization of proposed
infrastructure projects to assessment of water resources stored as snow for seasonal forecasts. We
combine optical imagery (MODIS on Terra/Aqua), passive microwave data (SSM/I), retrospective
reconstruction with energy balance calculations, and gridded feed-forward, uncoupled land surface
modeling to establish retrospective context. Specifically, we examine spanning the decade-long record
from Terra and Aqua to bracket the historical record. In the California Sierra Nevada, surface
measurements have sufficient spatial and temporal resolution for us to validate our approach, whereas
in the Hindu Kush surface data are sparse and where access presents significant difficulties.
Page | 446
1276
Radiative forcing by light absorbing impurities in snow: partitioning impacts
from mineral dust and black carbon
1,2
1,2
Sara McKenzie Skiles , Thomas H. Painter
1
Joint Institute for Regional Earth System Science and Engineering (JIFRESSE), UCLA, Los Angeles,
2
CA, United States, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA,
United States
Melt of annual mountain snow cover dominates water resources in the western United States. Recent
studies in the Upper Colorado River Basin have shown that radiative forcing by light absorbing
impurities (LAIs) in mountain snow cover has accelerated snowmelt, impacted runoff timing and
magnitude, and reduced annual flow. However, those studies have assumed that these LAIs are
primarily mineral dust and have not considered the contribution of carbonaceous particles from
industrial and urban sources. Here we quantify both dust and black carbon content and assess their
relative contributions to radiative forcing in snow using a suite of advanced field, lab, and modeling
techniques.
Daily measurements of surface spectral albedo and optical grain radius were collected with a field
spectrometer over the 2013 spring melt season in the San Juan Mountains, CO, Southwestern US.
Coincident snow samples were collected and processed for; (1) dust and black carbon content (2)
impurity particle size, and (3) impurity optical properties. Measured snow/impurity properties were then
used to drive the Snow, Ice, and Aerosol Radiation (SNICAR) model. Unique model runs for clean
snow, only dust, and only black carbon allow us to partition the radiative contribution from each
constituent. This combination of measurements, collected for the first time coincidentally and at such
high temporal resolution, and modeling allows us to better resolve the physical relationship between
impurities, snow properties, and surface albedo. Understanding these processes at the point scale
facilitates the upscaling of this understanding to constraining LAI radiative forcing retrievals by remote
sensing, and to regional climate and hydrology models- where currently the representation of light
absorbing of impurities is poor, and amplification of biases limits the ability to accurately represent
snow cover.
Page | 447
711
Development of a basin-scale snow measurements network in the American
River Basin of California; data for snow-dominated mountain watersheds
1
2
3
3
4
3
Robert Rice , Danny Marks , Roger C. Bales , Martha Conklin , Stephen Glaser , Patrick Womble
1
2
Sierra Nevada Research Institute/University of California at Merced, Merced, United States, USDA
3
Northwest Watershed Research Center, Boise, United States, Sierra Nevada Research Institute,
4
Merced, United States, University of California at Berkeley, Berkeley, United States
The American River basin in the Sierra Nevada is the site for the deployment of a Wireless Sensor
Network (WSN)that will provide distributed estimates of water balance and a full-basin, wellinstrumented research platform. The instrumentation and associated cyberinfrastructure will also
become a core element of a larger water information system for the Sierra Nevada. The WSN is a set
of sensors integrated into a single instrument to make spatial measurements to capture the landscape
variability, and provide both spatially distributed and representative values of snow cover and the
energy that drives the melt across the American River basin. 18 sites have been selected for a WSN in
the American River basin and deployment began summer 2012. Each local WSN are co-located and
centered at existing snow pillow/snow course/meteorological stations, each with a record of
meteorological forcing data that represent the major landscape units in the basin. The forcing data at
these locations include hourly precipitation, wind speed and direction, temperature, and relative
humidity. Validation data includes snow water equivalent, and in some instances snow depth. Longterm meteorological measurements from Alpha, in the American River basin, will be presented,
demonstrating the state of the current long-term forcing and validation data sets in the Sierra Nevada,
and how the WSN deployment will enhance measurements with the addition of a spatially distributed
network of air and soil temperature, relative humidity, and incoming solar radiation, along with snow
depth and soil moisture for validation. Collected hydrologic data will be used for research and
development of the next generation of hydrologic models, as well as modernizing forecasting and
decision-support systems by enabling robust physically based modeling, while enhancing existing
statistically-based forecasting methods, while improving our understanding of basin-scale snow
dominated mountain hydrology.
Page | 448
1003
Using satellite imagery to improve snowmelt predictions in alpine catchments
1
1
1
Tracy Ewen , David Small , Jan Seibert
1
Department of Geography, University of Zurich, Zurich, Switzerland
In alpine regions, the contribution of snowmelt to discharge during the spring melt, in combination with
rainfall events, can create a critical situation for flood generation. In-situ snowmelt data for these
regions are however limited, making flood forecasting for these critical areas difficult. Remotely sensed
data have the potential to provide valuable temporal and spatial information on snowmelt in these
regions where there can be large seasonal variability in the snowpack and anticipated impacts of
climate change will be pronounced. Several recent studies have shown improved modelling
performance with the incorporation of satellite snow cover information into the calibration of the
hydrological model. We extend this to more directly address snowmelt generation by including
information on snowmelt derived from wet snow maps from a large archive of Envisat ASAR wide
swath imagery available over the Alps for the period 2003-2011, to better constrain runoff generation
for several unmanaged alpine catchments in Switzerland using the conceptual rainfall-runoff model,
HBV. Our set-up employs a multivariate calibration technique by including information on snowmelt
timing, in addition to runoff data, to constrain the model. Preliminary results from three alpine test
catchments, Waegital, Ova dal Fuorn and Verzasca in the Swiss Alps show improved runoff modelling
results during the spring melt using the snowmelt information over using the degree day method. In
general, lower temporal and spatial coverage of satellite images during some years limits useful input
for calibration, however in years where there is good coverage and many images available during the
spring melt, modelled runoff is clearly improved.
Page | 449
993
Methodology for snow cover reconstruction using in-situ observations and
remote sensing data
1
1
2
1
1
Abror Gafurov , Sergiy Vorogushyn , Alexander Merkushkin , Doris Düthmann , Bruno Merz
1
2
Section 5.4: Hydrology, GFZ German Research Centre for Geosciences, Potsdam, Germany, Uzbek
Hydrometeorological Service (Uzhydromet), Tashkent, Uzbekistan
Spatially distributed snow cover information can be well observed from remote sensing with
acceptable accuracy in remote areas such as Central Asian Mountains. However, these data are
available only for recent years or decades after satellite missions with proper snow detection
capabilities were launched. Yet, longer time series of snow cover data are required, particularly in
order to calibrate hydrological models in Central Asia where richer meteorological and hydrological
data are available in the past compared to the present state. In this study, we present a methodology
to reconstruct historical snow coverage using recent available remote sensing data and point
information on snow cover observed in the past at existing meteorological stations. It consists of five
subsequent steps which estimate historical snow cover using among others the relationships between
point observations and spatial snow patterns considering seasonal snow cover characteristics and
elevation controls. The methodology is tested in Zerafshan basin of Central Asia. Obtained results are
cross-validated against high resolution remote sensing data and accuracy of about 90 % was
achieved. The methodology can be used to compensate the data gap on spatial snow cover for past
decades.
Page | 450
B7.1a - Atmosphere Ocean and Cryosphere Interactions - BCI
10.07.2013 08:15-09:45, Sertig
501
Science progress from the BRomine, Ozone, and Mercury EXperiment
(BROMEX)
1
2
3
4
5
Son Nghiem , Paul B. Shepson , William Simpson , Donald K. Perovich , Matthew Sturm , Thomas
5
6
7
8,9
8
Douglas , Ignatius G. Rigor , Pablo Clemente-Colón , John P. Burrows , Andreas Richter ,
10
10
11
11
10
Alexandra Steffen , Ralf Ralf Staebler , Daniel Obrist , Christopher Moore , Jan Bottenheim ,
12
12
12
12
13
Ulrich Platt , Denis Pöhler , Stephan General , Johannes Zielcke , Jose D. Fuentes , Dorothy K.
14
15
16
16
16
16
2
Hall , Lars Kaleschke , John Woods , Carl Hager , Joe Smith , Charles R. Sweet , Kerri Pratt ,
2
3
3
3
3
6
Kyle Custard , Peter Peterson , Steve Walsh , Erin Gleason , Eyal Saiet , Melinda Webster , Ross
17
6
1
Lieb-Lappen , Christopher Linder , Gregory Neumann
1
2
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, United States, Departments
of Chemistry and Earth and Atmospheric Sciences, Purdue University, Lafayette, United States,
3
4
Department of Chemistry, University of Alaska Fairbanks, Fairbanks, United States, U.S. Army Cold
5
Regions Research and Engineering Laboratory, Hanover, United States, U.S. Army Cold Regions
6
Research and Engineering Laboratory, Fairbanks, United States, Polar Science Center, Applied
7
Physics Laboratory, University of Washington, Seattle, United States, National Ice Center, NOAA,
8
Washington, United States, Institute of Environmental Physics, University of Bremen, Bremen,
9
Germany, Biogeochemistry Programme, NERC Centre for Ecology and Hydrology, Wallingtonford,
10
United Kingdom, Science and Technology Branch, Environment Canada, Toronto, Canada,
11
12
Division of Atmospheric Sciences, Desert Research Institute, Reno, United States, Institute for
13
Environmental Physics, University of Heidelberg, Heidelberg, Germany, Department of Meteorology,
14
Penn State, University Park, United States, NASA Goddard Space Flight Center, Greenbelt, United
15
16
States, Institute of Oceanography, University of Hamburg, Hamburg, Germany, U.S. Naval
17
Academy, Annapolis, United States, Dartmouth College, Hanover, United States
Punctuated by a new record low in the springtime extent of Arctic perennial sea ice (PSI) in 2012, the
st
change in PSI continues its precipitous decrease since the beginning of the 21 century within the
th
temporal context of observations since the last half of the 20 century. Our objective is to investigate
implications of the sea ice reduction on tropospheric bromine, ozone, and mercury chemical
processes, transport, and distribution. The key science questions are: Will the Arctic sea ice reduction
continue the declining trend? How is the chemical process for bromine explosion initiated from the
surface with different sea ice classes, frost flowers, and snow cover? How is bromine recycled,
distributed, propagated and terminated? How are bromine and thus ozone (O3) and gaseous
elemental mercury (GEM) and more importantly reactive gas-phase mercury distributed in time and in
space and their relationship to oceanic and atmospheric forcing in the changing Arctic environment? If
the Arctic sea ice reduction trend continues, would bromine explosion and O3 and GEM depletion
increase or decrease? As a key component to address these science issues, we conducted the
BROMEX in March-April 2012 around Barrow, Alaska. The field area extended from inland terrestrial
sites to a large region of the sea ice offshore in the Chukchi and Beaufort Seas, where energetic
dynamics created large leads, fortuitously providing a variety of sea ice and atmospheric conditions for
this investigation. BROMEX was successfully carried out with international participation and
contribution of twenty agencies and institutions from U.S., Canada, Germany, and U.K. BROMEX
involved more than a dozen satellite instruments, three different aircraft for instrument deployments
and data collections, multiple field sites on both sea ice and tundra. We will present initial science
progress and identify new research directions emerging from BROMEX.
Page | 451
1067
A case study of a bromine explosion in the Canadian high Arctic
1
1,2
1
3
4
5
Xiaoyi Zhao , Cristen Adams , Kimberly Strong , Robyn Schofield , Xin Yang , Andreas Richter , Jeff
6
Seabrook
1
2
Department of Physics, University of Toronto, Toronto, Canada, University of Saskatchewan,
3
4
Saskatoon, Canada, School of Earth Science, University of Melbourne, Melbourne, Australia, Centre
5
for Atmospheric Science, University of Cambridge, Cambridge, United Kingdom, Institute of
6
Environmental Physics, University of Bremen, Bremen, Germany, Centre for Research in Earth and
Space Science (CRESS), York University, Toronto, Canada
Around the same time as the discovery of the Antarctic ozone hole in the stratosphere, scientists
became aware of severe ozone depletion events in the polar troposphere. These events have since
been linked to extremely high concentrations of bromine, which are called bromine explosion events
(BEEs). There are a number of open questions related to BEEs, particularly regarding bromine
sources, including first-year sea ice, frost flowers, and fresh snow.
In April 2011, we observed a bromine explosion event in the Canadian High Arctic at the Polar
Environment Atmospheric Research Laboratory (PEARL, 86.4°W, 80.1°N), with measurements made
by a ground-based, UV-visible, triple-grating spectrometer. This instrument, the zenith-sky-viewing
PEARL-GBS (PEARL Ground-Based Spectrometer), was permanently installed at PEARL in August
2006 as part of the refurbishment of the laboratory by the Canadian Network for the Detection of
Atmospheric Change (CANDAC). A sun-tracker was installed directly above the PEARL-GBS in 2008,
enabling Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) and direct-Sun/Moon
observations.
We will describe the MAX-DOAS measurements and this BEE case study. A strong tropospheric BrO
rd
th
plume was observed by the PEARL-GBS from April 3 to 5 , 2011. Surface ozone, measured by
ozonesondes, was depleted during this period. Furthermore, the UMUKCA chemistry-climate model
calculated a surface bromine surge and surface ozone depletion, in good agreement with our
measurements. A three-day back-trajectory model (HYSPLIT) and GOME-2 data confirmed that this
BEE was not a local event, and it was also consistent with an airborne lidar measurement of surface
ozone depletion over Arctic sea ice. Finally, age-of-sea-ice data from the NSIDC and interim
reanalysis meteorological data from the ECMWF were used to investigate the source of bromine for
this event. This BEE appears to have been generated from unstable boundary layer meteorological
conditions, which is unusual for bromine explosion events.
Page | 452
211
Investigating formation and transport of polar BrO plumes and links to high
latitude cyclones
1
1
1
Anne-Marlene Blechschmidt , Andreas Richter , John P. Burrows
1
Institute of Environmental Physics, University of Bremen, Bremen, Germany
Intense plumes of bromine oxide (BrO) are regularly observed at the poles over sea ice during polar
spring. Several studies have shown that these high concentrations of BrO can be associated with wide
spread ozone depletion, during an autocatalytic chemical cycle known as the "bromine explosion".
However, there is considerable uncertainty regarding the substrate from which bromine is initially
released to the gas phase. Moreover, not much is known on the transport of BrO by high latitude
cyclones and on the role which these weather systems play in the formation of bromine explosion
events.
This study aims to improve our knowledge on linkages between high latitude weather systems and
BrO explosion events. First results from combined use of satellite observations, numerical weather
prediction and lagrangian trajectory models are presented.
Page | 453
230
Horizontal and vertical distribution of bromine monoxide in northern Alaska
during BROMEX (spring 2012) derived from airborne imaging-DOAS
measurements
1
1
1
2,3
1,4
Denis Pöhler , Stephan General , Johannes Zielcke , Paul B. Shepson , Holger Sihler , Brian H.
5
1
2
6
6
1
Stirm , Udo Frieß , Kerri A. Pratt , Steve Walsh , William R. Simpson , Ulrich Platt
1
2
Institute of Environmental Physics, University of Heidelberg, Heidelberg, Germany, Department of
3
Chemistry, Purdue University, West Lafayette, United States, Department of Earth, Atmospheric, and
Planetary Sciences & Purdue Climate Change Research Center, Purdue University, West Lafayette,
4
5
United States, Max Planck Institute for Chemistry, Mainz, Germany, Department of Aviation
6
Technology, Purdue University, West Lafayette, United States, Department of Chemistry and
Biochemistry, University of Alaska Fairbanks, Fairbanks, United States
Bromine monoxide (BrO) is a reactive halogen species (RHS) and has been known for quite a while to
have a profound impact on the chemistry of the polar tropospheric boundary layer. Details of the
bromine release and reaction processes are still unclear, especially the role of frost flowers, first-year
sea ice, aerosols, atmospheric stability and snow.
To investigate important details of the bromine release, a novel imaging DOAS instrument for the
ultraviolet wavelength range (300 to 400 nm) was deployed aboard a light twin-engine aircraft (ALAR,
Purdue Univ.) as part of the BRomine, Ozone, and Mercury EXperiment (BROMEX) in Barrow, Alaska,
in spring 2012. This instrument utilizes (1) a scanner system in nadir direction to map trace gas
distributions of the overflown area at high spatial resolution and (2) a forward-looking system, to
observe the vertical trace gas distribution. Both viewing directions are equipped with digital cameras,
enabling the creation of aerial maps and the comparison of spectral data with background features.
We derived horizontal and vertical distribution of bromine monoxide (BrO) and other gases (e.g. NO2)
over a wide variety of sea, ice and land surface conditions (first-year sea ice, frost flowers, open leads,
and arctic tundra).
We observed strong horizontal gradients of BrO within few km and a fast movement of BrO plumes.
Distributions change significantly within few hours. The data show interesting correlations to the
different surfaces. Additionally a clear anti-correlation of BrO and NO2 can be observed. Tropospheric
BrO-distributions derived from satellite observations match within the satellite resolution those seen
with the aircraft. Vertical gradients show a shallow layer of BrO close to the surface. These and other
results from the 11 flights will be presented together with conclusions of the involved chemistry.
Page | 454
182
Sea-ice emissions and sea-salt aerosol recycling of bromine in the polar
marine boundary layer
1
1
2
2
Rafael Pedro Fernandez , Carlos Ordoñez , Douglas Kinnison , Jean-Francois Lamarque , Alfonso
1
Saiz-Lopez
1
Laboratory for Atmospheric and Climate Sciences (CIAC), Institute of Physical Chemistry, CSIC,
2
Madrid, Spain, National Center For Atmospheric Research (NCAR), Boulder, United States
A polar module considering full halogen chemistry and time-varying organic and inorganic halogen
emissions into the polar marine boundary layer has been included in the global CAM-Chem chemistry
climate model. The baseline CAM-Chem halogen setup includes natural sources of very short-lived
(VSL) halocarbons from the oceans; reactive chlorine, bromine and iodine species; related
photochemical, gas-phase and heterogeneous reactions, as well as wet and dry deposition for
relevant species. The polar module considers sea-salt aerosol recycling of BrONO2, BrNO2 and HOBr
and sea-ice emissions of Br2 and BrCl as result of recycling over the deposited snow over sea-ice. The
contribution of blowing snow is also considered by means of an enhancement of the recycling
efficiency over fresh sea-ice regions. The external brominated sources posses a 2-fold dependence on
both solar zenith angle and local sea-ice cover. The time/sea-ice dependent local Br2 flux was scaled
to reproduce observations of reactive bromine species over coastal Antarctica, resulting in an Antarctic
-1
mean sea-ice flux of ~200 Gg Br yr .
Model results have been validated locally against boundary layer measurements of BrO performed at
several Antarctic stations and with total and tropospheric BrO columns as reported from satellite
platforms. Results show a good agreement, reproducing both the BrO seasonality and the springtime
maximum peak. The tropospheric BrO cloud distributions is coincident with the Antarctic sea-ice
covered regions as seen by satellites. Further work will quantify the potential of bromine and iodine
chemistry to influence the oxidation capacity of the polar atmosphere.
Page | 455
C4.3a - Atmospheric boundary layers in complex terrain and over ice, snow
and vegetated surfaces
10.07.2013 08:15-09:45, Sanada I
1000
Velocity and buoyancy oscillations in turbulent slope flows: do they live or do
they die?
1
1
Evgeni Fedorovich , Alan Shapiro
1
School of Meteorology, University of Oklahoma, Norman, United States
Characteristic long-period oscillations of velocity and buoyancy fields in natural and
modeled/simulated slope flows have been extensively reported in the literature. Such oscillations
occur in both anabatic flows (winds) along heated sloping surfaces and katabatic flows (winds) along
cooled surfaces. The reported studies indicated that their frequency is typically equal to the product of
the environmental Brunt-Väisälä frequency and the sine of the slope angle. However, evolution of the
oscillation amplitude in time and, especially, the terminal state of oscillations (whether they persist or
dissipate with time) remain topics of scientific discussion. In observational studies, shortness of
measurement records preclude conclusion regarding the time history of oscillations, while in numerical
model/simulation exercises their evolution is often influenced by spurious numerical effects.
A direct numerical simulation approach was used to reproduce oscillatory turbulent anabatic and
katabatic flows along uniformly sloping terrain with a time-constant surface buoyancy-flux forcing. We
tracked the evolution of the oscillations over considerable time intervals (up to several hundreds of
oscillation periods). The simulated oscillations were analyzed in terms of velocity and buoyancy
integrals as functions of time in conjunction with the time evolution of the surface stress. This stress is
the principal oscillation-damping factor in the simulated flow. Depending on the form of the relation
between the surface stress and the velocity integral, the integrated flow system may behave as an
oscillator of a certain type. Analysis of the simulation data has indicated that in our case the system
behaves as an imperfect (“dirty”) underdamped oscillator: after an initial gradual decay of the
oscillation amplitude, the flow evolves into a regime characterized by intermittent, although persistent,
oscillatory eruptions whose magnitude remains relatively small but essentially non-zero. This behavior
points to the linear relation between velocity integral and the surface stress superimposed with
another, apparently random, secondary forcing.
Page | 456
1008
Katabatic flow and nocturnal turbulence observations over a steep alpine slope
1
2
1,2
1
1
Holly Oldroyd , Eric R. Pardyjak , Marc Calaf , Hendrik Huwald , Marc B. Parlange
1
Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne,
2
Switzerland, Mechanical Engineering, University of Utah, Salt Lake City, United States
Katabatic flows, or downslope drainage flows, are thermally driven winds generated over sloping
terrain when the surface is colder than the adjacent air and synoptic forcing is weak. This near-surface
temperature inversion generates a buoyancy field such that denser, cooler air near the surface tends
to sink down the slope and form the katabatic flow. Often these flows can be exploited for wind energy,
and they are important in predicting pollution transport in mountainous regions and the formation of
large cold air pools in valleys and basins. Mean characteristics of katabatic flows over gentle slopes
are well documented. However, small-scale observations of turbulence inside the katabatic jet are less
common, especially over very steep slopes in highly complex topography. Summertime
measurements over a steep slope (36.5°) in a narrow alpine valley (Val Ferret, Switzerland) were
taken with the aim of better understanding the near-surface turbulent fluxes that govern the local slope
flows. Here, a weak katabatic jet with a height less than 1 m characterizes the mean flow. Highresolution, near-surface temperature measurements suggest a shallow internal boundary layer within
the katabatic layer. Turbulent statistics such as velocity and temperature variances, fluxes of
momentum and heat, turbulence kinetic energy (TKE) and local stability parameters are examined to
better understand the physical mechanisms that generate the observed layering. In addition, the
turbulent heat flux varies significantly over the 6 m measurement layer. Hence, Monin-Obukhov
Similarity Theory may be invalid for steep slopes.
Page | 457
899
Turbulent profile analysis of a real case valley flow LES modelling during the
VOTALP campaign
1
1
1
2
Joris Pianezze , Jean-Martial Cohard , Sandrine Anquetin , Yves Gagne
1
2
LTHE, UMR 5564 (CNRS-Grenoble INP-IRD-UJF), Université de Grenoble, Grenoble, France, LEGI,
Grenoble, France
Complex terrains are a major source of uncertainty in weather forecast or climate modelling. In
particular, atmospheric boundary layer within deep valleys, including slope winds and valley winds
development, are not solved correctly, which have dramatic consequences on forecasts of convection,
pollutant transport, etc... Boundary layer dynamic within steep orography has been studied extensively
within idealized frameworks but remains less analysed for real cases. In these latter cases,
simulations are still difficult to be evaluated because of the lack of observation. Moreover Large Eddy
Simulation (LES) model require large computer resources. It therefore limits their applicability to
complex terrains. Finally it is also difficult to prescribe proper boundary conditions to relate the real
forcing from the ground and/or the larger atmospheric scales. Thanks to the rich database of the
VOTALP campaign designed to study ozone transport in a deep valley wind system (south
Switzerland), Méso-NH was run in a 3D LES mode for the 17 august 1996 situation. The simulated
fields are evaluated with sodar and radiosounding profiles, eddy-correlation, scintillometer
observations. This study presents the methodology developed to initialize the model and to implement
realistic boundary conditions using 5 nested models using 16km to 110m horizontal size mesh. It also
presents the evaluation strategy by the use of local observations, and the analysis of turbulent fields
within the valley. The simulation well reproduces the main features of the valley and slope wind
system. Turbulent kinetic energy fields can be interpreted as regard as 2D previous simulation results.
However average refraction index structure parameter doesn´t fit scintillometer observations which are
still questionable. To conclude, LES simulation of complex real case situations is shown to be a
powerful tool to analyse atmospheric boundary layer processes, when uses in synergy with
observations.
Page | 458
1043
Assessing a new scaling hypothesis for turbulent katabatic flow along a planar
slope
1
1
Alan Shapiro , Evgeni Fedorovich
1
School of Meteorology, University of Oklahoma, Norman, United States
A pioneering achievement in the theory of slope winds was the development by L. Prandtl of a onedimensional model for the laminar flow of a viscous stratified fluid along a uniformly heated or cooled
planar slope. This model is prized for the conceptual insights it provides and for a remarkably simple
exact solution of the equations of motion and thermal energy. However, when the same physical
scenario treated by Prandtl is considered in a more realistic turbulent-flow context, the problem
becomes far more complex. Our presentation is concerned with obtaining scaling laws for flow
variables in turbulent analogues of Prandtl-type katabatic flows. Application of the Pi theorem to the
differential equations (and boundary conditions) governing such flows shows that the scaled flows are
fully characterized by (up to) three non-dimensional parameters: the slope angle, Prandtl number, and
a dimensionless parameter (based on viscosity, buoyancy frequency, and a surface buoyancy or
buoyancy flux) that may be interpreted as a Reynolds number. However, by examining the structure of
the governing differential equations in their boundary-layer form, we are able to go beyond the
predictions of the Pi theorem, and deduce scaling laws for the variables that involve only two nondimensional parameters: the Prandtl number and a modified Reynolds number. According to our
scaling hypothesis, the slope angle is not a governing parameter, but appears only as a factor in the
modified Reynolds number and in the scales for the dependent and independent variables. The
validity of the scaling hypothesis is assessed using data from direct numerical simulations.
Page | 459
1211
Criteria for assessing turbulence scaling relations in complex terrain
1
1
1
1
Ivana Stiperski , Mathias W. Rotach , Florian Baur , Florian Karner , Frierdrich Obleitner
1
Institute of Meteorology and Geophysics, University of Innsbruck, Innsbruck, Austria
1
Complex terrain poses a significant challenge to numerical weather prediction or climate simulations.
This can partly be attributed to inadequate parameterizations of near-surface turbulent exchange
processes that rely heavily on scaling relations originally obtained over flat and homogeneous terrain.
The limited number of studies that deal with this problem do not as yet provide a consensus if and
under which specific conditions the scaling relations from flat terrain apply in truly complex topography.
The question also remains as to the processes responsible for the failure of scaling relations to fit the
complex terrain data.
In this study we test the applicability of flat-terrain scaling relations to the data obtained from several
field sites in complex terrain spanning a broad range of stability regimes. These include: i-Box
(Austria), MAP Riviera project (Switzerland) and Kongsvegen glacier (Svalbard). The analysis is
primarily based on nine months of i-Box data obtained from two slope stations and two months of MAP
Riviera data for valley bottom and slope stations. i-Box (short for Innsbruck Box) is particularly
appropriate for this analysis due to its high-resolution, long-term dataset obtained over diverse
characteristic surfaces in truly complex terrain.
The results show that the data fit the flat-terrain empirical similarity relations - but only if strict quality
criteria are imposed. These criteria include: stationarity, homogeneous footprint, correct choice of
planes to fit the data (cf. planar fit method for the post processing of turbulence data), and adequate
averaging periods. Post-processing and measurement uncertainty assessment is shown to be
instrumental in providing a good fit to the theoretical curves. If these quality criteria are met, no
systematic influence of 'complex terrain' (such as slope angle, exposition etc.) was detected so far on
the basis of the present, quite limited data set.
Page | 460
1105
Determination and characteristics of nonstationarity in the surface layer during
the T-REX experiment
1
2
Zeljko Vecenaj , Stephan de Wekker
1
2
University of Zagreb, Zagreb, Croatia, University of Virginia, Charlottesville, United States
Stationarity of turbulence statistics is a fundamental assumption in the theory of homogeneous
turbulence. A lack of stationarity introduces uncertainty in the applicability of statistical turbulence
theory in surface-layer parameterizations. It is therefore important to determine the degree of
nonstationarity in turbulence time series. Many approaches are developed over the years to determine
nonstationarity but so far, there has been no systematic investigation of the differences and similarities
between the approaches. In this paper, we contrast several approaches often used in investigation of
surface layer turbulence, including a statistical test to determine trends (Bendat and Piersol, 1986), a
determination of the Mahrt's (1998) nonstationarity ratio and a determination of the differences
between 5 - and 30 minute variances (Foken and Wichura, 1996). We apply these approaches to time
series of wind and temperature collected during the Terrain-induced Rotor EXperiment in Owens
Valley during spring 2006. Measurements were made on three 30m towers with 6 levels of ultrasonic
anemometers.
Our results show that the degree of nonstationarity varies considerably with the used approach. We
argue that absence of trend is not a sufficient condition for stationarity in time series of variances
because in many cases such time series still show a behavior indicative of intermittent turbulence,
both for stable and unstable conditions. When the trend test is combined with an additional condition
that the intermittency level is below a critical value, this approach resembles the Foken and Wichura
method. Mahrt´s method mostly corresponds with the trend test. We show examples of the degree of
nonstationarity for individual days and a climatology for the entire duration of the experiment. We also
relate the degree of nonstationarity to stability and flow conditions and discuss implications of our
results for the test of surface layer similarity functions in complex terrain.
Page | 461
B4.1e - Global monsoon system: past, present and future
10.07.2013 08:15-09:45, Aspen I
485
The aerosol-monsoon climate system of Asia
1
William K. M. Lau
1
NASA/Goddard Space Flight Center, Greenbelt, United States
In this paper, using observations and modeling, we investigate the coherent variability of the coupled
aerosol-monsoon climate system in South Asia and East Asia, including natural and anthropogenic
aerosol distribution and types, with respect to rainfall, moisture, winds, land-sea thermal contrasts in
the atmosphere from daily, seasonal, interannual to climate change time scales. Specifically, I will
show examples of how aerosol can impact monsoon convection by modifying cloud nucleation
processes; how heat absorbing aerosols (dust and black carbon) over the Indo-Gangetic Plain may
interact with monsoon dynamics to produce feedback effects on the atmospheric water cycle, leading
to a northward shift and enhancement of monsoon rainnfall to the Himalayan foothills in the early
monsoon, followed by subsequent weakening of the peak monsoon over South Asia. I will discuss
possible mechanisms in wihc aerosols may play a role in the North/Dry-South/Wet decadal scale
rainfall anomaly over East Asia, in the broader context of remote climate forcing. Also discussed are
possible long-term impacts of atmospheric heating by aerosols, and darkening of the snow surface by
aerosol deposition in accelerating the melting of snowpack and glaciers over the Himalayas and the
Tibetan Plateau in the pre-monsoon season, resulting in altered evolution of the Asian monsoon.
Page | 462
540
Impacts of the East Asian summer monsoon on seasonal, interannual, and
decadal variations of aerosols in China
1
1
1
1
Hong Liao , Jianlei Zhu , Li Zhang , Li Jianping
1
Institue of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
Understanding the observed decadal-scale weakening of the East Asian Summer Monsoon (EASM)
has been a challenge to scientists worldwide. Studies in the past decades have demonstrated the
important impacts of aerosol direct and indirect forcing on the weakening of the Asian monsoon.
Concentrations of aerosols are determined by both anthropogenic emissions and meteorological
parameters. Variations in meteorological fields associated with the EASM can influence transport,
deposition, and chemical reactions of aerosols. We apply a global three-dimensional Goddard Earth
Observing System chemical transport model (GEOS-Chem) driven by NASA/GEOS4 assimilated
meteorological data to quantify the impacts of the EASM on seasonal, interannual, and decadal
variations of aerosols over eastern China. Sensitivity studies with no seasonal variations in emissions
indicate that the EASM can reduce aerosol concentration averaged over the domain of (110-120E, 2045N) by 60-70%, as the averaged surface-layer aerosol concentration in July is compared with that in
January. Interannually, simulated aerosol concentrations are found to have strong negative
correlations with the strength of the EASM. Accounting for sulfate, nitrate, ammonium, black carbon,
and organic carbon aerosols, the summer surface-layer PM2.5 concentration averaged over eastern
China can be about 18% higher in the weakest monsoon years than in the strongest monsoon years.
We further quantify based on the EASM index that the decadal-scaling weakening of EASM has an
effect of increasing aerosol concentrations over eastern China by the changes in atmospheric
circulation (the convergence of air pollutants). Results have important implications for understanding
the role of aerosols in monsoon system.
Page | 463
824
Aerosol and monsoon interactions: can we separate aerosol effects from
dynamics and other human-induced changes
1,2
Zhanqing Li
1
ESSIC & Dept of Atmospheric and Oceanic Science, University of Maryland, College Park, United
2
States, GCESS, Beijing Normal University, Beijing, China
Various mechanisms of aerosol effects on our climate system have been proposed under highly
constrained conditions. Broadly speaking, they include the direct radiative effect by altering radiation
budget or radiative heating, and the indirect effects by altering cloud properties or semi-direct
direct/indirect effects by altering both radiation and cloud microphysics. In strong monsoon
regions/seasons, any changes in these variables may affect or be affected by the monsoon circulation
and monsoon climate.
By means of observation and modeling on global scales, as well as regional ones in two monsoon
active areas of China and US, we attempt to identify various mechanisms that may govern the impact
of aerosols on a range of meteorological quantities (cloud, radiation, precipitation, wind/circulation,
etc.) from the background influences of dynamics, greenhouse effect and even urbanization. To this
end, we have analyzed masses of global satellite measurements and long-term (~50 years of routine
meteorological data in China, >10 years of extensive and intensive research observations), with the
aid of global and regional simulations driven observation data. Rich evidences/indicators of different
types of aerosol effects will be presented, including the Twomey or microphysical effect, radiative
effects, aerosol invigoration effect and suppressing effect under different environments, etc. Together,
they seem to help explain some long-term trends of changes in several key meteorological variables
such as temperature, rainfall frequency, wind and storms associated with both summer and winter
monsoon systems.
Page | 464
A4.2f - Sea ice and Ocean-Atmosphere Interactions
10.07.2013 10:15-11:45, Sanada II
1198
East Antarctic sea ice: time for change?
1
1
1
2
Petra Heil , Robert A. Massom , Adam D. Steer , Jan Lieser
1
2
Australian Antarctic Division & ACE CRC, University of Tasmania, Hobart, Australia, ACE CRC,
University of Tasmania, Hobart, Australia
Ship-based observations from seven recent cruises off East Antarctica (90 - 110°E) are used to
describe regional change in the thickness distribution and characteristics of sea ice and snow cover
thickness during austral spring. These observations were collected between 2003 and 2012 and form
part of the Scientific Committee on Antarctic Research Antarctic Sea Ice Processes and Climate
(ASPeCt) data set and are compared to previous observations (1992 - 2007) in the region. The total
ice thickness is derived from observations of level ice thickness and surface topography using a
simple ridge model. The long-term mean (standard deviation) total ice thickness, which includes
deformed ice for the region during austral spring was 0.72 (± 0.80) m, and that of level ice only was
0.53 (± 0.43) m. For the region, the long-term mean ice concentration was 71 % with about 12 % of
the ice area covered by surface ridges. The regional long-term mean snow thickness for level ice was
0.15 m. By comparison for the same region during the most recent decade the mean total ice
thickness was 0.87 m (± 0.92) m, with a mean of 0.45m (± 0.38) m for level ice only. At the same time
the snow cover of level ice increased to 0.20 m. To investigate these changes we review the recent
data in context of regionally increased ice concentration, pol-ward retreat in equatorial ice extent, and
changes in the atmospheric surface circulation. Our preliminary finding suggests that a southward shift
of autumnal and early winter atmospheric storm trajectories and a change in their frequency are
associated with increased sea-ice deformation, which consequently increases the aerial coverage of
ridged ice as well as the total ice thickness. Increased snow thickness over level ice might be
associated with the changes in the atmospheric circulation.
Page | 465
1265
Seasonal and interannual variability of Arctic Sea ice albedo
1
2
Gay Perez , Josefino Comiso
1
Institute of Environmental Science and Meteorology, University of the Philippines, Quezon City,
2
Philippines, Cryospheric Sciences Laboratory, NASA Goddard Space Flight Center, Greenbelt,
United States
One of the most important geophysical parameters that can be observed by satellite sensors in the
Arctic is sea ice albedo. Albedo is a key parameter in ice-albedo feedback that serves to amplify
climate signals in the Arctic region. We study narrow-band and broadband albedo using mainly Aqua
and Terra MODIS data and in part AVHRR data in conjunction with SSM/I and AMSR-E data. Albedo
is affected by many factors including the state of the snow cover from spring through autumn. In
spring, albedo starts changing because of onset of melt that can be detected by passive microwave
data because of a drastic enhancement in the microwave emissivity during the period. The passive
microwave emissivity continues to change as the snow cover continues to melt, gets saturated with
liquid and forms melt ponds in the summer. Further changes occur when bare ice gets frozen and then
starts to acquire a snow cover in early autumn. During this period of change in microwave emissivity
corresponding changes in surface albedo are also expected. Concurrent MODIS and AMSR-E data
are used to detect the exact time periods when the sea ice and its snow cover goes through the
various stages of development. In this study, the albedo of the surface is estimated and its variability is
assessed during the entire annual cycle to gain an understanding of the influence on albedo of the
changes in snow characteristics, thin sea ice, and different sea ice concentrations. This will be done
initially for the periiod 2002 to 2012 but will be extended for the period from 1981 to 2012 using a
combined AVHRR and MODIS data to be able to assess long term changes in the albedo that may be
associated with climate change.
Page | 466
1236
High-resolution surface structure of sea ice floes from terrestrial laser
scanning
1
1,2
3
1,4
Ernesto Trujillo , Katherine Leonard , Ted Maksym , Michael Lehning
1
2
CRYOS, ENAC, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland, Cooperative
Institute for Research in Environmental Sciences, University of Colorado, Boulder, United States,
3
4
Woods Hole Oceanographic Institution, Woods Hole, United States, WSL Institute for Snow and
Avalanche Research SLF, Davos, Switzerland
The use of Terrestrial Laser Scanning (TLS) in polar environments is becoming more frequent thanks
to its versatility and relatively low-cost operation required to obtain surface topographic information at
very high resolutions (1-10 cm). During the recent Australian-led SIPEX II (Sea Ice Physics and
Ecosystem eXperiment II) research voyage to East Antarctica (September-November 2012), the
morphology of snow/ice surfaces was captured through concurrent measurements from a Terrestrial
Laser Scanner and an automated snow probe. Integrated with the sea-ice draft measurements from
an Autonomous Underwater Vehicle (AUV), the resulting dataset provides a three-dimensional
characterization of sea ice floes at scales that are well suited for process-oriented research, moving
beyond the more traditional point-based measurements that are frequently taken in these extreme
environments. Here, we will describe the operational aspects of these surveys and will show how this
type of dataset can be used to analyze the spatial structure of the snow and ice surfaces at scales
between 1-cm and 100-m. Preliminary results indicate positively skewed distributions of sea-ice
surface elevations (~ 0.5), with two-dimensional correlation structures that are highly anisotropic
showing stronger correlations along the directions of the main dune-like features on the ice-floe
surfaces. Power spectrum analyses indicate that surface elevations are self-affine with spectral
exponents of the order of 1.9, consistent with the structure of fractional Brownian motion. These selfaffine characteristics appear evident in the field as spatial features in the snow/ice surfaces are
repeated across spatial scales, influenced by wind scouring and deposition of snow. Advantages and
challenges of the operation will be discussed, along with some of the improvements that the
integrations of such datasets offer for ice-floe-scale studies.
Page | 467
1028
Lagrangian tracking in sea ice model - design, implementation and applications
1
2
1,2
Shiming Xu , Jiping Liu , Bin Wang
1
2
Center of Earth System Science, Tsinghua University, Beijing, China, LASG, Institute of Atmospheric
Physics, Chinese Academy of Sciences, Beijing, China
In this work we propose the integration of Lagrangian tracking in Sea Ice model - CICE4-LASG, an
improved version of CICE4 by LASG. The on-line integration by carrying out Lagrangian tracking
alongside the Sea Ice model run enables high temporal resolution and hence better spatial accuracy
for the tracking of certain areas of Sea Ice. This allows detailed simulation of these interested areas of
Sea Ice, their dynamic and thermodynamic properties and life cycle. The implementation of
Lagrangian tracking is carried out in a parallelization-friendly manner by using existing primitives in
CICE4-LASG, to ensure high efficiency and good scalability over large-scale parallel machines. Also it
supports high-resolution simulation of up to 0.1 degrees with tri-pole grid. Comparison with historical
buoy tracks is carried out for the verification of the Lagrangian tracking module. Information of both
dynamics (buoy position, speed, etc.) and thermodynamics (ice thickness, radiation, temperature, etc.)
are used. Through experiments with 1 degree and 0.1 degree models, we show that the Lagrangian
tracking module is parallel-efficient, adding only marginal overhead to the exiting model, and it
accurately replays the record buoy movement. We further show that it can be used in various
applications, by applying it to the study of Sea Ice evolvement in both historical events and future
changes.
Page | 468
263
Energy dissipation in viscous-plastic sea ice models
1
1
Amélie Bouchat , Bruno Tremblay
1
Department of Atmospheric and Oceanic Sciences, McGill University, Montréal, Canada
In viscous-plastic (VP) sea ice models, small elastic deformations are approximated by viscous
deformations. Unlike elastic deformations, viscous deformations are irreversible and introduce a nonphysical energy dissipation. In fact, the amount of viscous points (and dissipation) increases with the
resolution and the number of outer loops of the numerical solver because the deformation lines are
getting better refined. In today´s high resolution and fully converged models, the validity of the VP
approximation is questioned.
To study the characteristics of energy dissipation in sea ice models, we derive an equation for the
kinetic energy (KE) balance by coupling the 2D momentum equation and the continuity equation for
sea ice thickness. This method applies to any rheology, but we focus on the classical VP model.
Results from a 40km-resolution run show that the main KE balance is between the atmospheric input,
the oceanic dissipation, and the internal stress term. It is found that one of the main roles played by
the internal stresses is to laterally redistribute the energy from the input regions to the deformation
lines. The energy is then stored as potential energy in ridges and dissipated by friction in ridging and
shearing.
On a monthly mean, the viscous frictional dissipation is found to be approximately a thousand times
smaller than the plastic frictional dissipation in all seasons. This suggests that the VP approximation is
valid on a monthly time scale. We explain this by the fact that the modeled plastic deformations
dissipate much larger amount of energy and occur more frequently than viscous deformations.
Preliminary results suggest that the previous results also hold for a 10 km resolution version of the sea
ice model. Results on the dependence of the energy dissipation on the degree of convergence of the
numerical solver will also be presented.
Page | 469
A5.4b - Asian glaciers and climate change
10.07.2013 10:15-11:45, Aspen II
183
Estimating volume of glacier stored water in Bhagirathi Basin, Himalayas using
surface velocity and slope
1
2
Prateek Gantayat , Anil V. Kulkarni
1
2
CAOS, IISc, Bangalore, India, Center For Atmospheric and Oceanic Sciences, IISc, Bangalore, India
The Himalayan Glaciers are a major source of water for the Indian sub-continent. Due to the rough
weather conditions and topography, field studies are limited. Therefore, scientists rely on classical
statistical methods to calculate velocity fields, depth and the total inventory of water present. One such
method is called the scaling method, where the depth is calculated by finding the total areal extent of
the glacier which is given as input to a power law relation between depth and area. But due to lack of
any physical basis the results are erroneous. In this project, we have estimated the velocity fields;
depth and the total water stored using NIR and SWIR bands of Landsat Imagery with 30 m spatial
resolution for the Gangotri glacier and have extended the analysis for the entire Bhagirathi basin which
has 238 glaciers. First, the velocity fields were calculated for the years 1999-2003 and 2009-2011,
th
using sub-pixel correlation where the error was 1/20 of pixel size. In this investigation, the images
acquired during the months of September and October were used because they have minimal
seasonal snow cover and are cloud free. The range of velocity field was estimated ~26 m/yr. near the
snout and ~80 m/yr. at the uppermost reaches of the glacier. The velocity vectors were directed along
the main trunk from accumulation to ablation region of the glacier and these values were further
validated with a field study at different locations. The modelled depth and water content were then
calculated using the equation of Laminar Flow which gives a relationship between depth and velocity
fields. The modelled depth was ~45 m at the snout and ~210 m in the uppermost region of the glacier.
Page | 470
298
Glacial surface lowering and development of formidable size lakes on debriscovered Imja and Chamlang-South glaciers in the Nepal Himalaya
1
2
2
1
Damodar Lamsal , Teiji Watanabe , Takanobu Sawagaki , Akiko Sakai
1
2
Environmental Studies, Nagoya University, Nagoya, Japan, Environmental Earth Science, Hokkaido
University, Sapporo, Japan
Recent studies have reported that debris-covered glaciers in the eastern Himalaya have been melting
leading to formation and expansion of glacial lakes, and have also caused threats to GLOFs. An
understanding of shrinkage of debris-covered glaciers is indispensable to estimating glacier mass
balance for water resource management and also to assessing potential hazard from glacial lakes.
Nevertheless, there are limited researches in the Nepal Himalaya, and thus little is known in this
regard. Aim of this paper is to document surface lowering of debris-covered Imja and Chamlang-South
glaciers and development of formidable size glacial lakes on them. Multi-date glacier surface
mappings with high-resolution satellite stereo-data over a longer span of time gap can produce reliable
information on surface lowering of glaciers and their surface retreat as a result of ponds/lake
expansion. High resolution Corona KH-4A (2.70-7.60 m) and Advanced Land Observing Satellite
(ALOS) PRISM (2.5 m) stereo-data taken in 1964 and 2006 were processed to generate digital terrain
models (DTMs) and then to derive glacial surface lowering. Average surface lowering of Imja Glacier
over four decades were found to be 16.9 m for the dead-ice area west of the lake, 82.3 m in the lake
area, and 47.4 m for the up-glacier surface east of the lake. While for Chamlang-South Glacier, the
average lowering of glacier was found to be 37.5 m. On the surface of these glaciers, there were few
2
supra-glacial ponds in 1964 which evolved to formidable size glacial lakes by 2010: 0.08 km to 1.12
2
2
2
km (Imja) and 0.04 km to 0.86 km (Chamlang-South). The glaciers which were almost intact by early
1960s were rapidly decayed and their terminus positions (active glacier) retreated approximately 2200
m (Imja) and 1700 m (Chamlang-South) by 2010.
Page | 471
337
Vulnerability of mountain glaciers to climate change and its projection in China
1
Jianping Yang
1
Cold and Arid Regions Environmental and Engineering Research Institute (CAREERI), Chinese
Academy of Sciences (CAS), Lanzhou, China
Glaciers in China, undergoing rapid de-glaciation since the 1990s, are an important water source of
China and adjoining countries. The adaptation to glacier change is urgent for these countries. The
objective of this study is to improve our understanding of glacial vulnerability so that the state
adaptation strategy can be established. A glacial numerical model is developed using spatial principle
component analysis (SPCA) method under the support of RS and GIS technologies. The model
contains nine factors including variables of topography, climate, and glacier. Using the model, the
situation of glacial vulnerability is evaluated integratedly during the period of 1961-2007 on a regional
scale. Based on the projection of air temperature and precipitation changes under the IPCC SERS
st
A1B scenario and of glacier change in the 21 century, glacial vulnerability is projected in the 2030s
and the 2050s using the same model. According to the numerical results, the vulnerability is classified
into five levels: potential, light, medial, heavy and very heavy level, following the natural breaks
st
classification (NBC). Glacial vulnerability distribution, its scenarios and changes in the 21 century are
analyzed and the factors of influencing glacial vulnerability are discussed. The results show that
mountain glaciers are very fragile to climate change in China, heavy and very heavy vulnerable zones
account for 41% of the whole glaciation area for the period 1961-2007. Glacial vulnerability shows a
declination trend in the 2030s and 2050s, but glaciers are still at heavy and very heavy vulnerability
levels in some regions. Topographical exposure and high sensitivity of glaciers to climate change are
responsible for glacial vulnerability in the period of 1961-2007. A change in precipitation is found to be
a crucial factor besides topographical factors in the 2030s and 2050s.
Page | 472
873
Surface mass balance of Potanin Glacier in Mongolian Altai since 2005
1
1
2
3
3
Keiko Konya , Tsutomu Kadota , Fumio Nakazawa , Davaa Gombo , Purevdagva Khalzan , Hironori
1
1
Yabuki , Tetsuo Ohata
1
2
3
JAMSTEC, Yokosuka, Japan, NIPR, Tachikawa, Japan, IMHE, Ulaanbaatar, Mongolia
The Mongolian Altai area has undergone few glaciological surveys and glacier mass balance studies.
Stake observations and pollen analysis with pit observations were used for the estimation of the
surface mass balance of the Potanin glacier in the Mongolian Altai. The mass balance was estimated
for the mass balance years since 2005. The observed less negative mass balance in 2005 and 2009
and more negative mass balance in 2008 were due to higher solid precipitation in 2004-2005 and
2008-2009 than in 2007-2008 and high summer temperatures in 2008 than in 2005 and 2009. A
comparison with Maliy Aktru Glacier in the Russian Altai, which is 100 km north to Mongolian Altai,
demonstrated that the two glaciers share the same tendency in mass balance fluctuation from 2005 to
2009. Potanin Glacier has a smaller accumulation area ratio (AAR) and higher equilibrium line altitude
(ELA) than Maliy Aktru Glacier. We concluded that the higher negative mass balance at Potanin
Glacier compared to Maliy Aktru glacier is due to 1) smaller AAR, 2) drier and warmer climate and 3)
longer response time to climate change.
Page | 473
875
Glacial lakes in the Indian Himalayas - From glacial lake inventories to
assessments of lake outburst risks
1
1
2
Raphael Worni , Markus Stoffel , Christian Huggel
1
2
Institute of Geological Sciences, University of Bern, Bern, Switzerland, Department of Geography,
University of Zurich, Zürich, Switzerland
Glacial lake hazards and glacial lake distributions are investigated in many glaciated regions of the
world, but so far, no glacial lake inventory existed for the entire Indian Himalayas. We therefore
compiled a first area-wide glacial lake inventory, including a qualitative classification at 251 glacial
2
lakes >0.01 km . Glacial lakes were detected in the five states spanning the Indian Himalayas and
were classified according to their relevancy to further assess the hazard situation.
Three glacial lakes, from different geographic and climatic regions within the Indian Himalayas were
then selected for a detailed risk assessment. Based on remote-sensing and field survey, key
parameters regarding the lake, dam and glaciated environment were assessed and potential lake
outburst scenarios defined. These lake outburst scenarios were then simulated with the dam-breach
and flood model BASEMENT.
The glacial lakes analyzed in the states of Jammu and Kashmir and Himachal Pradesh were found to
present moderate risks to downstream villages, whereas the lake analyzed in Sikkim was found to
severely threaten downstream locations. At the study site in Sikkim, a dam breach could trigger
6
3
3 -1
drainage of ca. 16 × 10 m water and generate maximum lake discharge of nearly 7,000 m s . Such
data facilitates the planning and dimensioning of accurate mitigation measures, and helps the
justification of decisions aimed at preventing infrastructure and populated areas from being possibly at
risk.
The analysis of mapped glacier lakes in the Indian Himalayas revealed that, in general, the hazard
situation emanating from glacier lakes is smaller in India than in other parts of the Hindukush
Himalaya. This, however, is not true for Sikkim where many unstable glacier lakes threaten
downstream locations and infrastructure. The detailed risk assessments of three potentially unstable
glacier lakes, point to the need for a further monitoring of these lakes.
Page | 474
776
Application of an energy balance model for a debris covered glacier in the
Nepalese Himalayas
1
1
1
1
2
Lene Petersen , Simon Wicki , Francesca Pellicciotti , Marco Carenzo , Walter Immerzeel
1
2
Institute of Environmental Engineering, ETH, Zurich, Switzerland, Faculty of Geosciences, Utrecht
University, Utrecht, Netherlands
Glaciers with debris-covered ablation zones are widely present in many mountain ranges such as the
Alps, the Himalayas and the Andes. An expansion of rock debris-covered areas has been documented
in recent decades, likely in association to a warming climate. The effect of varying debris thickness on
the glacier energy balance and on melt is often neglected in energy balance models, partly because
data on debris thickness are scarce, and thus simplified assumptions are commonly used.
In this study, we test a physically-based energy balance model recently developed over the debriscovered Lirung glacier, Nepal. The model considers the balance of heat fluxes at the air/debris
interface and heat conduction through the debris layer and it requires meteorological input variables
and specified debris thermal properties. Data to force and validate the model are provided by a field
campaign carried out from May to October 2012 on Lirung glacier. Data from an Automatic weather
station (AWS), air and surface temperature at numerous locations, effective conductivity and a large
data set of debris thickness measurements were collected. In a first step, the model is applied at the
point scale to recalibrate site-specific parameters and evaluate its sensitivity to the meteorological and
surface input. We show how the debris properties derived specifically for the glacier improve the
model performance compared to literature values. In a second step, a distributed model is applied
over the entire glacier. Different options to extrapolate meteorological forcings over the glacier area
are compared and results from spatial analysis of temperature are included. We use the model to
study spatial variability of melt rates over a debris covered glacier and quantify glacier-wide mean melt
values and compare to those of debris-free glaciers, as well as to study differences in the partition of
the energy fluxes between monsoon and non-monsoon season.
Page | 475
A2.2a - Coupling processes with hydrosphere (ocean) and cryosphere
10.07.2013 10:15-11:45, Forum
511
Vertical coupling from the top of the atmosphere to the bottom of the ocean
1
1
2
2
Thomas Reichler , Junsu Kim , Elisa Manzini , Juergen Kroeger
1
2
Univ. of Utah, Salt Lake City, United States, Max Planck Institute for Meteorology, Hamburg,
Germany
We provide evidence for an intriguing vertical coupling amongst the main components of the climate
system: stratosphere, troposphere, cryosphere, and hydrosphere. This evidence derives from
observations taken over the past 30 years and also from long time-slice simulations with coupled
climate models. The coupling manifests itself on long decadal time scales and seems to originate in
the stratosphere. At lags of several years it then creates self-sustained ocean oscillations associated
with the Atlantic Meridional Overturning Circulation. However, we find little evidence for a feedback of
the induced ocean oscillations into the extratropical atmosphere. We will discuss possible causes and
underlying physical mechanisms for the co-variability, describe its consequences for our
understanding of climate, and raise open questions regarding the new finding.
Page | 476
906
Stratosphere-troposphere coupling at interdecadal time scales
1
2
3
3
4
Elisa Manzini , Chiara Cagnazzo , Pier Giuseppe Fogli , Alessio Bellucci , Wolfgang Müller
1
2
Max-Planck-Institut für Meteorologie, Hamburg, Germany, Istituto di Scienze dell'Atmosfera e del
3
4
Clima, Rome, Italy, Centro Euro-Mediterraneo per i Cambiamenti Climatici, Bologna, Italy, Max
Planck Institute for Meteorology, Hamburg, Germany
Evidence of stratosphere-troposphere coupling at interdecadal time scales is searched for in a 260year simulation performed with a climate model. The boundary conditions of the simulation are
specified according to preindustrial conditions and are kept constant from year to year. It is shown that
long lasting (20 years) positive and negative anomalies of the northern winter stratospheric polar
vortex exist in the simulation. Given that there are no externally imposed low frequency time
variations, these persistent variations are due to internal dynamical processes of the modeled coupled
atmosphere ocean system. By composite analysis, it is shown that the long lasting stratospheric vortex
anomalies are connected through the troposphere to mean sea level pressure, surface temperature
and sea ice cover anomalies. These connections are reminiscent of intra-seasonal stratospheretroposphere coupling. Over the ocean, the surface temperature and sea ice cover anomalies are
indicative of the delayed Atlantic meridional overturning circulation response to atmospheric forcing.
The latter is indeed found to be anomalously strong/ weak during the long lasting positive/negative
stratospheric vortex anomalies, providing evidence for a potential role of the stratosphere in decadal
prediction.
Page | 477
881
Decada-scale co-variability in sea-ice extent between summer Arctic Ocean
and winter Okhotsk Sea
1
2
Bunmei Taguchi , Masayo Ogi
1
2
Earth Simulator Center, JAMSTEC, Yokohama, Japan, Research Institute for Global Change,
JAMSTEC, Yokohama, Japan
The sea ice extent (SIE) in the Okhotsk Sea—the southernmost of the seasonal sea ice formation
regions in the Northern Hemisphere—exhibits a distinct interannual-to-decadal variability as well as a
decreasing trend in recent decades. While the trend component is generally attributed to the global
warming, the cause of the oscillatory, low-frequency component of the Okhotsk SIE is unknown.
Analyzing a long- term coupled general circulation model (CGCM) simulation which represents distinct
decadal variability in SIC in the Okhotsk Sea, we show the wintertime Okhotsk Sea SIE variability is
tightly linked with the preceding summertime SIE variability over the marginal sea north of eastern
Siberia. This model result is in a good agreement with our separate analysis of observational and
reanalysis data, supporting the existence of the decada-scale co-variability in SIE between summer
Arctic Ocean and winter Okhotsk Sea. Further analysis reveals that it is the anomalous atmospheric
circulation over the east Siberia and the associated cold air advection in the late-fall season that
carries the decadal-scale memory of the summertime SIE variability in the Arctic Ocean to the Okhotsk
Sea remotely across the seasons from summer to winter.
Our analysis adds another example for the influence of the Arctic sea ice variability on midlatitude
climate to recent studies that showed the impact of reduced SIE in Arctic Barents Sea on the cooling
over Eurasian continent in the midlatitude due to enhanced Siberian High. Our study is distinct,
however, in that the center of action of the Arctic sea ice variability is located off east Siberia rather
than in the Barents Sea and that the reduced Arctic sea ice leads to cyclonic, as opposed to anticyclonic, circulation anomalies over the Siberia.
Page | 478
1215
Projected changes in Arctic summer storm-track activity by CMIP3 climate
models
1
1
2
Kazuaki Nishii , Hisashi Nakamura , Yvan J. Orsolini
1
2
RCAST, University of Tokyo, Tokyo, Japan, Norwegian Institute for Air Research (NILU), Kjeller,
Norway
Model performance and future projection of summer-time storm-track activity in the Arctic region and
associated climate components are investigated on the basis of Coupled Model Intercomparison
Project Phase 3 (CMIP3) climate models. Most of the models underestimate storm-track activity over
the Arctic Ocean measured locally as the variance of subweekly SLP fluctuations, and its large intermodel diversity is related to that of the lower-tropospheric westerlies in the Arctic region and the stormtrack activity over the entire extra-tropics. As a multi-model mean, the CMIP3 models project the
enhancement of storm-track activity over the Arctic Ocean off the eastern Siberian and Alaskan
coasts, the region called the Arctic Ocean Cyclone Maximum (AOCM), in association with the
strengthening of the westerlies projected in the warmed climate. This intensifying storm-track activity is
likely due to enhancing ocean-land contrast in surface air temperature (SAT) across the Siberian
coast, which reflects greater surface warming over the Siberian continent with increasing surface
sensible heat flux and slower warming over the Arctic Ocean with reduction in sea ice cover. The
projections of these variables nevertheless exhibit large inter-model variability, although their model
biases are correlated significantly in the same manner as among their multi-model means.
Page | 479
439
Snow cover dynamics and hdyrological regime of the source region of yellow
river basin, China
1
1
1
Jing Li , Shiyin Liu , Wanqin Guo
1
Cold and Arid Regions Environmental and Engineering Research Institute (CAREERI), Chinese
Academy of Sciences (CAS), Lanzhou, China
A part proportion of flow in the Yellow river is contributed by its snow- and glacier-fed river catchments
in the Source area. It is therefore essential to understand the cryosphere dynamics in this area for
water resource management. The MODIS MOD10A2 remote-sensing database of snow cover
products from March 2000 to December 2012 was selected to analyse the snow cover changes in the
source region. A database of monthly flows for the source area over a period of 40 yr and climate data
(precipitation and temperature) from meteorological stations within the catchment was made available
to investigate the hydrological regime in the area. Analysis of remotely sensed cryosphere suggest a
shrink of glacier in the area. The increase in snow cover may be the result of an increase in winter
precipitation caused by westerly circulation. The increasing of runoff most cause by the rising
temperature causing the more melt water.
Page | 480
C2.1a - Dynamics and impact of ice formation in clouds
10.07.2013 10:15-11:45, Studio
369
Results and implications derived from measurements of different types of ice
nuclei with the Leipzig Aerosol Cloud Interaction Simulator
1
2
3
3
2
1
Heike Wex , Paul DeMott , Hinrich Grothe , Bernhard Pummer , Yutaka Tobo , Stefanie Augustin ,
1
1
1
1
1
Tina Clauss , Susan Hartmann , Dennis Niedermeier , Michael Raddatz , Jens Voigtlaender , Frank
1
Stratmann
1
2
Institute for Tropospheric Research, Leipzig, Germany, Colorado State University, Department of
3
Atmospheric Science, Fort Collins, United States, Vienna University of Technology, Institute of
Material Chemistry, Vienna, Austria
Ice containing clouds permanently cover 40% of the earth's surface and have a large influence on
both, weather and climate. Therefore, understanding the processes that form ice in these clouds are
important. It is known that there are two main pathways of atmospheric ice formation, namely
homogeneous and heterogeneous ice nucleation. The latter involves aerosol particles that act as ice
nuclei (IN), and these IN can be e.g. dust particles or biological particles like bacteria, pollen and
fungal spores. Different heterogeneous freezing mechanisms do exit, with their relative importance for
atmospheric clouds still being debated. However, there are strong indications that immersion freezing
is one of the important or maybe even the most important mechanism when considering mixed phase
clouds (Murray et al., 2012).
What we are still lacking is a) the fundamental process understanding on how aerosol particles induce
ice nucleation and b) means to quantify ice nucleation in atmospheric models. Concerning a) there
most likely is not only one answer, considering the variety of IN found in the atmosphere. With respect
to b) different approaches have been suggested. However it is still being debated which would be a
suitable way to parameterize laboratory data for use in atmospheric modeling.
In this presentation, both topics will be addressed. Using the Leipzig Aerosol Cloud Interaction
Simulator (LACIS) (Hartmann et al., 2011), we examined different types of dust particles with and
without coating, and biological particles such as bacteria and pollen, with respect to their immersion
freezing behavior. We will summarize our findings concerning the properties controlling the ice
nucleation behavior of these particles and present means for parameterizing their respective ice
nucleation behavior.
References:
Hartmann et al. (2011), Atmos. Chem. Phys., 11, 1753-1767.
Murray et al. (2012), Chem. Soc. Rev., 41, 6519-6554.
Page | 481
1025
Heterogeneous ice nucleation of crystalline sodium chloride dihydrate
particles
1
1
Ottmar Moehler , Robert Wagner
1
Karlsruhe Institute of Technology, Karlsruhe, Germany
Super-micron-sized sodium chloride dihydrate (NaCl 2 H2O) particles deposited onto a surface were
observed to be ice-active in the deposition mode at temperatures below 238 K, with a median
threshold ice saturation ratio of only 1.02 in the temperature range from 238 to 221 K (Wise et al.,
Atmos. Chem. Phys., 12, 1121-1134, 2012). We have used the AIDA cloud chamber to also
investigate the ice nucleation behaviour of crystalline sodium chloride dihydrate particles, but in the
aerosol state with particle diameters in the range from about 0.3 to 3 µm and a number mode diameter
around 1 µm. In these AIDA cloud expansion experiments heterogeneous ice nucleation was first
detected at a temperature of 227.1 K with a concomitant threshold ice saturation ratio of 1.25. Above
that temperature, the crystalline salt particles underwent a deliquescence transition to form aqueous
NaCl solution droplets upon increasing relative humidity. The deliquescence occurred before reaching
the ice supersaturation threshold for deposition mode ice nucleation, therefore suppressed the
occurrence of heterogeneous ice nucleation. At nucleation temperatures below 225 K, the inferred
threshold ice saturation ratios varied between 1.15 and 1.20. The number concentration of the
nucleated ice crystals was related to the surface area of the crystalline aerosol particles to deduce the
ice nucleation active surface site (INAS) density of the aerosol population as a function of the ice
10
-2
supersaturation. Maximum INAS densities of about 6×10 m at an ice saturation ratio of 1.20 were
found for temperatures below 225 K. These INAS densities are similar to those recently derived for the
deposition mode ice nucleation on mineral dust particles.
Page | 482
972
Extent and relevance of stacking disorder in atmospheric ice crystals
1
1,2
1
2
Werner F. Kuhs , Christian Sippel , Andrzej Falenty , Thomas C. Hansen
1
2
GZG Abt. Kristallographie, Universität Göttingen, Göttingen, Germany, Institut Laue-Langevin,
Grenoble, France
A solid water phase commonly known as ”cubic ice”, or ”ice Ic”, is frequently encountered in various
transitions between the solid, liquid and gaseous phases of the water substance. It may form e.g. by
water freezing or vapour deposition in the Earth's atmosphere. It can form in a wide temperature range
from about 120 K up to at least 240K (in some cases up to the melting point), i.e. the range of interest
for cirrus clouds. Ice crystals formed in the laboratory directly from the gas phase under relevant
atmospheric conditions exhibit numerous stacking faults (as evidenced by our diffraction experiments)
and are neither truly cubic nor hexagonal in shape (as evidenced by electron microscopy). Rather,
they exhibit trigonal symmetry and have multiple kinks in their prismatic planes. These imperfections
may explain the observed higher vapour pressure over “cubic ice”; the kinks of the ice crystals' surface
will have a considerable influence on their backscattering properties and their chemical reactivity [1].
We emphasize that such defective ice crystals will be the normal encounter in many cirrus cloud as
there is no evidence that normal ice hexagonal ice crystals can formed below about 200K! Moreover,
once formed, this defective ice can persist up to 240K [2]. We followed the evolution of the stacking
disorder as a function of time and temperature at conditions relevant to atmospheric processes: A
continuous transformation towards normal hexagonal ice, ice Ih, is observed; however, the annealing
is very incomplete below 200K and becomes very rapid only when approaching 240K. In the
temperature-range from 180 to 200K a significant annealing of the imperfections takes place on
timescales of hours, i.e. timescales similar to the lifetime of cirrus clouds [1].
[1] Kuhs et al (2012) PNAS 109, 21259.
[2] Kuhs et al (2004) PCCP 6, 4017.
Page | 483
131
Characterization of water accommodation and desorption from a precursor
state on ice with implications for cloud processes
1
2
1
1
Xiangrui Kong , Panos Papagiannakopoulos , Erik Thomson , Jan Pettersson
1
2
University of Gothenburg, Gothenburg, Sweden, Department of Chemistry, University of Crete,
Heraklion, Greece
Many details in the development of ice clouds in the atmosphere remain poorly understood. Processes
as basic as water accommodation on ice are poorly constrained by earlier studies that show variations
over three orders of magnitude. Here we investigate the kinetics of water uptake and desorption from
pure ice surfaces at temperatures from 180 to 200 K. An environmental molecular beam method is
employed where short pulses of D2O gas collide with H2O ice and the subsequent desorption of D2O is
monitored by mass spectrometry. One fraction of the incoming water flux is lost by incorporation into
the ice structure and the temperature dependence of the accommodation coefficient is determined.
Other molecules are thermally desorbed from the surface and surface residence times of tens of
milliseconds are directly observed. The desorption follows first order kinetics and calculated Arrhenius
parameters are indicative of a weakly bound state for water on the ice surface. This weak initial
bonding places a limit on water uptake and incorporation by the ice. The results are compared with
literature data and the implications for ice processes in the atmosphere are discussed.
Page | 484
529
Surprises in hailstone physics
1
Roland List
1
Department of Physics, University of Toronto, Toronto, Canada
The first mathematical theory of the heat and mass transfer of spherical hailstones by Schumann was
based on four variables: air (tA) and surface (tS) temperature, liquid water content Wf and Re or
equivalent. In 1960/63 List added a fifth, the ice fraction If of the accreted spongy deposit, and in 2013,
elevated the net collection efficiency ENC from 'adjusting parameter' to 'variable' - equivalent to Re, Wf
and If. This constellation allowed a consolidation of the six variables into four new ones, realizing that
Re and Wf act as pair only, similar to ENC and If. Further, hail growth was categorized into three
scenarios: the 'old' dry growth and two involving shedding without (Case 2) and with water skins (Case
3). Replacing Re by the hailstone diameter D by using the free fall relationship in a height-air pressuretemperature-coupled atmosphere further enhances understanding. Setting bounds for the range of
variables led to a compact representation of all variable combinations in diagrams never assembled
o
o
o
before. The lowest surface temperatures are: -31 C for dry growth, >-0.55 C for Case 2 and >-5 C for
Case 3. The highest accretion rates occur under shedding with 0.2< ENCIf< 0.6. Shedding occurs only
from hailstones experiencing spongy growth. Shedding is the nearly exclusive growth mode. Growth
speeds are about double for shedding hailstones because Wf is allowed to double in accordance with
accumulation zones, identified by Doppler radar observations of packaging of falling hail.
Shedding is important because it initiates and maintains the evolution of warm rain parallel to and
interacting with hail growth.
Page | 485
50
Dynamics of aerosol ice-forming efficiency variability formed by different
generator types under the conditions close to natural ones
1
1
1
1
2
Aleksei Shilin , Alexander Drofa , Vladimir Ivanov , Anatoly Savchenko , Daniel Martines-Castro ,
2
3
Carlos Peres-Sanches , Valentin Shilin
1
2
Cloud Physics, FSBI “RPA “Typhoon”, Obninsk, Russian Federation, Instituto de Meteorología, La
3
Habana, Cuba, Trustedsafe GmbH, Berlin, Germany
Generators of ice-forming aerosol for indirect introduction of an agent into a supercooled medium are
widely used, and active particles are present in the atmosphere for a long time. Under these conditions
the main problems are the of ice-forming efficiency variability of such aerosols with time. To study
these effects the experiments were carried out at the RPA “Typhoon” for measurements of aerosol iceforming efficiency. Three different types of generators were studied:
1. The ground-based liquid-fuelled aerosol generator;
2. The standard 8% AgJ pyrotechnic composition (for anti-hail missiles, cartridges, flares,
pyrotechnic ground-based generators );
3. The experimental composition with a small silver content and a high iodide content. The ratio
of silver iodide to the iodizing addition provides a wide range of solution concentrations at
which silver iodide isabsent in solid phase and there are no break-down factors (surface
ageing, adsorption of admixtures, UV-radiation).
In contrast to aerosol formed in systems 1-2, the following principal differences are typical of aerosol
with a considerable prevalence of the iodizing addition:
•
•
•
•
The existence of non-active state of particles after the moment of aerosol formation without
break-down processes;
Maximum activity in some range of humidity and temperature;
A possibility of ice-forming properties recovery in low humidity zone;
Such properties may be controlled by varying composition.
The experiments were carried out with a specially designed stand ensuring studies of generators
operation in the conditions maximally close to the reality. During the experiments studied were the
effect of humidity, temperature on aerosol ice-forming efficiency. The properties of particles generated
by composition (3) drop to a significantly lesser extent.
There are several advantages in the situations when aerosol should not be introduced directly into a
supercooled medium.
Page | 486
B3.1e - General dynamics
10.07.2013 10:15-11:45, Wisshorn
554
Numerical reproduction of 6 May 2012 Tsukuba tornado and effect of warm
ocean current on its formation environmental fields
1
2
Teruyuki Kato , Wataru Mashiko
1
2
Meteorological Research Institute, Tsukuba, Japan, Meterological Research Institute, Tsukuba,
Japan
On 6 May, 2012, a strong tornado with Fujita scale 3 struct Tsukuba city, located middle part of Japan.
In this study, the tornado and a supercell storm causing it were able to be reproduced just by
dynamically downscaling from mesoscale analysis data of the Japan Meteorological Agency
(horizontal resolution: 5 km) to a grid size of 50 m. No additional observations were assimulated in this
numerical simulation. The tornado with the maximum vorticity of 1.6/s and the maximum wind speed
exceeding 65 m/s was generated at the hook echo tip over a gust front, coresponding with the
fromation process of typical supercell tornadoes. The enhancement of rear-flank downdraft, especially
associated with the hook echo, could be fundamentally crtical to the tornadogenesis.
The analysis on environmental fields indicated that the northward inflow of low-level humid air over the
Pacific Ocean was the main factor for the formation of the supercell storm. The specific humidity at a
height of 500 m became almost doubled from 6 g/kg during 12 hours when the low-level air traveled
over the ocean south of the Japanese Islands. The increase could be mainly caused by updrafts
associated with a low-level short trough travelling eastward. The effect of warm ocean current “Japan
Current” on the increase was examined from a sensitivity experiment in which the maximum sea
surface temperature was set under 20 degrees of Celsius, because the route of the low-level air
almost corresponded with the location of the current. In the control experiment compared with the
sensitivity, the pressure drop over the current accelerates low-level horizontal winds, causing the
increase of latent heat flux from the ocean and the enhancement of updrafts over the short trough.
Consequently, the low-level air obtains additional 2 g/kg, which is one-third of the increase.
Page | 487
720
Diabatic Rossby vortex genesis associated with recurving tropical cyclones
1
1
1
Richard Moore , Heather Archambault , Patrick Harr
1
Naval Postgraduate School, Monterey, United States
A diabatic Rossby vortex (DRV) is a short-scale, diabatically dominated moist baroclinic cyclone that
grows in the absence of significant upper-level forcing. DRVs are ubiquitous, have been linked to a
number of high-impact weather events, and are notoriously difficult to predict.
One distinct avenue to DRV genesis is associated with recurving tropical cyclones (TCs). In this
scenario, diabatic processes are initiated along a baroclinic zone in response to the impinging warm,
moist flow associated with the TC circulation. The goal of this work is to investigate this scenario via a
10-year climatology of DRV genesis associated with recurving TCs over the western North Pacific and
an in-depth examination of a representative case study.
The climatological analysis is based upon the climatology of DRV occurrence prepared by Boettcher
and Wernli (2013) and the recurving TC climatology of Archambault et al. (2013). The frequency of
DRV genesis in response to recurving TCs is established and the characteristic environmental
conditions are explored via composite analysis. The case study is related to recurving North Pacific TC
Chaba in October 2010. A high-amplitude DRV was observed to the northeast of Chaba along the
midlatitude baroclinic zone in a region of frontogenetically forced precipitation. Upon interacting with a
pre-existing extratropical cyclone, the storm system underwent rapid intensification over the eastern
North Pacific. A number of high-impact weather events were observed downstream over North
America. The role of the DRV as a precondition of the subsequent high-impact weather is explored.
Page | 488
416
Moist baroclinicity: a unifying perspective on polar low development
1
2
3
Annick Terpstra , Thomas Spengler , Richard W. Moore
1
2
Geophysical Institue, University of Bergen, Bergen, Norway, Geophysical Institute, University of
3
Bergen, Bergen, Norway, Department of Meteorology, Naval Postgraduate School, Monterey, United
States
Current ideas on the dynamical processes associated with polar low development are diffuse:
postulated theories cover a broad spectrum between baroclinicity and convection, and the dynamical
importance of upper level features during polar low development remains unclear.
A potential dominant forcing mechanism for polar lows is the the so-called Diabatic Rossby Vortex
(DRV). A DRV consists of a solitary low-level vortex developing in a moist baroclinic environment, its
growth rate depending both on the moisture content and baroclinicity. To gain insight into the
dynamics of polar lows, we hypothesize that a significant fraction of polar low formation and
intensification events is captured by this mechanism.
The advantage of the DRV mechanism over the currently proposed mechanism for polar low
development is that it is a coherent dynamical structure based on both baroclinic and convective
processes, and as it is independent of the far field the presence of an upper level disturbance in not
essential.
To evaluate the applicability of the DRV mechanism to polar low development the WRF model is
utilized. The setup is composed as an idealized baroclinic channel constituting environmental
baroclinicity defined by a zonal jet and moisture content defined by relative-humidity profiles. Initiation
of the polar low is achieved by superimposing a small, warm-core, cyclonic surface disturbance to the
setup. This tool enables us to evaluate the DRV mechanism in the whole range of environmental
conditions known to be conducive for polar low development.
The experiments are evaluated in terms of typical structural characteristics of the DRV and realistic
polar low development on temporal and spatial scales. The relative importance of the generation of
eddy available potential energy by diabatic versus baroclinic processes is used to differentiate
between the dynamical processes contributing to disturbance growth.
Page | 489
866
Classification of cyclogenesis events based on a set of precursors
1
1
1
Michael Graf , Michael Sprenger , Heini Wernli
1
ETH Zürich, Institute for Atmospheric and Climate Science, Zurich, Switzerland
Many studies indicate a large variability of the relevant physical processes (so-called precursors)
responsible for cyclogenesis. In this tudy, potential precursors for cyclogenesis are systematically and
comprehensibly investigated on a statistical basis. For this reason, cyclones are objectively identified
during 2006-2010 in the ERA-interim dataset and then tracked along their life cycle. The starting points
of these tracks, i.e. the cyclones´ genesis, are further investigated.
In the environment of these locations a set of about 25 precursors is determined. The set includes the
following parameters: (a) the surface conditions and fluxes (e.g. sensible and latent heat fluxes, sea
surface temperature); (b) characteristic conditions in the troposphere (e.g. integrated water vapor,
amplitude of low-level potential vorticity); (c) measures of baroclinic and convective stability (e.g.
horizontal temperature gradients, convective available potential energy, Eady growth rate); and (d)
flow patterns and forcings from upper-tropospheric and stratospheric levels (e.g. jet streams and
streaks, potential vorticity anomalies, height of the tropopause).
Note, in addition to simple Eulerian characterisations, more advanced diagnostic approaches are
applied: Lagrangian backward trajectories, averaged time since oceanic moisture uptake of involved
low-level air parcels and quasigeostrophic omega forcing.
Based on these parameters, determined for a multitude of cyclones, a clustering analysis is performed
to categorize the different cyclogenesis events. It is expected to reproduce the classification of
Petterssen and Smebye, but also to substantially extend it to several subcategories. Furthermore,
composites of the cyclogenesis environment of each category will be shown for different parameters.
Page | 490
466
The sporadic nature of meridional heat transport by transient eddies
1
1
Gabriele Messori , Arnaud Czaja
1
Physics, Imperial College London, London, United Kingdom
The study analyses meridional atmospheric heat transport, due to transient eddies, in the European
◦
Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis. Daily, 0.7 latitude and
longitude resolution data at the 850 mb pressure level are used. Probability density functions (PDFs)
of meridional transient-eddy heat transport display a near-zero most likely value and a very large
skewness, which highlights the dominant role played by extreme events. When considering zonal
sections, in both the Northern and Southern Hemispheres, events in the top five percentiles typically
contribute to over half of the net poleward transport. As a result of this sensitivity to extremes, a large
fraction of the heat transport by transient eddies, at a given location and season, is realised through
randomly spaced bursts (a few per season), rather than through a continuum of events.
The predominance of extreme events can be explained by the favourable phase relationship between
meridional velocity and moist static energy temporal anomalies. This and the spatiotemporal
characteristics of the events are compatible with Eady-type growing systems.
Page | 491
D1b - Economics of weather and climate risks
10.07.2013 10:15-11:45, Schwarzhorn
380
Insuring against catastrophic weather risks in agriculture
1
1
Raushan Bokusheva , Sarah Conradt
1
Agri-Food and Agri-Environmental Economics Group, Institute for Environmental Decisions, ETH
Zurich, Zürich, Switzerland
In recent decades index-based insurance has been considered as a valuable alternative for traditional
crop insurance. The main advantage of the former is that it is better suited to combat asymmetric
information problems, i.e. adverse selection and moral hazard. An additional important advantage of
index-based crop insurance is its capacity for reducing transaction and administrative costs that
facilitates fast claim settlement. This characteristic of index-based insurance makes it particularly
relevant in the context of the catastrophic events' management when disaster relief payments must be
provided to a large number of affected farmers within a very short period of time.
In this paper we evaluate the effectiveness of index-based insurance designed to protect against
catastrophic events. By employing two alternative methods - the standard regression analysis and the
copula approach, we investigate the potential of making insurance more effective in terms of risk
reduction and more affordable regarding insurance premium level. In our study we define the
catastrophic drought insurance as an insurance which pays the indemnity if the index chosen to
indicate the drought occurrence falls below the third decile qo.3 of its probability distribution.
Our study employs wheat yield, weather and satellite data for 47 large grain producers from the
Northern Kazakhstan. Indices considered in the analysis are weather indices such as cumulative
rainfall (CR) and days of crop drought stress (DCDS), and so called vegetation condition index (VCI)
derived by utilizing satellite data.
Page | 492
1036
Accounting for different uncertainties and implications for climate investments
1
Svenja Hector
1
Department of Management, Technology and Economics, ETH Zurich, Zurich, Switzerland
The discount factor applied to future consumption is a key determinant of the optimal investment for
climate change mitigation and adaptation. The presence of uncertainty about the future as well as a
decision maker´s risk aversion may affect the discount factor positively or negatively. This paper
clarifies the link between risk aversion and optimal investment policies. I show that the direction of the
effect of an increase in risk aversion on the discount factor depends crucially on the type of uncertainty
accounted for. To this end, I introduce a general framework that can cope with very different forms of
uncertainty. The results highlight that whether an increase in risk aversion affects the discount factor
positively or negatively depends on some fundamental properties of the uncertainty taken into
account.
Page | 493
44
Adaptation to cyclone risk: evidence from the global cross-section
1
2
Solomon Hsiang , Daiju Narita
1
2
Princeton University, Princeton, United States, Kiel Institute for the World Economy, Kiel, Germany
Understanding the feasibility and cost of adaptation is essential to management of the global climate.
Unfortunately, we lack general estimates of adaptive responses to almost all climatological processes.
To address this for one phenomenon, we estimate the extent of adaptation to tropical cyclones (TCs)
using the global cross-section of countries. We reconstruct every TC observed during 1950 exposure.
We then look for evidence of adaptation by comparing deaths and damages from physically similar TC
events across countries with different TC climatologies. We find that countries with more intense TC
climates suffer lower marginal losses from an actual TC event, indicating that adaptation to this
climatological risk occurs but that it is costly. Overall, there is strong evidence that it is both feasible
and cost-effective for countries with intense TC climatologies to invest heavily in adaptation. However,
marginal changes from countries TC climates generate persistent losses, of which only -2008 to
parameterize countries' TC climate and year-to-year TC' currentt ~3% is “adapted away” in the long
run.
Page | 494
C5.2b - Changing snow and ice hydrology in mountain watersheds
10.07.2013 10:15-11:45, Seehorn
1264
Comparing a distributed temperature-index and energybased model in
mountainous watershed
1
2
3
4
2
Mukesh Kumar , Danny Marks , Jeff Dozier , Michele Reba , Adam Winstral
1
2
Nicholas School of Environment, NC, United States, USDA Agricultural Research Service, Boise,
3
United States, Bren School of Environmental Science & Management, University of California, Santa
4
Barbara, Santa Barbara, United States, Watershed Physical Processes Research Unit, USDA
Agricultural Research Service, Oxford, United States
Two commonly used strategies in modeling snowmelt are the energy balance and temperature-index
methods. Here we evaluate the distributed hydrologic impacts of these two different snowmelt
modeling strategies, each in conjunction with a physics-based hydrologic model (PIHM). Results
illustrate that both the Isnobal energy-balance and calibrated temperature-index methods adequately
reproduce snow depletion at the observation site. However, the models exhibit marked differences in
the distribution of snowmelt. When combined with PIHM, both models capture streamflow reasonably
during calibration year (WY06), but Isnobal model gives better streamflow results in the validation year
(WY07). The uncalibrated temperature-index model predicts streamflow poorly in both years.
Differences between distributed snow melt as predicted by Isnobal and calibrated temperature-index
method, and its consequent affect on streamflow prediction suggests the need to carefully calibrate
temperature-index models in both time and space.
Page | 495
686
The effect of canopy gaps on incoming radiation at the snow surface and
implications for snowpack retention in forested regions
1
2
2
3
4
5
Timothy Link , Chad Ellis , John W. Pomeroy , Robert R. Lawler , Richard Essery , Danny Marks
1
2
College of Natural Resources, University of Idaho, Moscow, United States, Geography & Planning,
3
University of Saskatchewan, Saskatoon, Canada, U. S. Forest Service, Colville, United States,
4
5
School of GeoSciences, University of Edinburgh, Edinburgh, United Kingdom, Northwest Watershed
Research Center, USDA Agricultural Research Service, Boise, United States
In mountainous, forested environments, vegetation exerts a strong control on snowcover dynamics
that in turn affect ecohydrological processes, streamflow regimes, and riparian health. Snowcover
deposition and ablation patterns in forests are controlled by a complex combination of canopy
interception processes coupled with radiative and turbulent heat flux patterns related to topographic
and canopy cover variations. In most seasonal snow environments, snowcover ablation dynamics in
forests are dominated by net radiation. Recent research indicates that in small canopy gaps, an allwave incoming radiation minima relative to both open and forested environments can occur, but
depends strongly on solar angle, gap size, slope, canopy height and stem density. The optimal gap
size to minimize radiation to snow was estimated to have a diameter between 1 and 2 times the
surrounding vegetation height. Physically-based simulations of snowpack dynamics at a high-latitude
site indicate that gaps may increase SWE and desynchronize snowmelt by approximately 3 weeks
between north and south facing slopes, relative to undisturbed forests. On east and west facing
slopes, small gaps cause melt to be slightly delayed relative to intact forests, and have a minimal
effect on melt synchronicity between slopes. These results indicate that forest gap thinning may be
used to reduce snowmelt rates and/or alter melt synchronicity, but the exact configuration will be
highly spatially variable. Development of management strategies to conserve water on the landscape
to enhance forest and riparian health in a changing climate, must also rigorously evaluate the effects
of specific hydrometeorological conditions on net radiation, turbulent fluxes, and snow interception
processes.
Page | 496
997
Rain on snow: the impact of climate warming on the spatial variability of snow
and mountain hydrology
1
1
2
3
4
Danny Marks , Adam Winstral , Tim Link , Michele Reba , Mukesh Kumar
1
2
USDA-ARS-NWRC, Boise, United States, Forest Science, University of Idaho, Moscow, United
3
4
States, National Sedimentation Laboratory, USDA-ARS, Jonesboro, United States, Nicholas School
of Environment, Duke University, Durham, United States
The hydrology of mountain regions is determined by precipitation phase, volume and distribution. The
complexities of precipitation volume and distribution are the result of a complex interplay between
regional orographic effects, and local-scale wind field interaction with vegetation and topographic
structure. Air-mass characteristics interact with the elevation range of mountain systems to determine
the precipitation phase and the elevation of the rain-snow transition. The makeup of forest and river
systems in mountain basins is a reflection of the stability of the rain-snow transition elevation over a
long period of time. However, in a rapidly changing and warming climate, the rain-snow transition is no
longer stable, and is moving to higher elevations. This continues to have a dramatic impact on
mountain hydrology, streamflow, and our ability to predict water supplies from mountain regions. As an
example of how dynamic these changes can be we present a combination of measurements and
simulation of conditions during a major rain-on-snow event that occurred between Dec 25, 2005 and
2
Jan 1, 2006, over an 800m elevation range in a 14 km mountain catchment. During the event, 174
mm of precipitation fell on the basin, representing approximately 20% of the water year total
precipitation, with multiple transitions between rain and snow along the elevation gradient. This event
illustrates the potential impact a warmer climate may have on mountain hydrology and streamflow in
western North America.
Page | 497
378
Snow cover variation over Turkiye
1
2
3
Ahmet Tekeli , Ibrahim Sonmez , Erdem Erdi
1
2
Civil Engineering, King Saud University, Riyadh, Saudi Arabia, Department of Meteorology, Ondokuz
3
Mayıs University, Samsun, Turkey, Remote Sensing Division, Turkish State Meteorological Service,
Ankara, Turkey
Rivers originating from the mountainous regions in Tϋrkiye mainly get their water from the melting of
snow accumulated during the winter time on these mountains. Thus monitoring snow cover and its
variation is important for accurate water resources management. Despite the importance of snow
cover there is no operational snow cover monitoring over Tϋrkiye, yet and limited information is
available by the in-situ observations about the snow cover variation.
In this study, daily snow cover data from interactive multisensor snow and ice mapping system (IMS)
by NOAA/NESDIS is used to examine the snow cover trend over Turkey. The daily IMS data and insitu snow depth measurements from 219 synoptic and climate stations covering 2004-2011 period are
used as ground truth data.
Initially, validation of IMS product is performed and contingency tables including the categorical
statistics of probability of detection (POD) and false alarm rate (FAR) are derived in daily and seasonal
basis. The POD value of 0.723 and FAR value of 0.208 is obtained for the whole study area of
Tϋrkiye. The same statics are derived for the seven geographical sub-regions of Tϋrkiye to introduce
the spatial variation of the product accuracy. The highest POD amount, 0.801, is obtained for the
Eastern Anatolia Region and the lowest, 0.451, is seen in South-Eastern Anatolia Region.
Non-parametric test of Mann-Kendall is performed to examine trend presence for the snow cover. The
test results with significance level of 0.05 indicated that both the whole domain (Tϋrkiye) and all the
sub-regions indicated negative trend. Significantly positive trend is obtained for Tϋrkiye and all subregions for the autumn season. On the other hand, negative trend is obtained for the same regions in
spring and summer seasons. For the winter season, only the Aegean Region, indicated positive while
all the others indicated negative trend.
Page | 498
1048
Soil temperature and water dynamics on contrasting aspects in the rain-snow
transition zone
1
2
2
Mark Seyfried , Tim Link , Sage Bryden
1
2
USDA-ARS-NWRC, Boise, United States, Forest Science, University of Idaho, Moscow, United
States
Understanding how complex terrain affects hydrological and biogeochemical processes has become
increasingly important as the global climate changes. Soils modulate both fluxes and are therefore
central to this understanding. We are particularly interested in soil temperature and water content
because they exert strong controls on hydrologic and biogeochemical fluxes. We measured soil water
(θ) and temperature (Ts) profiles at three paired locations in mountainous, complex terrain in SW
Idaho, USA (~43°latitude). Each pair consisted of a soil profile of temperature and water content from
a depth of 5 cm to bedrock (50 to 110 cm) on opposing north and south facing slopes at the same
elevation. The sites are located near the rain/snow transition elevation for the area (1600 m) on steep
slopes (25 to 40°) with sparse vegetative cover. We measured dramatic differences between the two
slopes, with a difference of 9°C (at 50 cm) in August. Differences between slopes were smaller in
winter, about 4° C. The Ts difference between two opposing slopes at identical elevations that we
measured is practically the same as the difference between Ts measured on nearly level ground but
separated by 1000 m in elevation. This implies that we need to consider two snowmelt seasons within
a given watershed based on aspect. We expected θ on north facing soils to decline more slowly and
later in the year the south facing soils due to the evaporative demand differential. We did not observe
this and, in fact, θ on the two slopes responded similarly during spring and early summer. This is
attributed to two factors. First, spring rains were sufficient to maintain relatively high soil water storage
on both slopes. Second, the denser vegetative cover on the north-facing slopes counters the lesser
evaporative demand.
Page | 499
B7.1b - Atmosphere Ocean and Cryosphere Interactions - BCI
10.07.2013 10:15-11:45, Sertig
702
Recording the atmospheric Anthropocene (I) - what are we getting?
1
James Butler
1
Global Monitoring Division, NOAA Earth System Research Laboratory, Boulder, United States
If we define the anthropocene as the recent period when humans are leaving remarkable records of
their presence on this planet, we find that we have very little in the way of consistent, real-time
measurements of atmospheric composition to document our influence. Many of these records,
however, have been obtained over the past few decades with extraordinary precision and diligent
attention to accuracy, such that they have been able to identify subtle phenomena and impacts of
human behavior already. These would include recent histories of increasing greenhouse gases,
ozone-depletion and the trace compounds responsible for it, aerosol composition, and other markers
of our existence. The records are useful for understanding the impacts of our behavior and offering
ways to mitigate them. They also offer tools for differentiating between impacts of human behavior and
those of Earth-system variability. Finally, having such high quality records allows us to better
understand the processes whereby they are recorded in snow and ice. This has a direct impact on
how we interpret existing records from the past and allows us to detect subtle (and some not-sosubtle) processes in capturing atmospheric records in ice.
Page | 500
294
pH evolution in the sea ice environment and implications for troposphericcryospheric chemistry over polar oceans
1
1
1
1,2,3
Feiyue Wang , Alexander Hare , David Barber , Soren Rysgaard
1
2
Centre for Earth Observation Science, University of Manitoba, Winnipeg, Canada, Greenland
3
Climate Research Centre, Greenland Institute of Natural Resources, Nuuk, Greenland, Arctic
Research Centre, Aarhus University, Aarhus, Denmark
The discoveries of springtime tropospheric bromine explosion, ozone depletion and mercury depletion
events over the polar oceans suggest a strong coupling of tropospheric chemical processes with those
occurring in the sea ice environment. The current understanding of these events requires an acidic
sea ice surface and/or frost flowers where seawater bromide becomes volatile and subsequently
photochemically activated. Here we report the first direct measurements of pH evolution in outdoor
experimental sea ice at the Sea-ice Environmental Research Facility (SERF) in Winnipeg, Canada. pH
measurements were performed potentiometrically and spectroscopically at near-freezing
temperatures. All the bulk new, thin ice and frost flowers showed highly alkaline pH values (>9.0),
which is further supported by the presence of ikaite minerals. Vertical pH profiles from bulk ice cores
revealed a consistent C-shaped pattern during ice growth, with highest pH values (> 9) in both top and
bottom ice sections, and lowest pH (~ 7) in interior ice sections. Brine pH typically remained below that
of the source seawater pH. A conceptual model of pH evolution in the sea ice environment is
proposed, which has major implications for a variety of tropospheric-cryopsheirc processes over polar
oceans.
Page | 501
199
Remote sensing observations of halogen oxides above Polar Regions
1
1
1,2
1,2
3
Anja Schoenhardt , Andreas Richter , Astrid Bracher , Tilman Dinter , Howard Roscoe , Alfonso
4
1
Saiz-Lopez , John P. Burrows
1
2
Institute of Environmental Physics, University of Bremen, Bremen, Germany, Alfred-Wegener3
Institute for Polar and Marine Research, Bremerhaven, Germany, British Antarctic Survey,
4
Cambridge, United Kingdom, Laboratorio de Ciencias de la Atmósfera y el Clima (CIAC), Toledo,
Spain
Reactive halogen species, such as bromine and iodine and their oxides, impact on atmospheric
composition through ozone destruction, changes in the HOx and NOx ratios and in general through
changing the oxidative capacity of the atmosphere. Iodine oxides in particular are capable of forming
atmospheric particles, which may affect the radiation balance. Iodine species therefore are of
importance for climate aspects and interactions, especially as the main source pathways are not fully
identified and might be altered by a changing climate.
Temporal and spatial variations of IO column amounts from long term satellite observations will be
presented. Observations of bromine monoxide, BrO, from satellite are compared to IO to investigate
relations between the two halogen species. Largest abundances of IO are found above the Antarctic
Region. The Weddell Sea for example is an area with apparently active iodine chemistry. Sea ice
cover and phytoplankton concentrations in the surrounding oceans may be related to the source
pathways of iodine species. Comparisons between satellite and ground-based measurements of
halogen oxides complement the analysis.
Page | 502
159
Destruction of tropospheric ozone by activated bromine in synoptic fronts
during Arctic spring
1,2
2
2
1
1
1
Holger Sihler , Thomas Wagner , Steffen Dörner , Udo Frieß , Denis Pöhler , Johannes Zielcke ,
1
Ulrich Platt
1
2
Institute of Environmental Physics, University of Heidelberg, Heidelberg, Germany, Max Planck
Institute for Chemistry, Mainz, Germany
Reactive halogen species are known to play an important role in the destruction of tropospheric ozone.
In the Arctic troposphere, bromine monoxide (BrO) is a key tracer indicating ozone destruction and
satellite observations show that areas affected by significantly elevated BrO concentrations can be
more than a thousand kilometres across. The processes leading to atmospheric bromine activation
are, however, not entirely understood. Furthermore, it is not clear which type of surface (e.g. first-year
sea-ice, frost flowers, or brine) is necessary to activate bromine from its primary source, sea salt, and
able to release it to the overlying atmosphere. Another important question is how BrO is distributed in
the lower troposphere once it is activated. In this study, the measured vertical and horizontal
distribution of BrO in the Arctic troposphere are correlated to meteorology in order to investigate
possible feedback mechanisms with Arctic temperature rise, sea-ice coverage, and tropospheric
ozone in general.
Four years of satellite measurements (GOME-2 on MetOp-A) are used to assess the distribution of
BrO using a newly developed retrieval for the distinct detection of near-surface concentrations in the
Arctic. The satellite data-set is validated and completed by ground-based measurements offering
additional information about the vertical distribution. The comparison between BrO distribution and
ozone sonde as well as weather model data indicates that the distribution of BrO is mainly controlled
by meteorology. In later Arctic spring, peak BrO concentrations are frequently found at the interface
between air-masses of which one is often significantly depleted in ozone. Hence, most of the ozone
destruction occurs in fronts, and, therefore, a change in the Arctic climatology moderated by climate
change will also change the strength of this important sink for tropospheric ozone.
Page | 503
153
Regional ocean and atmospheric modelling of the Caspian Sea - a study of
Caspian Sea ice melt processes and sensitivities
1
1
1
Helen Tamura-Wicks , Ralf Toumi , Paul Budgell
1
Space and Atmospheric Physics Group, Blackett Laboratory, Imperial College London, London,
United Kingdom
We discuss the sensitivities of the Caspian Sea ice to various physical properties through regional
modelling. The Northern Caspian is the southernmost location within the northern hemisphere where
sea ice is found, and is therefore subject to large seasonal variabilities.
An atmospheric (WRF) and ocean (ROMS) model were set up to further explore this sea ice variability.
Model results were compared to satellite observations, allowing for the identification of the main
contributors to the melt processes of Caspian Sea ice and highlight areas of further investigation.
Page | 504
C4.3b - Atmospheric boundary layers in complex terrain and over ice, snow
and vegetated surfaces
10.07.2013 10:15-11:45, Sanada I
975
Examination of turbulence decay and the role of mechanical and buoyant
forcing over a forest during the BLLAST Experiment
1
1
1
2
2
Daniel Alexander , Chaoxun Hang , Eric R. Pardyjak , Marie Lothon , Fabienne Lohou , Soléne
2
3
3
2
Derrien , Olivier de Coster , Henk Pietersen , Eric Pique
1
2
Mechanical Engineering, University of Utah, Salt Lake City, United States, CNRS, Université Paul
3
Sabatier, Lannemezan, France, Meteorology and Air Quality Group, Wageningen University,
Wageningen, Netherlands
The Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) experiment was conducted
from 14 June - 8 July 2011 in Lannemezan, France with the aim of gaining an improved understanding
of various transitory processes associated with the afternoon boundary layer. As part of this
experiment, a tall eddy covariance flux tower was instrumented over a forest dominated by European
Larch trees. Measurements on the tower included incoming and outgoing components of long and
short wave radiation as well as fluxes of sensible heat, moisture momentum, and carbon dioxide at 10
meters above the canopy. At approximately the canopy top, measurements of momentum and
sensible heat fluxes were also made. For this work, we focus on describing the overall decay of
turbulence statistics associated with the transport of heat, momentum, and scalars. In addition, the
effect of the balance between mechanical and buoyant forcing (as a function of distance from top of
canopy) on the decay of turbulence statistics is described and compared to existing work in the
literature. Periods with increased geostrophic forcing are compared to periods dominated by buoyant
forcing. Models using a constant geostrophic forcing are found to more closely match the periods with
strong geostrophic winds suggesting the models are over-predicting the role of mechanical turbulence
production at the transition. Attempts are made using the method proposed by Nadeau et al. (2011) to
quantitatively describe the decay in a manner that captures the two distinct decay regimes observed
throughout the experiment.
Page | 505
681
Analysis of the surface energy budget for the BBLAST 2011 campaign
1
1
2
2
Stefan Wacker , Julian Gröbner , Joachim Reuder , Marius Jonassen
1
2
PMOD/WRC, Davos Dorf, Switzerland, University of Bergen, Bergen, Norway
The Boundary-Layer Late Afternoon and Sunset Turbulence (BBLAST) project aims to investigate the
temporal evolution of the atmospheric boundary layer (ABL). While the growth of the convective
planetary boundary layer (CBL) over land during the day due to solar heating of the Earth´s surface
has been extensively observed and modeled, the early morning transition - when the CBL emerges
from the stable nocturnal boundary layer - and the late afternoon transition (LAT) - when the CBL
decays to a stable stratified boundary layer again - are still difficult to observe and model. Initiated in
2008, the project has gathered about 30 research scientists from the European Union and the United
States to work on this issue. The overall objective of BLLAST is to make more and better observations
of the LAT. Therefore, a comprehensive field experiment was scheduled in France, near the Pyrénées
Mountains. During three weeks in June and July 2011, continuous measurements in the ABL were
performed.
PMOD/WRC deployed an instrumental setup during the field campaign to measure each component of
the radiation budget. The tripod featured two well-calibrated pyranometers and pyrgeometers to
measure the up- and down-welling short-wave and long-wave irradiance. Furthermore, the setup was
equipped with a modified pyrgeometer sensitive in the 8 - 14 µm wavelength range which is used in
conjunction with a traditional pyrgeometer to determine the effective atmospheric boundary layer
temperature. The set-up was placed close to instruments measuring sensible and latent heat fluxes in
order to study the energy budget at the surface. We successfully measured the radiation budget
during the whole campaign and precisely observed the LAT using long-wave measurements. We will
present the analysis of the comprehensive energy budget dataset and the observations of the diurnal
course of the ABL using our long-wave measurements.
Page | 506
1247
Influence of snow on the atmospheric surface layer
1
1
1
2
1,3
Marc Diebold , Holly J. Oldroyd , Hendrik Huwald , Chad W. Higgins , Andreas Christen , Michael
1,4
1
Lehning , Marc B. Parlange
1
School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de
2
Lausanne (EPFL), Lausanne, Switzerland, Department of Biological and Ecological Engineering,
3
Oregon State University, Corvallis, United States, Department of Geography, University of British
4
Columbia, Vancouver, Canada, WSL Institute for Snow and Avalanche Research SLF, Davos,
Switzerland
Recent field campaigns held at the Val Ferret watershed in 2012 provided turbulent measurements in
the atmospheric surface layer with and without snow cover. The turbulent kinetic energy (TKE) over
the snow was reduced in comparison to the measurements obtained over bare surface. The
“smoothing” of the surface by snow probably has a small role to play in the decrease of the TKE but
the importance of the snow cover itself still has to be determined. Recent measurements obtained
during the Plaine Morte 2013 field campaign using sonic anemometers are analysed. We discuss how
the snowpack impacts the atmospheric turbulence under various snowpack conditions.
Page | 507
1144
Snow transport in the turbulent boundary layer
1,2
2
2
2
1,2
Christine Groot Zwaaftink , Gian Lieberherr , Jan Overney , Marc Diebold , Katherine Leonard ,
1
2
1,2
Stefan Horender , Marc Parlange , Michael Lehning
1
2
WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland, School of Architecture,
Civil and Environmental Engineering, EPFL, Lausanne, Switzerland
Drifting snow highly influences the alpine snow cover. Although observations and measurements show
that this boundary layer process is highly intermittent, simulations of snow transport thus far rely on
mean flow fields and steady-state assumptions. Such simulations are able to roughly represent the
snow cover on time scales of several days up to a season, and on spatial scales of several meters.
However, to represent the snow distribution on small spatial and time scales, averaging in time and
space has obvious limitations.
In this study we develop a Lagrangian stochastic model for snow transport. Wind field data are
generated separately by a state of the art large eddy simulation. Saltation and suspension are not
artificially separated in this model but the turbulent flow directly acts on the particles. The resulting
trajectories of particles have then characteristics of typical ballistic saltation or - mainly for smaller
sizes - of suspended particles that follow the wind field. Particles can start saltation by aerodynamic
entrainment, rebound and ejection/splash. We will examine how these processes affect the small
scale snow distribution and lead to mass flux intermittency.
Model results show that the domain-averaged concentration of suspended snow starts to fluctuate
around an equilibrium state a few seconds after drift initiation. The establishment of an equilibrium
state agrees with previous studies. However, model results suggest that mass transport may remain
intermittent locally. Intermittent fluctuations in snow transport are also observed in field and wind
tunnel experiments and are larger than in the model. The larger intermittency can be explained by
variations in snow conditions and snow availability. These effects, however, are hard to distinguish in
measurements. This Lagrangian snow transport model could in future be used to give more insight in
the origin of such fluctuations and the influence of turbulence on snow transport.
Page | 508
1271
An observational Arctic Flux Network supporting the international arctic
systems for observing the atmosphere and global cryosphere watch
1
2
3
2
1
Taneil Uttal , Andrey Grachev , Irina Repina , Ola Persson , Jeffrey Key
1
2
NOAA Earth Systems Research Laboratory, Boulder, United States, University of Colorado
3
Cooperative Institute for Research in the Environmental Sciences, Boulder, United States, Russian
Academy of Sciences Obukhov Institute of Atmospheric Physics, Moscow, Russian Federation
In recent years a number of Arctic stations have installed micro-meteorological towers in recognition of
the need to explicitly quantify the detailed exchanges between the surface and the atmosphere. These
towers are typically equipped with temperature, humidity and wind sensors at several levels (allowing
the calculation of turbulent heat fluxes and fine scale characterization of the near-surface boundary
layer) and often also have accompanying measurements of incoming and outgoing solar radiation
(allowing energy balance closure), CO2 and methane sensors (allowing calculation of gas fluxes) and
ancillary measurements of snow depth and permafrost active layer temperature profiles.
Preliminary results are presented and compared for Eureka /Alert (Canada) and Tiksi (Russia) that
document the wide variation in seasonal and regionally influences on the characteristics of the
atmosphere-surface exchanges at the 3 sites.
A developing concept is presented for developing an Arctic Flux Network with standardized
measurement and data protocols that will support future inter-observatory science between the
member observatories of the International Arctic Systems for Observing the Atmosphere (IASOA). The
IASOA Network is currently coordinating with the Global Cryosphere Network (GCW) program provide
the atmospheric measurements that are most critical for development of an observational CryoNET to
study the atmosphere-surface process exchanges as an integrated system.
Page | 509
B4.1f - Global monsoon system: past, present and future
10.07.2013 10:15-11:45, Aspen I
573
Achievements and research challenges of the African Monsoon
Multidisciplinary Analysis (AMMA) initiative
1
2
3
4
Andreas Fink , Douglas J. Parker , Serge Janicot , Christopher D. Thorncroft
1
2
3
University of Cologne, Cologne, Germany, University of Leeds, Leeds, United Kingdom, Université
4
Pierre et Marie Curie, Paris, France, State University of New York Albany, Albany, United States
Research within the first phase of AMMA (2002-2010) achieved several novel findings on the
dynamics of the West African Monsoon (WAM). On the mesoscale, the role of soil moisture gradients
on length scales between 10- and 40 km in triggering organised mesoscale convective systems (MCS)
in the Sahel has been demonstrated. Moreover, convection tends to develop predominantly over drier
soils in this region. Further, night-time low-level jets develop in the boundary layer that are important
(a) for the genesis of an extensive night-time to early-morning stratus in the southern moist WAM zone
and (b) the northward push of moisture towards the northern Sahel/southern Sahara. Simulations
within the AMMA-related UK Cascade project suggest that convection-resolving simulations and
thereby the simulations of density currents are necessary to remove biases in, for example, the diurnal
cycle of convection in the Sahel.
On the synoptic scale, AMMA research has confirmed the role of MCSs in the triggering and growth of
African Easterly Waves (AEWs) across the continent. The role of AEWs in tropical cyclogenesis at
least off the West African coast has been re-affirmed. AMMA research has also shed light on modes of
intraseasonal variability, some of which are related to (partly extratropically) forced variations in the
West African Heat Low (WAHL). On interannual time scales, it has been found that the role of
anomalies in sea-surface temperatures in the tropical equatorial Atlantic has changed with a decadal
change in the background climatic state: Before (after) about 1979, a dipole (monopole) rainfall
anomaly was induced over the WAM region.
Several grand research challenges that remain will be highlighted. In its second phase from 2010 to
2020, AMMA is acting to coordinate research in these and other areas, working in partnership with
new research programmes which have been funded in various countries.
Page | 510
453
Abrupt weakening of the Eurasian and North African summer monsoons in the
1960s and links to extratropical North Atlantic cooling
1
1
John Chiang , Yuwei Liu
1
University of California, Berkeley, United States
Previous modeling and paleoclimate studies have suggested that cooling originating from extratropical
North Atlantic can abruptly weaken the Eurasian and North African monsoons. The climatic signature
includes a widespread cooling over the Eurasian and North African continents, and associated
increase to surface pressure. Motivated by these studies, we explore (i) whether such co-ordinated
changes are similarly exhibited in the observed 20th century climate; and (ii) potential atmospheric
teleconnection mechanisms.
Our analysis of observational and AMIP-type GCM simulations suggest that such co-ordinated
changes did in fact occur in the late 1960´s. We objectively extracted a leading mode of surface
temperature, sea level pressure and precipitation changes that exhibit a monotonic shift in the 1960's,
and with a spatial pattern resembling the climate signature seen in modeling studies of North Atlantic
cooling. A similar objective analysis of atmospheric general circulation model (AGCM) simulations
forced by 20th century observed SST shows similar results, suggesting that origins of the climate shift
reside in the SST, in particular over extratropical North Atlantic.
We also investigated atmospheric teleconnection mechanisms in AGCM simulations of extratropical
North Atlantic cooling, under the hypothesis that its influence is communicated to the monsoons
through atmospheric temperature. A radiative feedback analysis shows that positive cloud and water
vapor feedbacks amplify the cooling over North Africa and Eurasia, helping to communicate the signal.
A moisture budget analysis of the North African summer rainfall response suggests that the 'direct
moisture effect' (reduced humidity in response to the cooling) partly drives the weakened rainfall
response. Taken together, they suggest that atmospheric temperature is a plausible mechanism to link
extratropical North Atlantic with the North African summer monsoonal rainfall weakening.
Page | 511
668
The South American monsoon: characteristics and variability
1
Alice Grimm
1
Physics, Federal University of Parana, Curitiba, Brazil
The warm season in South America shows features typical of a monsoon climate, even though the
seasonal reversal of the surface wind is not apparent. If the annual mean is removed, though, the
surface wind does reverse in association with the strong diabatic heating in the subtropical highlands.
Besides, the seasonal cycle of precipitation over most of South America is monsoon-like, with great
contrast between the winter and the summer precipitation over most of the continent. The monsoon
regime even extends to the subtropics.
Therefore, an increased understanding of the South American Monsoon system (SAMS) and the
ability to forecast its variability is important in many ways, since the monsoon variability affects
significantly the hydroelectricity generation and the agriculture, which are crucial components of local
economies. Characteristics, functioning and variability of the SAMS are reviewed, with special
emphasis on the monsoon variability in intraseasonal, interannual and interdecadal time scales and its
impact on the frequency of extreme precipitation events.
In intraseasonal time scale, the impact of the Madden-Julian Oscillation on the monsoon precipitation
and its extreme events is assessed with unprecedented temporal and spatial coverage, and some
mechanisms of this impact are discussed. In the interannual time scale, the ENSO impact and the
tendency to reversal of precipitation anomalies in central-east South America from spring to summer,
possibly related to regional surface-atmosphere interactions, are broached. Interdecadal modes of
monsoon precipitation variability are shown and some connections between global SST interdecadal
variability and monsoon precipitation are established. Examples of the possible remote influences of
SAMS-related anomalous heat sources (associated with convection anomalies) are presented.
Acknowledgments. This work was supported by the Brazilian National Council for Scientific and
Technological Development (CNPq).
Page | 512
A4.3a - High Latitude Climate Change and Links with the Cryosphere
10.07.2013 13:15-14:45, Sanada II
851
Arctic amplification evaluated from the JRA-55 re-analysis data
1
1
1,2
1
3
Meiji Honda , Jinro Ukita , Katsushi Iwamoto , Mio Kadono , Yusuke Harada
1
2
3
Niigata University, Niigata, Japan, National Institute of Polar Research, Tachikawa, Japan, Nagoya
University, Nagoya, Japan
In recent decades the near-surface air temperatures in the Arctic have risen much faster than the
global average, known as Arctic amplification. Previous studies have investigated its underlying
processes, especially focusing on the roles of ice-albedo feedback and the heat transport from midlatitudes. However, there is no clear-cut answer as regarding their relative importance to the current
rapid warming in the Arctic. There are many difficulties. A data issue clearly exists. The results
regarding temperature trends vary among different reanalysis products, not to mention different
seasons, altitudes, and analysis periods all contribute to variations. Instead of temperatures we focus
on the northward heat transport to the Arctic region, one fundamental factor that can contribute to the
Arctic warming. Previous work based the ERA-Interim reanalysis data indicates that the wintertime
northward heat transport in the Arctic (60˚N-90˚N) increased during the period of 1979-2010 due
mainly to changes in large-scale circulation (Harada, 2012). In this presentation we show preliminary
results from a similar calculation based on the JRA-55 re-analysis data, making a comparison on
trends and variability in the northward heat transport in the Arctic between two most up-to-dated
reanalysis products.
Page | 513
496
Roles of natural and anthropogenic climate change and variability in Greenland
climate over the industrial and future periods using CCSM3
1
1
Heather Andres , W. R. Peltier
1
Physics, University of Toronto, Toronto, Canada
Paleoclimate records indicate that both the Greenland Ice Sheet and the West Antarctic Ice Sheet
1
were considerably reduced in the past under similar climatic conditions to today . Nevertheless, it
remains difficult to predict how these ice sheets will respond to increasing greenhouse gas
concentrations and anticipated reductions in atmospheric aerosols. A central impediment to such
predictability concerns the inadequacy of our understanding of the contribution of natural climate
variability to the mass balance of the Greenland Ice Sheet. We have employed a suite of millenniumtimescale, global, atmosphere-ocean general circulation simulations to identify robust connections
between Greenland climate and natural sources of external variability, including solar and volcanic
sources, as well as internal regional sources of variability. In our presentation, we will apply the results
of this analysis to a suite of simulations for the industrial period and two future periods generated with
different representative concentration pathways.
The results of these analyses have allowed us to disentangle the respective roles of natural and
anthropogenic climate variability in generating surface climate change over Greenland. A primary goal
is to identify the time beyond which the anthropogenic influence becomes unambiguously evident
against the background of natural variability, both in an ensemble average sense and in each
simulation individually. We focus especially on the latter case, as it is most comparable for
understanding the historical record. Finally, we will examine the role that natural climate variability has
played in delaying the onset of noticeable climate change in Greenland until the mid-1990´s by
focussing upon a simulation that exhibits similar features.
1. Tripati, A.K., C.D. Roberts and R.A. Eagle (2009) Science 326(5958):1394-1397
Page | 514
658
Cyclone activities and associated accumulation/temperature changes over the
Greenland Ice Sheet
1
2
3
Linling Chen , Ola M. Johannessen , Erlend Moster Knudsen
1
2
Nansen Environmental and Remote Sensing Center, Bergen, Norway, Nansen Scientific Society,
3
Bergen, Norway, Geophysical institute, University of Bergen, Bergen, Norway
Current assessments of the Arctic climate in the near-term future predict continuous change in the
cryosphere, notably the accelerating melt of the Greenland Ice Sheet (GrIS). However, the mechanism
leading the changes of accumulation/temperature over the GrIS is poorly understood. Greenland, with
its steep coastal mountains, plays an important role on the dynamics of the cyclone activities. This
issue has already been addressed by many previous studies, but the influence of cyclone activities on
the moisture/heat transport to the plateau are not clearly known yet. Therefore, to study the cyclone
activities in this region will give better understanding of the atmospheric impact on the mass changes
of the GrIS. In our study, ERA-interim reanalysis data (since 1979) is used to investigate the cyclone
activities around Greenland area and the associated variations of accumulation and temperature over
the GrIS. Results indicated that the changes of accumulation/temperature over the GrIS can be
explained by the cyclone activities in Baffin Bay and Danmark Strait. Thus, it indicated the impact of
cyclones on the Surface Mass Balance of the GrIS during recent 30 years.
Page | 515
504
Continental heat anomalies and extreme melting of the Greenland ice surface
in 2012 and 1889
1
1
2
2
William Neff , F. Martin Ralph , Matthew Shupe , Gilbert Compo
1
2
Physical Sciences Division, NOAA/ESRL, Boulder, United States, Cooperative Institute for Research
in the Environmental Sciences, University of Colorado at Boulder, Boulder, United States
The summer of 2012 saw three major warmings at Summit Station on the Greenland ice sheet; two of
these events were associated with melting of the entire ice surface on 11 July and partially on 29 July
as documented by satellite imaging. These warmings coincided with a major summer heat anomaly
over the North American continent. Isentropic back-trajectory analysis showed the probable origin of
air arriving at Summit station on 11 July to be from the mid- and southeastern U.S. We also found
significant distortions of the polar vortex that led to the creation of Atmospheric Rivers, narrow
filaments of high moisture air, over the western Atlantic just prior to the events on 11 and 29 July that
coincided with air trajectories arriving at Summit a few days later. One of these in early July
transported warm moist air first over Greenland and the proceeded to produce heavy rain in the
southern UK and northern France on 12 July. Because the most recent event of such a scale over
Greenland last occurred in the 1889 as documented in ice core and radio sounding analyses, we
examined the synoptic environment in the summer of 1889 using the Twentieth Century Reanalysis
which uses only historic global surface pressure measurements and sea-surface temperatures
beginning in 1871. We found very similar conditions; namely, heat anomalies over the North American
Continent in the summer of 1889, distortions of the polar vortex and the formation of Atmospheric
Rivers leading to moisture increases over the Greenland ice sheet. Given the complex interaction
between potential trends in continental heating, changes in the strength of the polar vortex, and
increasing moisture in the atmosphere, we explore the implications from comparing these two widely
separated events for future changes over Greenland.
Page | 516
1284
The evaluation of Arctic reanalyses and climate models using downwelling
longwave fluxes at Summit Station, Greenland
1
1
2
2
2
Christopher J Cox , Von P. Walden , Matthew D. Shupe , Gilbert P. Compo , Gijs de Boer , Konrad
3
Steffen
1
2
University of Idaho, Moscow, Idaho, United States, CIRES, Univ. of Colorado, NOAA/ESRL,
3
Moscow, Idaho, United States, Swiss Federal Institute for Snow and Landscape Research, Zürich,
Switzerland
Recent studies have shown that the downwelling longwave flux (DLW) is an important parameter in
the Arctic surface energy budget. Changes in the DLW play an important role in sea ice melting over
the Arctic Ocean and in surface melting over the Greenland Ice Sheet (GIS). Ground-based
observations provide the most accurate estimates of the DLW, but the network of observations is
sparse and records are short, so it is necessary to include estimates of DLW from gridded data sets,
such as reanalyses, for a more comprehensive analysis. Thus, it is important to conduct studies
evaluating both the performance of the reanalyses and the complexities involved in comparing gridded
data to point observations. Two independent measurements of the DLW from ground-based
observations are available at Summit Station, Greenland with an overlap period from July 2010
through August 2012; one from a Broadband Surface Radiation Network station and another derived
from spectral radiances obtained by an infrared spectrometer that is part of the Integrated
Characterization of Energy, Clouds, Atmospheric state and Precipitation at Summit (ICECAPS)
observatory. The availability of these measurements, the homogeneity of the central GIS surface, and
the relatively large distance from data assimilation locations make Summit Station an ideal location for
conducting reanalysis evaluations. In this study, we use a time-frequency signal decomposition
technique (e.g., wavelet analysis) to evaluate reanalysis estimates of DLW at temporal scales ranging
from three hours through the annual cycle. First, we evaluate the ground-based observations of DLW
at Summit Station to set context for our ability to measure this parameter. Then we use the groundbased observations to evaluate the performance of the reanalysis products and to gain insight into
comparisons between point measurements and gridded data sets. Finally, we extend this analysis to
compare the measured datasets with future projections using CMIP5 modeled fluxes.
Page | 517
268
Comparison of weather in the Kaffiøra region (Svalbard) in summer seasons of
2010 and 2011 with long-term conditions
1
1
Rajmund Przybylak , Andrzej Arazny
1
Department of Meteorology and Climatology, Nicolaus Copernicus University, Torun, Poland
In this paper the meteorological conditions in the Kaffiøyra region (Svalbard) in summer seasons of
2010 and 2011, are described and compared with long-term conditions (19 seasons between years
1975 and 2011) existing in the area. The analysis concerned two diametrically opposite natural
environments: non-glaciated in the case of the Base Station (KH), and glaciated, as represented by
sites located on the Waldemar Glacier (LW2) and immediately at its front (LW1).
Weather in summer seasons of 2010 and 2011, compared with the long-term average conditions,
were characterised by notably greater values of wind speed, slightly lesser cloudiness, longer
sunshine duration and considerable dryness of the air, also evident in the very small precipitation
-1
amounts. The year 2010 was particularly extreme with its highest average wind speed (5.8 ms ), and
the smallest precipitation (only 8.5 mm), compared with the other 18 periods of observation. It was
also the second coldest summer season. The summer of 2011 was apparently warmer than the
o
o
previous one (by 1.6 C on average) and the long-term standard (by 0.9 C). However, the other
meteorological elements displayed similar characteristics as in the summer of 2010.
For Waldemar Glacier long-term data exist only for two main variables, i.e. the air temperature and
precipitation. The summer of 2010 was much colder than average. Thermal anomalies at two
o
observation sites, LW1 and LW2, reached -0.7 and -1.3 C, respectively. On the other hand, the air on
the Waldemar Glacier was much warmer in 2011 than the average. Positive thermal anomalies at the
o
above-mentioned sites were 1.4 and 1.2 C, respectively.
In the summer season of 2010, at the Waldemar Glacier the precipitation was half the long-term total.
In the summer season of 2011, precipitation remained below the long-term average, but its negative
anomalies were not great, especially in the case of the LW2 site.
Page | 518
A5.4c - Asian glaciers and climate change
10.07.2013 13:15-14:45, Aspen II
358
Sensitivity of runoff from a Himalayan debris-covered glacier
1
1
Koji Fujita , Akiko Sakai
1
Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
Despite well investigated processes how debris-mantle alters melt of glacier ice, mass balance, runoff
and response to climate change of Himalayan debris-covered glaciers are not well understood. Many
previous studies dealt with the ice melting under debris mantle by conventionally multiplying some
parameters obtained by field experiments while other studies calculating detailed heat conduction
through debris layer were unable to be applied to catchment scale because of immeasurable
heterogeneous debris distribution. Here we establish a runoff model for Himalayan debris-covered
glaciers in which distribution of debris thermal property is estimated from multi-temporal ASTER data.
We validated the model for a basin consisting of Tsho Rolpa Glacial Lake - Trambau Glacier in the
Nepal Himalaya at which a hydro-meteorological observation has been conducted in the 1990s. We
calculated long-term averages of runoff components for the period 1980-2007 using reanalysis
gridded datasets (NCEP and Aphrodite). Our calculation suggests that debris over the Trambau
Glacier significantly enhances ice melting and adds excess water to total runoff. Uncertainties due to
estimations of thermal property and albedo of debris-covered surface are evaluated to be about 6% of
runoff from debris covered area. We evaluated sensitivities of runoff components to changes in air
temperature and precipitation. Temperature warming simply increases the total runoff by increased ice
melt whereas increase of precipitation reduces the total runoff in which ice melting is suppressed by
snow cover having high albedo. Response of total runoff to changing precipitation is so complex
because individual components (glacier, debris and ice-free terrain) respond in different manners.
Considering inter-annual variability, impact of air temperature is ten times greater than that of
precipitation.
Page | 519
905
Glacier mass balance modeling in high mountain Asia: a case study from the
Langtang catchment in Nepal
1
1
1,2
1
Silvan Ragettli , Martin Heynen , Walter W. Immerzeel , Francesca Pellicciotti
1
2
ETH Zürich, Zürich, Switzerland, Utrecht University, Utrecht, Netherlands
Understanding the response of glaciers in the Himalaya to a changing climate requires appropriate
models that consider all important glacier processes. If a model is based on physical principles and
mass- and energy balances are closed, the model does not have to be calibrated, but requires
detailed meteorological input which is usually not available for remote Himalayan catchments. On the
other hand, if glacier processes are parameterized, the model requires less input data but the risk of a
compensation of errors through different model components increases, as does data demand for
model calibration.
In this study, we apply an energy balance (EB) model and the physically-oriented glacio-hydrological
model TOPKAPI-ETH to simulate annual glacier mass balances in the Langtang catchment in Nepal.
One of the most important characteristics of the study area is that many glaciers are extensively debris
covered. Another important characteristic of the area is the steep topographic relief which favors the
accumulation of snow on glaciers by avalanches. The two models ability to simulate the relevant
glacier processes is tested against a unique set of meteorological data and measurements of surface
ablation at the snout of Lirung and Yala glacier. Measurements of debris thicknesses and snow depth
constrain the initial conditions and provide a detailed description of glacier characteristics.
The detailed information from the field experiment allowed the EB-model to reproduce observed
glacier melt without further calibration. The insights about glacier processes from the field experiment
and glacier mass balances provided by the application of the EB-model helped to constrain
parameters of the less physically-based model TOPKAPI-ETH, which could then be used to simulate
glacier mass balances and runoff of the entire catchment and explain the spatial variability of mass
balance over the different glaciers.
Page | 520
300
Glacier mass change 2003-2009 in the Hindu Kush - Karakoram - Himalaya
1
2
1
3
4
Andreas Kääb , Etienne Berthier , Chris Nuth , Julie Gardelle , Yves Arnaud
1
2
Department of Geosciences, University of Oslo, Oslo, Norway, LEGOS, CNRS, Toulouse, France,
3
4
LGGE, CNRS, Grenoble, France, LTHE/LGGE, IRD, Grenoble, France
In the Hindu Kush - Karakoram - Himalaya region (HKKH), a paucity of appropriate glacier data has
prevented a comprehensive assessment of current regional mass balance. However, there are indirect
evidences of a complex pattern of glacial responses in reaction to heterogeneous climate change
signals. Here, we provide the first coherent data set of detailed glacier thickness changes over the
HKKH during 2003-2009 by combining ICESat laser altimetry, Landsat multispectral imagery, and the
SRTM elevation model. In the eastern, central and south-western parts of the HKKH, glacier wastage
is widespread with regional thinning rates up to 0.66 ± 0.09 m/yr in the Jammu-Kashmir region.
Conversely, in the Karakoram, glaciers are close to balance with only a slight thinning of 0.07 ± 0.04
m/yr. Regionally averaged thinning rates under debris-mantled ice are similar to those of clean ice
despite insulation by debris covers. That debris-covered ice thins at a similar rate as exposed ice
shows that the role of debris mantles in glacier mass balance must be reassessed. The 2003-2008
specific mass balance for our entire HKKH study region is -0.21 ± 0.05 m/yr water equivalent (WE),
significantly less negative than the global average of ca. -0.7 m/yr WE for glaciers and ice caps. This
difference is mainly an effect of the balanced glacier mass budget in the Karakoram. The
corresponding HKKH sea level contribution is +0.035 ± 0.009 mm/yr amounting to 1% of the presentday sea level rise. For the mountain catchments of the Indus and Ganges basins, the glacier
imbalance contributes ca. 3.5% and ca. 2.0%, respectively, to the annual average river discharge, and
up to ca. 10% for the Upper Indus basin.
Page | 521
1262
Climatic variation and runoff from glacierised Himalayan basins
1
1
1
David Collins , Joshua Davenport , Ryan Wilson
1
School of Environment & Life Sciences, University of Salford, Manchester, United Kingdom
Precipitation and runoff usually increase with elevation in high mountains but Himalayan tributaries of
both Indus and Ganges often rise in relatively dry interior areas and flow is modified downstream in
areas receiving winter snowfall and summer monsoon snow and rain. Tributary contributions to the
major rivers, the upper Indus, Jhelum, Sutlej and Ganges therefore respond to differing climatic
signals, which also affect glacier mass. Long-term measurements of discharge upstream of large
dams are available for the Jhelum and Sutlej since the 1920s, but show differing patterns of variation.
Whereas discharge in the Jhelum declined to the 1960s before recovering, flow in the Sutlej continued
to decline. Highly glacierised areas south-east of Nanga Parbat receive considerable amounts of
precipitation distributed throughout the year but other Jhelum and also Sutlej headwaters are summer
monsoon dominated. Precipitation measurements exist for dry areas of the upper Indus basin since
the early 1900s, but other measurements in the Kaghan valley and upstream of the Mangla dam only
start in the 1960s. Correlation between year-to-year variations in precipitation across these headwater
regions and between precipitation and runoff in headwater and main-stem basins suggest that runoff
declines with summer snowfall on glaciers in areas of the Upper Indus where valley bottoms at
elevations below glaciers are dry, but runoff increases with summer precipitation south of the main
Himalaya range. Differences arise therefore in water resource availability from year to year and
through time in the various basins downstream.
Page | 522
A2.2b - Coupling processes with hydrosphere (ocean) and cryosphere
10.07.2013 13:15-14:45, Forum
1196
Antarctic sea ice trends, stratospheric ozone, and internal climate variability
1
1
Lorenzo Polvani , Karen Smith
1
Columbia University, New York, United States
The observed positive trends in Antarctic sea ice pose a challenge to our understanding of the climate
system, in that one would expect sea ice to melt in a warming climate, as the Arctic shows. In addition,
models participating in the Coupled Model Intercomparison Project (CMIP) Phases 3 and 5 are unable
to simulate the observed positive trends. Recent single-forcing experiments where only stratospheric
ozone is changed, show that ozone depletion causes negative sea ice trends and, conversely, that
ozone recovery will mitigate the future sea ice loss associated with increasing greenhouse gases.
Hence, over the observational period, models indicate that both greenhouses gases and ozone
depletion would act in the same direction, and produce negative sea ice trends. However,
investigation of trends in CMIP5 pre-industrial control model integrations reveal that both positive and
negative trends, with amplitudes much larger than the one in the observational record, can occur in the
absence of a forcing agent, solely as a consequence of internal climate variability. This suggests that
the recently observed trends may be a reflection of such variability rather than a mere response to
anthropogenic forcings.
Page | 523
507
Close interactions between the Antarctic cyclone budget, large-scale
atmospheric circulation and sea ice
1
2
3
Petteri Uotila , Timo Vihma , Masha Tsukernik
1
2
CSIRO Marine and Atmospheric Research, Aspendale, Australia, Finnish Meteorological Institute,
3
Helsinki, Finland, Environmental Change Initiative, Brown University, Providence, United States
The Antarctic climate system includes components, such as the mass balance of the Antarctic ice
sheet, the sea-ice extent, and the heat and freshwater budgets of the Southern Ocean, which are
quantitatively poorly known. Common to these three processes is that they all are strongly affected by
the wind field. The essential link between the large-scale atmospheric circulation and wind is provided
by cyclones which strongly affect the wind field and interact with the large-scale circulation.
We aim to better understand interactions between large-scale atmospheric circulation, cyclones and
sea-ice in the Southern Ocean by applying novel methods and using the best available remote
sensing and reanalyses products. For the first time, we quantify the relationship between the Antarctic
high-frequency atmospheric signal, represented by cyclones, and large-scale atmospheric variability.
Based on the ERA-Interim 1979-2011, we identify cyclones and calculate monthly regional cyclone
budgets as cyclogenesis minus cyclolysis plus net movement of cyclones into regions of the Southern
Ocean. Moreover, we demonstrate how cyclones affect the sea-ice dynamics, including the position of
the sea-ice edge, and associate cyclone budgets with major atmospheric circulation modes: the
Southern Annular Mode (SAM), the El Nino-Southern Oscillation (ENSO), the Zonal Wave 3 Pattern
(ZW3) and the Semi-Annual Oscillation (SAO).
The SAM index has a strong connection with cyclone budgets across all regions. Positive SAM values
are related to increased southward movement of cyclones, resulting in higher cyclone densities along
the Antarctic coast. The ENSO index shows strong associations with the cyclone behaviour in the
Amundsen-Ross Seas, whereas other regions are less sensitive to it. The ZW3 index has a stronger
association with the meridional movement of cyclones than other indices. Associations between the
cyclone budget and SAO are weaker. Our analysis shows the interdependence between cyclones and
large-scale circulation in moderating the Antarctic climate.
Page | 524
584
The atmospheric response to sea ice loss in an aquaplanet AGCM
1
1
1
Caroline Ely , Tim J. Woollings , David J. Brayshaw
1
Department of Meteorology, University of Reading, Reading, United Kingdom
Arctic sea ice loss is a robust feature of observations and of climate model projections, yet possible
mechanisms by which this may influence the atmospheric circulation remain unclear. Naturally, these
two components are highly coupled with each other and with the ocean, but there is much merit in
breaking into the coupled system to improve our understanding of the mechanisms involved. Here, we
focus on the extent to which sea ice anomalies may affect the midlatitude circulation, in particular
features such as the jet stream and storm tracks.
Results will be presented from experiments in an aquaplanet, atmosphere-only, zonally symmetric
configuration of HadGAM6.1. An ice cap of realistic latitudinal extent is enforced over a selection of
fixed SST patterns. The outcome from this simple setup enables investigation of dynamical processes
whereby the sea ice anomaly moderates the midlatitude circulation, and how this response may be
dependent on the background atmospheric state (as determined by the SST pattern).
The situation in reality is complicated by zonally asymmetric forcings at the lower boundary, such as
orography and SSTs. These aquaplanet model runs will inform a suite of experiments in which
representative zonally asymmetric features are added to the lower boundary conditions before
imposition of sea ice anomalies.
Page | 525
51
Potential importance of midlatitude oceanic frontal latitude on the atmospheric
annular mode variability as revealed from aqua-planet experiments
1
1
1
1
2
Fumiaki Ogawa , Hisashi Nakamura , Kazuaki Nishii , Takafumi Miyasaka , Akira Kuwano-Yoshida
1
2
RCAST, University of Tokyo, Tokyo, Japan, ESC, Jamstec, Yokohama, Japan
The annular mode variability in the extratropical atmosphere is manifested as latitudinal displacement
of an eddy-driven polar front jet (PFJ) and an associated stormtrack. Recent observational and
modeling studies indicate PFJ in climatological-mean state forms in the vicinity of a midlatitude
oceanic front that maintains a surface baroclinic zone by countering poleward eddy heat transport. The
present study reveals strong sensitivity of the meridional structure of the annular mode to the latitude
of an oceanic front, through a set of “aqua-planet” experiments with an atmospheric general circulation
model with zonally uniform sea-surface temperature (SST) prescribed at the model lower boundary
with frontal SST gradient whose latitude varies from one experiment to another. The simulated lowfrequency variability in each of the experiments represents meridional displacement of PFJ with a high
degree of zonal symmetry, as observed in the Southern Annular Mode (SAM). The nodal latitude of
westerly anomalies associated with the annular mode tends to shift together with the front. The
positive phase of the model annular mode is characterized by eddy-driven PFJ situated poleward of
the SST front, and its axis shows unambiguous sensitivity to the frontal latitude. In the negative phase,
by contrast, PFJ form near 40° latitude insensitively to the latitude of the SST front in any of the
experiments. The particular latitude nearly corresponds to the climatological-mean PFJ axis that is
realized in an experiment where the midlatitude frontal SST gradient is smoothed out and therefore
atmospheric internal dynamics through eddy-mean flow interactions dominates over thermodynamic
effects by the underlying SST. The results suggest that the annular mode may be interpreted as a
manifestation of low-frequency shifts of the atmospheric general circulation between a dynamical
regime dominated by the thermodynamic influence of frontal SST gradient and that by atmospheric
internal dynamics.
Page | 526
C2.1b - Dynamics and impact of ice formation in clouds
10.07.2013 13:15-14:45, Studio
786
Cirrus ice water content, crystal number and size: new statistical analysis from
several field campaigns
1
2
1
1
3
3
Martina Krämer , Anna Luebke , Jessica Meyer , Christian Rolf , James Dorsey , Martin Gallagher ,
2
Linnea Avallone
1
2
IEK-7, Forschungszentrum Juelich, Jülich, Germany, LASP, University of Colorado at Boulder,
3
Boulder, United States, SEAES, University of Manchester, Manchester, United Kingdom
Cirrus clouds, only occuring at altitudes higher than about five kilometers, are known to be important
contributors to the Earth´s radiation budget. However, describing their microphysical properties
remains challenging. On the one hand, this is due to the rare opportunities for in-situ measurements
on high altitude aircraft, and on the other hand by the difficulties associated with obtaining reliable
measurements at fast aircraft speeds.
Here, we present probability distribution functions of ice water content, ice crystal number and mean
mass size compiled from the most comprehensive available cirrus data set sampled during 15 field
campaigns. The cirrus data base encompasses the latitude range from -20 deg South to 67 deg North,
the altitude range from 5 to 20 km, the temperature range 182 - 240 K, and represents ~60 hours of
cloud sampling, i.e ~43200 of flight kilometers -about the circumference of the earth.
The measurements were performed with the total water hygrometers FISH and CLH as well as the
cloud particle spectrometers FSSP-300/100 (0.6-20/30 micron diameter), NIXE-CAPS and 2-DS
(0.6/10 - 1000 micron diameter). Before interpreting the microphysical meaning of the frequency
distributions, we investigate possible instrument influences -such as ice crystal shattering, electronic
noise or particle sampling range, etc.- on the results.
A main finding of this study is that the ice water content frequency distributions are bimodal, as are the
distributions of the ice crystal numbers. This implies that two types of cirrus exist -thin and thick- and
that the crystal numbers might have an important influence on the ice water content. An additional
observation is that in most of the campaigns ice water content and ice crystal numbers of both cirrus
types increase with temperature. An exception is the MACPEX campaign 2011 out of Houston, USA,
where this relation is inversed.
Page | 527
386
Aircraft observations of the initiation and development of ice in tropical clouds
1
1
1
Paul Lawson , Sarah Woods , Sara Lance
1
SPEC inc, Boulder, United States
More than 50% of the Earth's precipitation originates in the ice phase. The focus of the Ice in Clouds
Experiment - Tropical (ICE-T) project was to make airborne observations of ambient aerosols and
initiation/development of ice in Tropical cumulus clouds. Two aircraft were involved, a C-130 operated
by NCAR, and a Learjet operated by SPEC, Incorporated. This presentation focuses on airborne
measurements of the very early detection and continued development of ice in strong (10 to 15 m/s)
updrafts. Cloud bases were consistently observed within the temperature range from +20 to +23 C and
millimeter-diameter drops were routinely observed at the 0 C level. In general, clouds with strong
updrafts were either ice-free or were just beginning to develop small (30 to 100 micron) ice at about
the -8 C level. The ice was distinguished from small cloud drops using (2.3 micron pixel) imagery from
the CPI component of a 3V-CPI probe. Ice grows at about 1 micron per second in these watersaturated clouds, so frozen drops rapidly become non-spherical. When small ice was seen in strong
updrafts at - 8 C, none of the millimeter-diameter drops observed on the (10-micron pixel) 2D-S
imagery were observed to be frozen (i.e., non-spherical). However, upon aircraft penetration of the
same updraft three minutes later at -12 C, all of the millimeter drops were observed to be frozen, and
the only supercooled drops that remained were those with diameters < 500 microns. While some of
the frozen millimeter drops show evidence of spicules, the rapid cloud glaciation is outside the HallettMossop ice multiplication temperature range. This presentation shows examples of the aircraft
measurements and also results of early modeling work that is currently being conducted to see what
roles primary nucleation, sedimentation and ice multiplication play in the rapid glaciation of cloud.
Page | 528
715
Ice nucleation and dehydration in the tropical tropopause layer
1
2
1
Bruce Gandrud , Eric Jensen , Paul Lawson
1
2
SPEC Inc., Boulder, United States, NASA Ames Research Center, Moffett Field, United States
Optically thin cirrus in the Tropical Tropopause Layer (TTL) regulate the humidity of air entering the
stratosphere, which in turn has a strong influence on the Earth's radiation budget and climate. Jensen
et al. (2013) reported evidence from the 2012 ATTREX program, where a high-altitude NASA Global
Hawk UAV made measurements of water vapor and ice particles in thin cirrus in the TTL. This
presentation integrates measurements from both the 2012 and 2013 ATTREX field campaigns. The
combined results show that two distinct classes of cirrus formed in the tropical tropopause region. (1)
vertically extensive cirrus with low ice number concentrations, low extinctions, and large
supersaturations (up to ~70%) with respect to ice, and (2) vertically thin cirrus layers with much higher
ice concentrations that effectively deplete the vapor in excess of saturation. The persistent
supersaturation in the former class of cirrus is consistent with the long time-scales (several hours or
longer) for quenching of vapor in excess of saturation given the low ice concentrations and cold
tropical tropopause temperatures. The low concentration clouds are likely formed on a background
-1
-1
population of insoluble particles with concentrations less than 100 L (often less than 20 L ), whereas
-1
the high ice concentration layers (with concentrations up to 10,000 L ) can only be produced by
homogeneous freezing of an abundant population of aqueous aerosols. These measurements indicate
that the low concentration cirrus occur frequently in the tropical tropopause region, whereas the high
concentration cirrus occur infrequently. The predominance of the low concentration clouds means
cirrus near the tropical tropopause may typically allow air entry of air into the stratosphere with as
much as ~1.7 times the ice saturation mixing ratio.
Reference: Jensen, E., et al. 2013: Ice nucleation and dehydration in the Tropical Tropopause Layer.
Accepted: Proc. Nat. Acad. Sci.
Page | 529
665
Ice detection with SID-2H during the ICE-T field campaign
1
1
2
Alexandria Johnson , Sonia Lasher-Trapp , Aaron Bansemer
1
Earth, Atmospheric and Planetary Sciences, Purdue University, West Lafayette, United States,
2
MMM, National Center For Atmospheric Research (NCAR), Boulder, United States
Despite numerous advancements in cloud probe instrumentation, the sampling and identification of
small ice particles, particularly in mixed-phase convective clouds, remains a challenge. Initial ice
particles in low concentrations can be difficult to detect, nearly spherical ice particles are often
indistinguishable from water, and clearly identifying the habits of particles smaller than 100 µm has
proven difficult. The Small Ice Detector 2 HIAPER (SID-2H), a relatively new in-situ probe available to
NCAR since 2007, has promise for improving the detection and habit distinction of ice particles
between 2 and 50 µm in diameter. Its use in the ICE-T field campaign was the first in active cumulus
clouds and has allowed for a better understanding of its performance in high liquid content
environments and the errors that arise under such conditions.
The work to be presented will focus on data collected by SID-2H, challenges faced in using these data
to identify small ice, and present a method of correcting for falsely identified ice particles and
coincidence errors. The resulting data are then compared to those collected by other instruments,
including the 2D-C, 3V-CPI, and FSSP-100, and used to identify the 'first detectable ice' in tropical
maritime clouds.
Page | 530
431
Effects of stratospheric aerosol geoengineering on cirrus clouds
1
2
3
Miriam Kuebbeler , Ulrike Lohmann , Johann Feichter
1
2
3
ETH Zurich, Zürich, Switzerland, ETH Zürich, Zürich, Switzerland, Max Planck Institute for
Meteorology, Hamburg, Germany
Geoengineering has become part of public and political discussions about how to prevent dangerous
anthropogenic interference with the climate system. The injection of sulphate aerosols into the
stratosphere in order to cool the climate system was suggested by several prominent climate
scientists. Aerosols injected into the stratosphere can sediment to lower levels into the upper
troposphere, modify the aerosol composition and thus might impact cirrus clouds. Here, we perform
idealized simulations to study the possible impact of stratospheric aerosol on cirrus clouds.
Simulations are performed using the GCM ECHAM5.5 including a two-moment microphysical cloud
scheme which is coupled to the two-moment aerosol scheme HAM. We further couple ECHAM5.5 to a
mixed-layer ocean model (MLO) in order to investigate the impact on the hydrological cycle with the
main focus on cirrus clouds. Our results show in both model set ups that stratospheric aerosol
injections as proposed by several GE approaches will likely lead to changes in the microphysical and
radiative properties of cirrus clouds, however in a rather indirect way: Stratospheric aerosols absorb
near infrared radiation inducing a warming and stabilization of the lower stratosphere and upper
troposphere. Warmer temperatures and reduced vertical velocities decrease the homogeneous
freezing rate efficiently. Cirrus clouds in a geoengineered atmosphere become optically thinner and
exert a negative cloud forcing in the longwave, which accounts for 60% of the overall GE-forcing. This
shows that side effects of stratospheric GE on cirrus clouds exist, may be large and thus need to be
considered in future GE studies. The coupled GCM-MLO studies further confirm that the hydrological
response per degree warming/cooling is larger in case of the GE-forcing than in case of the CO2forcing. That implies that stratospheric aerosol Geoengineering is not able to restore both, temperature
and precipitation, to their respective pre-industrial values.
Page | 531
433
Radiative forcing by aircraft: effects of soot on large-scale clouds
1
2
3
3
4
4
Joyce Penner , Yibin Chen , Cheng Zhou , Yuxing Yun , Ulrich Schumann , Kasper Graf , Olga
5
Popovicheva
1
Atmospheric, Oceanic, and Space Sciences, University of Michigan, Ann Arbor, United States,
2
3
University of Michigan, Ann Arbor, United States, AOSS, University of Michigan, Ann Arbor, United
4
5
States, Deutsches Zentrum für Luft- und Raumfahrt, Oberpfaffenhofen, Germany, D. V. Skobeltsyn
Institute of Nuclear Physics, M.V. Lomonosov Moscow State University, Moscow, Russian Federation
Radiative forcing by aircraft soot in large-scale clouds has been estimated to be both positive and
negative, while forcing by contrails and contrail cirrus (i.e. spreading contrails) is positive. Here we use
an improved model to estimate the forcing in large-scale clouds. We assume that the fraction of soot
particles that have been processed through contrails are good heterogeneous ice nuclei (IN) and use
the average fraction determined from the CoCiP model. The calculated total all-sky radiative climate
-2
forcing ranges between -0.2 and -0.8 Wm , with the range determined by whether sulfate on soot
decreases their ability to act as IN as well as the treatment used for precipitation scavenging. We
discuss what is needed to narrow the range.
Page | 532
B2.1a - The dynamics of extreme events – improving forecasts in the current
climate
10.07.2013 13:15-14:45, Wisshorn
768
Forecast errors associated with diabatic processes in extratropical cyclones
1
2
2
Heini Wernli , Hanna Joos , Erica Madonna
1
2
Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland, ETH Zurich, Zurich,
Switzerland
The prediction of the track, intensity and structure of extratropical cyclones is of key importance for
accurately forecasting intense winds and precipitation associated with these weather systems. In
addition to the primary agents of baroclinic instability, i.e., the horizontal temperature gradient and
typically an upper-level cyclonic vorticity disturbance, moist diabatic processes that occur in saturated
ascending airstreams are essential for the evolution of cyclones, the associated surface weather, and
the downstream flow evolution. A potential vorticity perspective helps explaining how diabatic
processes impact on the dynamics of extratropical cyclones and tropopause-level Rossby waves.
Results from different model validation studies will be shown to illustrate that (i) exceptionally poor
global model medium-range weather forecasts in Europe are associated with errors in the
representation of moist ascending airstreams within North Atlantic cyclones, (ii) during the previous 10
years, the accuracy in predicting the intensity and location of these moist ascending airstreams has
improved for the ECMWF deterministic model, and (iii) that a combination of different microphysical
processes occurring within these moist airstreams is responsible for the overall latent heating and
associated potential vorticity modification. The outlook will emphasize the need for field experiments
dedicated to observing diabatic processes in mid-latitude weather systems and for a systematic
feature-based forecast validation of weather systems with NWP and climate models.
Page | 533
558
Aircraft measurements in warm conveyor belts
1
2
1
2
2
Maxi Böttcher , Andreas Schäfler , Heini Wernli , Reinhold Busen , Andreas Dörnbrack , Christian
1
2
2
3
2
1
Grams , Stefan Kaufmann , Yannik Lammen , Philipp Reutter , Hans Schlager , Harald Sodeman ,
2
Christiane Voigt
1
2
3
ETH Zurich, Zürich, Switzerland, DLR, Oberpfaffenhofen, Germany, University of Mainz, Mainz,
Germany
Warm conveyor belts (WCBs) are coherent air masses that typically ascend from the warm sector of
extratropical cyclones leading to cloud formation and often prominent precipitation. They are
characteristic features of the mid-latitude weather activity. Especially in Central Europe, where the
ascent of WCBs is typically enhanced at the Alps, WCBs repeatedly contribute to severe weather such
as flooding and landslides. In numerical weather prediction models the complex physical processes
along WCBs, including phase transitions of water, radiative effects and embedded convection, are
often not accurately represented, which limits the short and medium-range forecast quality.
In October 2012 the T-Nawdex-Falcon campaign (THORPEX-North Atlantic Waveguide and
Downstream Impact Experiment) took place over Central Europe where aircraft measurements in
WCBs could be performed successfully. For three WCB events mainly in-cloud measurements of
water vapor, total water and trace gases were conducted and dropsondes released. This allows to
verify the evolution of the phases of water during the ascent, and to characterize the water transport
from the planetary boundary layer up to the upper troposphere.
In specifically focussing on performing Lagrangian measurements, that is to measure the same air
mass in different phases of a WCB, we could experimentally quantify Lagrangian changes along the
flow, obtain observations in clouds with different microphysical characteristics, and obtain an overall
picture of the complicated cloud evolution experienced by WCB air parcels along their ascent.
The presentation gives a general overview over the campaign and the WCB systems that were
observed. The sophisticated flight planning procedure is presented, which included different tools
based on trajectory calculations applied to deterministic and ensemble forecasts. Eventually, some
preliminary results will be presented that illustrate the Lagrangian matches between flights and a first
comparison of measurements and ECMWF analysis data.
Page | 534
831
Development processes of Baiu frontal depressions
1
1
Eigo Tochimoto , Tetsuya Kawano
1
Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan
In general, strong baroclinicity is one of the major important factors to extratropical cyclogenesis.
However, the Baiu frontal zone in which a large number of depressions form and develop is
characterized by relatively weak baroclinicity compared to that in other extratropical frontal zones.
Thus, it is worth to examine key factors for the development of Baiu frontal depressions (BFDs).
Tochimoto and Kawano (2012) investigated the development processes of BFDs using a reanalysis
data set. On the basis of the deepening magnitude, 140 BFDs detected in June and July from 2000 to
2007 are categorized into developed and non-developed BFDs. Developed BFDs are further classified
into W-BFDs and E-BFDs; W-BFDs (E-BFDs) peak in the region west (east) of 140°E. They showed
that latent heating is more important factor to the W-BFD development. On the other hand, it is
suggested that low-level baroclinicity makes a larger contribution to the E-BFD development.
In this study, idealized numerical simulations are performed to quantitatively investigate both
contributions of latent heating and baroclinicity to the BFDs development and to understand
remarkable development processes of BFDs. A diagnosis of available potential energy shows that the
effect of latent heating is dominant to the W-BFD development throughout the developing stage, while
baroclinicity as well as latent heating is a large contributor to the E-BFD development. In addition,
evolutions of PV and its production associated with latent heating suggest that W-BFDs have a
remarkable development mechanism. At first, convection occurs near the center of a preexisting lowlevel baroclinic disturbance and then the low-level vortex rapidly develops. The intensified vortex
advects warm and moist air to the front (east) of the vortex center, resulting in activation of convection
there. Thus, the active convective region transfers from the center to the front of W-BFDs.
Page | 535
D2a - A century of international cooperation in geophysics: examples from
IACS and IAMAS
10.07.2013 13:15-14:45, Schwarzhorn
237
The role of geophysicists in scientific internationalism: from the Cold War to
the present
1
Ronald E. Doel
1
History, The Florida State University, Tallahassee, United States
In recent years, scholars have begun to reassess our understanding of the intersection of science with
American foreign policy following World War II. Were state attitudes toward scientific internationalism,
collaboration, and exchange primarily shaped by physicists, or were geophysicists - members of
scientific communities that depend on the sharing of massive amounts of global data - the prime
movers behind these international efforts? To what extent did scientists feel compromised by state
actions involving international scientific activities in the 1950s and 1960s, and what responses did they
take? Was scientific prestige a more important contribution to the start of the Cold War than has
previously been recognized, and are historians only beginning to glimpse significant shifts in
international scientific practices that emerged in this period? And now that the Cold War is over and
the geopolitical situation is experiencing new strains, how might the geophysics community look to the
past to determine the best paths for advancing their research agenda and presenting cogent
arguments for scientific research directly related to a variety of current and potential problems? This
talk assesses current ideas and still-unresolved questions.
Page | 536
426
Jacob Bjerknes: eminent meteorological pioneer and decade-long officer of
IAMAS and IUGG
1
Hans Volkert
1
Institut fuer Physik der Atmosphaere (IPA), Deutsches Zentrum fuer Luft- und Raumfahrt (DLR),
Oberpfaffenhofen, Germany
As is well known in the atmosphreic science community, Jacob BJERKNES (1897-1975) represented
the 3rd generation of the Bjerknes dynasty of scientist following his father Vilhlem (1862-1951) and
grand-father Carl-Anton (1825-1903). His short paper of 1919 "On the structure of moving cyclones"
documented the starting point of the Bergen School of meteorology. From 1940 he worked in Los
Angeles and made important contributions to the description and explanation of the El-Nino
phenomenon over the Pacific ocean. Less known is J. Bjerknes´s long engagement for IAM[AS] (*;
Sec.-Gen. 1936-48; president 1948-51) and IUGG (vice-president 1951-54) before and after his
decision to stay permanently in the United States after German troops had occupied Norway.
The presentation aims at relating J. Bjerknes´s research focus of dynamical meteorology with his
adminstrative service for IAM, inter alia by reference of the IAMAS publication Series #1 and #2 which
chronicle activities of the commissions on Radiation (IRC) and ozone (IOC), respectively. The gradual
tighter combination of dynamic-meteorological techniques with intensive studies of physical processes
is explified, which later became explicitly stated in the extension of the associations name to IAMAP (..
of Meteorology and Atmospheric Physics; Toronto 1957) and IAMAS (... Atmospheric Sciences;
Boulder 1995).
(*) until 1957: IAM - International Association of Meteorology
Page | 537
1242
Cold war, ionospheric research in Greenland, and the politics of rockets
1
Henrik Knudsen
1
Aarhus University, Aarhus C, Denmark
Issued on the front page of Danish newspaper Politiken on July 4, 1968 the lead article announced the
commencement of a joint Danish-American “grand rocket program” to investigate the “splendid natural
phenomena” of sunspots and polar cap absorption from Thule Air Base in northern Greenland. Polar
cap absorption (PCA) is a special phenomenon created when energetic protons from solar flares
penetrate the earth´s atmosphere near the geomagnetic poles. Enthusiasm and national pride ran
high and understandably so even if the scramble for space enjoyed far less public and political support
in Europe compared to its high profile in the two arm wrestling super powers. From the early 1960s
Danish scientist took gradual steps into the field of rocket borne space research e.g. through
participation in rocket launches from Andøya (Norway). Now activities were about to reach a new level
with a joint Danish-American program comprising of no less than 34 rocket launches. The ink was
hardly dry when the same paper the next day reported that the Danish government in a sweeping
move had decided to call of the American part of the joint effort. Only rarely had the Danish
government said no to American research projects in Greenland and never before had rejections
reached the public. In the following weeks newspapers reported from what most participants took to be
a major political mishap by the government. Archival research shows 1) that the role of Danish
scientist in the project was diminutive; 2) that a major agenda was to assess the effects high altitude
nuclear explosions on DoD communication systems; 3) that the Danish government knew about this.
The paper will situate the American rocket project in its Cold War military-technological context and
outline the complex political appropriation process that lead the Danish government to the rejection.
Page | 538
1205
Scientists, gliders, service providers: identities of an atmospheric science
institution in cold war Germany
1,2
Dania Achermann
1
2
Center for Science Studies, Aarhus University Denmark, Aarhus, Denmark, Institut für Physik der
Atmosphäre, Deutsches Zentrum fuer Luft- und Raumfahrt (DLR), Oberpfaffenhofen, Germany
In 1955, the Federal Republic of Germany regained full sovereignty. From then on, there were no
more restrictions on atmospheric research, and several new institutions focusing on the atmosphere
were founded. One of them was the Institute of Atmospheric Physics (IPA) in Bavaria. Emerging from
a research institution for gliding, it was officially established in 1962. But its existence was by no
means secure. Changing political circumstances and public needs, a competitive research landscape,
and new technological developments forced the young institute to adjust its research agenda to get
funding. It was of crucial importance to gain a recognisable profile as an indispensable institution in
the German research landscape. But how did an atmospheric research institute like the IPA develop
an identity and under which circumstances has it changed? To answer this question, I have
investigated the development of the IPA's 1950's-era predecessor, which was established as a glider
association. The gliding tradition had determined its research agenda, but as motorized flight was
permitted once again and with the changing political situation, gliding no longer justified additional
funding. Under ministerial pressure, the institute had to broaden its perspective and take up new, more
relevant research topics. However, so as not to lose flying as its main characteristic, the new topics
had to be chosen carefully. It turned out that airplanes, on the one hand, restricted the range of new
research fields, but on the other, enabled the institute to carry out research that other German
organisations could not. For example, measuring radioactive fallout in the free atmosphere fell into this
category. By analysing the IPA's history, I show that research technologies such as airplanes played
an important factor in the identity building process of the institute, simultaneously determining the
direction of research and being determined by the institute's self-positioning.
Page | 539
235
World Weather Watch: scientific and geopolitical considerations
1
Kristine Harper
1
History, Florida State University, Tallahassee, United States
During the height of the Cold War, the Lyndon Baines Johnson administration decided to take part in
the development of World Weather Watch - a proposed effort to share global meteorological
information that involved the World Meteorological Organization, ICSU, and IUGG. Although those of
us in the scientific community tend to look at the sharing of weather information as being of vital
importance to the atmospheric sciences, it was also important to Johnson's foreign policy efforts to pull
non-aligned countries into the United States' sphere of influence. One item crucial to its success,
however, was the World Weather Link - dubbed the “cool line” - to link data centers in the US and the
USSR. While sharing weather data may seem routine now, this project involved classified cables, high
level diplomatic efforts, and discussions about who would gain more from the shared data - the US or
the USSR. The creation of this “cool line” in the “hot line” times of the 1960s was not guaranteed. This
paper will explore the diplomatic and foreign policy desires behind a seemingly straightforward
scientific endeavor, and why over forty years later, scientists still need to keep track of geopolitical
considerations when organizing internationally cooperative scientific efforts.
Page | 540
C5.2c - Changing snow and ice hydrology in mountain watersheds
10.07.2013 13:15-14:45, Seehorn
1085
Retrievals of mountain snow depth, water equivalent, albedo, grain size and
radiative forcing by light absorbing impurities
1
1
2
3
4
Felix Seidel Caprez , Thomas H. Painter , Jeffrey S. Deems , S. McKenzie Skiles , Annie Bryant , Karl
1
Rittger
1
2
Jet Propulsion Laboratory / California Institute of Technology, Pasadena, United States, National
3
Snow and Ice Data Center, Boulder, United States, University of California, Los Angeles, United
4
States, University of Utah, Salt Lake City, United States
Climate is expected to be most vulnerable in arctic and mountainous regions where the atmosphere
and the hydrosphere meet the cryosphere. A better understanding and quantification of related key
processes are therefore extremely important and requires a combination of modeling and
observational efforts. This will, at the same time, help to improve water resources management and
mitigate the exposure to natural hazards.
The Airborne Snow Observatory (ASO) at NASA's Jet Propulsion Laboratory addresses this need by
establishing new observational capabilities in regional mapping of quantitative mountain snow
properties. We use a laser scanner and an imaging spectometer in combination with comprehensive
retrieval algorithms and field measurements. The assimilation of retrieved snow cover, depth, water
equivalent, albedo, grain size and radiative forcing by light absorbing impurities into water runoff
models can significantly improve their capabilities.
Here, we will present the remote sensing data and retrieval methods as well as a assessment of the
resulting snow products derived from the 2013 ASO campaign in two watersheds of the Sierra Nevada
and the Rocky Mountains, USA. We use the airborne imaging spectroscopy instrument CASI-1500 to
measure the spectral solar radiation reflected from the snow in the visible and near-infrared spectral
region. We also model atmospheric and topographic influences on the solar radiation, the snow
bidirectional reflectance distribution function (BRDF) and the light absorption of ice at 1.03 microns.
The combination of model and observations allows us to determine the spatial distribution of the
mentioned snow properties based on an inversion strategy. Specifically, snow albedo is determined by
generalizing the directional snow surface spectral reflectance with the anisotropy factor given by the
BRDF. The difference of the snow albedo with a modeled clean snow albedo multiplied by the
irradiance provides the spatial distribution of the radiative forcing in snow.
Page | 541
1099
Accuracy of snow depth and SWE estimates from airborne LiDAR and ground
based radar
1
2
2
3
Hans Peter Marshall , Danny G. Marks , Adam H. Winstral , R. Shrestha
1
2
Geosciences, Boise State University, Boise, United States, Northwest Watershed Research Center,
3
Agricultural Research Service, Boise, United States, Geosciences, Idaho State University, Boise,
United States
Accurately estimating of the spatial distribution of snow in mountainous regions at necessary scales
for snow hydrology applications is challenging, as variability in these areas is usually large while
correlation lengths are less than 100 m. Manual measurements are time consuming, therefore direct
in-situ observations at the necessary resolution to capture the true variability at the kilometer scale is
typically cost prohibitive, and occurs only at intensively monitored research sites. Changes in
variability and correlation lengths occur throughout the season, further complicating the ability to
sample the spatial distribution of snow. Recently new techniques have allowed rapid measurements of
snow depth at meter resolution to be performed at km scales and larger, however the absolute
accuracy of these techniques remains poorly quantified. We use 762 manual in-situ measurements of
depth with locations accurate to within 10 cm and coincident with both airborne LiDAR and ground
based FMCW radar, targeted to sample a range of vegetation and snow conditions, to quantify the
accuracy of snow depth estimates from these rapid remote techniques. Accuracy depends primarily on
vegetation due to its affect on both observations, and optimum signal analysis varies with conditions
but also increases the need for user interaction which may not be practical for large scale application.
Using a subset of the in-situ observations to remove bias in the estimates can significantly improve the
accuracy. While ground based radar can achieve higher accuracy as well as estimates of density, the
spatial coverage is much more limited. We discuss the advantages of using both techniques together
to estimate spatially distributed SWE.
Page | 542
1139
Characterizing the spatial snow depth distribution in mountainous terrain
1
1
1
1
1
Nora Helbig , Henning Löwe , Thomas Grünewald , Jan Magnusson , Michael Lehning , Tobias
1
Jonas
1
SLF, Davos, Switzerland
Spatial snow depth information is an essential component for many applications, such as the
computation of snow melt rates in hydrologic applications or the energy balance in meteorological or
climate models. Due to computational constraints, small-scale distributed modeling is rarely feasible
for large regions. This is especially true over mountainous, complex terrain. Sub grid
parameterizations for spatial snow depth distributions are therefore particularly valuable in the context
of large-scale applications.
Past research has shown that for rather homogeneous landscape units the pre-melt spatial distribution
of snow depth can be approximated by a log-normal distribution. However, this is no longer valid for
wind-shaped snow distributions over landscape units covering complex terrain. Seasonally recurring
snow accumulation patterns have been reported, mostly shaped by terrain and wind. We focus on
large heterogeneous landscape units in order to investigate the impact of topographic parameters on
sub grid snow depth distribution at peak of winter with sub grid cells on the order of 25 m. We analyze
a new data