WORLD METEOROLOGICAL ORGANIZATION
WORLD WEATHER RESEARCH PROGRAMME
WWRP 2008 - 1
ABSTRACTS of PAPERS for the FOURTH WMO
INTERNATIONAL WORKSHOP on MONSOONS (IWM-IV)
(Beijing, China, 20-25 October 2008)
WMO TD No. 1446
CLOUD-CLUSTER-RESOLVING ATMOSPHERE MODELING
– A CHALLENGE FOR THE NEW AGE OF TROPICAL
METEOROLOGY
Taroh MATSUNO and the NICAM team
Frontier Research Center for Global Change (FRCGC)
Japan Agency for the Marine-Earth Science and Technology (JAMSTEC)
ABSTRACT
Necessity of explicitly reproducing convective cloud systems in the tropics in global
modeling of the atmosphere is discussed through re-examinations of past and current modeling
studies and underlying conceptions. Responding to the necessity an ultra-high resolution
(3.5km-7km mesh) global atmosphere model, NICAM has been developed at the FRCGC. Quick
results from cloud-cluster-resolving simulations by use of NICAM are briefly described including
simulations of convections with diurnal cycle, super cloud clusters (convectively coupled equatorial
waves), a phase of the Madden Julian Oscillation and generation of tropical cyclones. Discussions
for need of furthering these attempts are given.
1
DIURNAL CYCLE OF MONSOON CONVECTION
Richard H. JOHNSON
Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA
1
INTRODUCTION
The diurnal cycle of precipitation is a dominant feature of all global monsoon systems,
ranging from the world‟s most energetic monsoon – the Asian Monsoon – to the monsoon systems
of the Americas and Africa. On the largest scales, continental mountain ranges generate significant
diurnally varying circulations, vertical motion, and diabatic heating features (e.g., the Tibetan
Plateau in Asia, the Andes over South America). On the mesoscale, localized land and sea breezes,
mountain/valley circulations, and surface heterogeneities influence the diurnal cycle of precipitation
patterns. In general, precipitation tends to be a maximum over land during the daytime and over the
adjacent ocean areas at night; however, there are significant regional variations in this behavior.
The mechanisms for the diurnal cycle of precipitation are varied and complex. This paper reviews
progress in understanding the diurnal cycle of convection, with an emphasis on the most prominent
monsoon system, the Asian monsoon.
2
SIMULATION OF SYNOPTIC AND SUB-SYNOPTIC SCALE
PHENOMENA ASSOCIATED WITH THE EAST ASIAN
MONSOON USING A HIGH-RESOLUTION GCM
NGAR-CHEUNG LAU
Geophysical Fluid Dynamics Laboratory/NOAA, Princeton University, New Jersey, USA
Email: [email protected]
ABSTRACT
An assessment is made on the performance of a global atmospheric general circulation
model with a horizontal resolution of approximately 55 km in reproducing various small-scale
phenomena related to the East Asian monsoon.
In accord with observations, the simulated summer monsoon rains in the East Asian sector
are organized about zonally elongated „Meiyu-Baiu‟ (Plum Rain) systems. A detailed case study is
performed on a prominent rainy episode in the simulation. The model is capable of reproducing the
observed intense gradients in temperature, humidity and moist static stability in the vicinity of the
Meiyu-Baiu front. The axis of the Meiyu-Baiu rainband in this event is aligned with the trajectory of a
succession of mesoscale cyclonic vortices, which originate from southwestern China and travel
northeastward over the Yangtze River Basin.
Analysis of the synoptic development during a severe wintertime cold air outbreak over East
Asia demonstrates the ability of this model to simulate the southeastward advance of intense cold
fronts. The patterns of sea level pressure and surface temperature changes in the vicinity of these
fronts on daily and hourly time scales are in accord with observations.
3
SOUTH ASIAN MONSOON: INTERANNUAL VARIATION
Sulochana GADGIL1, M RAJEEVAN2, Lareef ZUBAIR3
and Priyanka YADAV1
1
Centre for Atmospheric and Oceanic Sciences, Indian Inst. of Science, Bangalore, India
2
National Atmospheric Research Laboratory, Tirupati, Andhra Pradesh, India
3
International Research Institute for Climate and Society, Palisades, New York, USA
1.
INTRODUCTION
The last decade witnessed a surge in Asian Monsoon research and predictions. Pant and
Rupakumar (1997) reviewed the South Asian climate and its variability. Recent reviews elucidated
the advances in understanding and prediction of the variability (Chang et. al. 2005, Wang 2006,
Ding 2007). Intraseasonal variability was reviewed by Lau and Walisser (2005), and synoptic
weather by Ding and Sikka (2006). Better understanding and prediction of ENSO has led to a major
thrust on seasonal to interannual predictions for tropical regions. This paper focuses on the
interannual variation of seasonal rainfall in the Indian summer monsoon rainfall (ISMR), which has a
large impact on the agricultural production and economy. The contribution of agriculture to the
Gross Domestic Product (GDP) decreased substantially since independence, but the impact of
monsoon on the economy has not decreased. A recent analysis revealed that the impact of severe
droughts on GDP has remained between 2 to 5 % of GDP throughout (Gadgil and Gadgil 2006). A
significant finding is the asymmetry that the impact on food-grain production and the GDP of deficit
rainfall being larger than that for surplus rainfall. This is probably because strategies that allow
farmers to reap benefits of good rainfall years are not economically viable. Such strategies (e.g.,
adequate investments in fertilizers and pesticides over rain-fed areas) would become economically
viable if reliable predictions for „no droughts‟ could be generated. Thus prediction of Indian summer
monsoon rainfall (ISMR) and particularly the extremes (i.e. droughts and excess rainfall seasons)
continues to be extremely important.
Quantitative predictions of the summer monsoon rainfall over the Indian region have been
generated from the early thirties since the pioneering efforts of Sir Gilbert Walker. Gadgil et. al
(2005) suggested that empirical and numerical model predictions have not been satisfactory,
particularly on predicting the extremes. New approaches are being developed but whether they
take into account the inherent nonlinearity (e.g. Rajeevan et. al 2006) will be a key question. The
extent ENSO prediction contributes to the interannual variation of rainfall needs be determined. The
strong link of ISMR with ENSO, with increased droughts during El Nino and excess rainfall during
La Nina, is well known (e.g., Sikka 1980, Pant and Parthasarathy 1981,Rasmusson and Carpenter
1983 and subsequent studies). In addition, recent studies (Gadgil et.al 2004, Ihara et al 2007)
showed that, Equatorial Indian Ocean Oscillation also plays a role in the extremes of the ISMR. We
study the links of the rainfall in other South Asian countries i.e. Bangladesh, Pakistan and Sri Lanka
to these two modes and explore the possibility of generating predictions of seasonal rainfall on the
basis of these links.
4
THE MEIYU WEATHER SYSTEM IN EAST ASIA: BUILD-UP,
MAINTENANCE AND STRUCTURES
DING Yihui, LIU Yunyun, ZHANG Li, LIU Junjie, ZHAO Liang
and SONG Yafang
National Climate Center, China Meteorological Administration, Haidian District, Beijing, China
E-mail: [email protected]
ABSTRACT
The Meiyu weather system consists of five components: the Meiyu front or the subtropical
front, the East Asian summer monsoonal airflow, cold airs coming from mid-and high latitudes, the
transverse circulation across the Meiyu from and mesoscale vortices. The build-up of the Meiyu
season is characterized by a teleconnection mode with the onset of summer monsoon over western
coast of the Indian peninsula with an abrupt change or adjustment of the Asian monsoon circulation
features. At the same time, the high potential vorticity (PV) cold air coming from upper troposphere
and lower stratosphere at mid-and high latitudes intrude in the Meiyu region with intraseasonal
low-frequency mode and strongly couples with the monsoonal airflow, thus enhancing the positive
vorticity of air column and modifying the atmospheric stratification. Afterwards, the Meiyu front
becomes stationary in the Yangtze River basin with the unstable atmosphere and a secondary
circulation across the front is produced which can excite the persistent heavy rainfall processes in
the region of ascending motion between the right quadrant of entrance area of the upper westerly
jet streak and the left sector of low-level jet embedded in the East Asian monsoonal airflow. Along
the near-zonally oriented Meiyu front, the mesoscale vortices may frequently form and they can
significantly enhance the Meiyu rainfalls, as producers of excessively heavy rainfalls. Thus, the
Meiyu weather system is a multi-scale interactive complex system.
5
FIELD EXPERIMENTS ON MEIYU/BAIU FRONTAL
PRECIPITATION SYSTEMS AND HEAVY RAINFALLS OVER
YANGTZE RIVER, EAST CHINA SEA AND KYUSHU, JAPAN
Hiroshi UYEDA
Hydrospheric Atmospheric Research Center, Nagoya University, Japan
E-mail: [email protected]
ABSTRACT
Recent field experiments on heavy rainfalls along the Meiyu/Baiu front from Yangtze River
to Kyushu, Japan, are reviewed. Doppler radar observations revealed characteristic of precipitation
systems along the Meiyu/Baiu front. Basic studies on characteristics of precipitation systems in the
region are introduced. Tasks for the future are discussed to understand weather phenomena
relating to heavy rainfalls in East Asia.
6
AN OVERVIEW OF SOWMEX/TIMREX AND ITS OPERATION
Ben Jong-Dao JOU1, Wen-Chau LEE2, and Richard H. JOHNSON3
1
Pacific Science Association c/o Naval Postgraduate School Code MR/CP, Monterey, CA, USA
2
National Center for Atmospheric Research, Boulder, CO, USA
3
Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA
ABSTRACT
This paper is to introduce the goal, the scientific objectives and the operation of Southwest
Monsoon Experiment (SoWMEX) and the Terrain-induced Monsoon Rainfall Experiment (TiMREX)
joint field program. The field program is to study the mesoscale environment and microphysical
structure of precipitation systems over the South China Sea and the surrounding terrain during the
East Asian summer monsoon. The goal of the program is try to improve the understanding of
orographically-induced heavy rain processes and to establish the ability of quantitative precipitation
forecasting in order to meet the urgent need for disaster reduction due to heavy rain.
7
TROPICAL CYCLONE CHARACTERISTICS AND MONSOON
CIRCULATIONS: FIELD PROGRAMS AND OBJECTIVES
Patrick A. Harr1, Johnny C. L. Chan2
1
Department of Meteorology, Naval Postgraduate School, Monterey, CA, USA
E-mail: [email protected]
2
Department of Physics and Materials Science, City University of Hong Kong, Hong Kong, China
E-mail: [email protected]
ABSTRACT
The large-scale environmental characteristics that are favorable for tropical cyclone
formation are typically found to occur over most ocean basins that contain a monsoon system.
Although the favorable conditions occur consistently in the monsoon basins, tropical cyclone activity
is closely tied to variability in the monsoon that provides favorable or unfavorable modifications to
the basic environmental characteristics. This variability may occur over interannual, intraseasonal,
and synoptic time scales. Therefore, it is important to understand the various linkages between
monsoon variability an tropical cyclone activity in each monsoon basin.
In this summary, tropical cyclone activity is related to monsoon characteristics in each
monsoon ocean basin. This includes basic synoptic models of monsoon circulations and their
variability on a variety of space and time scales. The physical relationships between variability in
monsoon circulations and in tropical cyclone activity are summarized
Over recent years, several international field programs have been conducted or are planned
to be conducted to investigate various interactions among factors that link tropical cyclone activity
and monsoon circulations. The primary programs have been conducted over the tropical western
North Pacific. These programs include the THORPEX-Pacific Asian Regional Campaign (T-PARC)
and the Tropical Cyclone Structure – 2008 (TCS-08) programs during August-September 2008. The
science objectives, observing platforms, and facilities associated with these programs are
summarized.
8
AIRBORNE RADAR OBSERVATIONS OF HEAVY
PRECIPITATION SYSTEMS INFLUENCED BY MONSOON
Wen-Chau LEE1, Ching-Hwang LIU2
1
Earth Observing Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
2
Naval Postgraduate School, Monterey, CA, USA
ABSTRACT
The advancement in the understanding of TCs via airborne radar observations since 1975 is
reviewed in this manuscript, focusing on new findings after 2000. The progress in sampling strategy
and analysis techniques to deduce TC kinematic structures is discussed. The TC kinematic and
dynamic processes are studied by decomposing the TC circulations into area averaged mean wind,
axisymmetric, and asymmetric structures in a cylindrical coordinates. Individual storm structures
have been resolved compared with the composite studies from many storms in the pre-airborne
Doppler radar era. These improved TC structures permit the examination on barotropic instability,
vortex Rossby wave, and vortex dynamics from real data. The observations in RAINEX advanced
the understanding in concentric eyewalls, rainband structures, and asymmetric precipitation
structures under the influence of vertical wind shear. In the near future, the primary research focus
is on TC genesis with field experiments such as T-PARC and PREDICT using airborne radars to
sample the key convective processes governing the TC genesis processes.
9
CONCEPT OF GLOBAL MONSOON
Bin WANG1, Qinghua DING1, and Jian LIU2
1
Department of Meteorology and International Pacific Research Institute, School of Ocean and Earth Science
and Technology, University of Hawaii at Manoa, Honolulu, HI, USA.
2
State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology,
Chinese Academy of Sciences, Nanjing, China.
ABSTRACT
Monsoon is one of defining features of Earth‟s climate. This paper discusses an emerging
concept of global monsoon (GM) and demonstrates that the GM precipitation is a sensible measure
of global climate variations in the last millennium. The GM is a response of the coupled
atmosphere-land-ocean-creosphere-biosphere system to annual variation of solar radiative forcing.
In the context of climatology, the GM can be quantitatively described by the sum of a solstitial mode
and an equinoctial asymmetric mode. Global monsoon domain can be delineated by the annual
range (local summer-minus-winter) of precipitation that exceeds 2 mm/day and 70% of the annual
mean. The year-to-year variability of the GM can be measured by GM precipitation (GMP) intensity,
which represents the averaged annual range of precipitation in the GM domain. Using GPCP data,
we found that GMP has significantly increased in the past 29 years (1979-2007). By studying the
millennial simulation with the ECHO-G model, we show that on the centennial-millennial timescale,
the change of the GMP follows the effective radiative forcing better than the change of global mean
surface air temperature, suggesting that the GMP is a valuable gauge for global climate change.
Understanding the integrated property of the GM provides a linkage between paleomonsoon,
modern monsoon, and future monsoon studies. Further research is required to better understand
fundamental dynamics governing the GM system and the linkage and differences among regional
monsoons.
10
SEASONAL PREDICTION OF
AUSTRALIAN SUMMER MONSOON RAINFALL
Harry H. HENDON, Eunpa LIM, and Matthew C. WHEELER
Centre for Australian Weather and Climate Research
Bureau of Meteorology, Melbourne Australia
1.
INTRODUCTION
Seasonal prediction of Australian climate has a long history (e.g., Quayle 1929), in part due
to the strong and persistent influence of El Niño/Southern Oscillation (ENSO; e.g., Nicholls and
Woodcock 1981). Numerous empirical forecast schemes for seasonal rainfall, which capitalize on
the persistence and predictability of ENSO, have been developed (e.g., Nicholls et al. 1982). Some
schemes are skilful enough to justify operational usage by the Bureau of Meteorology National
Climate Centre (e.g., Drosdowsky and Chambers 2001). Empirical forecast schemes typically have
most skill during winter/spring and are least successful during summer, especially in the monsoon
region of tropical north Australia. Dynamical coupled model forecasts of seasonal monsoon rainfall,
as will be shown below, also exhibit better skill in the pre-monsoon season than during the heart of
the monsoon. We review here the basis for skilful prediction of pre-monsoon rainfall and postulate
that skilful prediction of rainfall during the monsoon is limited by local air-sea interaction.
11
THE SOUTH AMERICAN MONSOON SYSTEM
Brant LIEBMANN1 and C. Roberto MECHOSO2
1
Cooperative Institute for Research in Environmental Sciences (CIRES), Boulder, Colorado, USA
2
Department of Atmospheric and Oceanic Sciences, University of California Los Angeles, USA
ABSTRACT
The main characteristics of the South American monsoon system are reviewed. Summer is
the wet season for most of the continent, although the wet season rain rates are somewhat smaller
than those in other continental monsoons. According to some diagnostics, the wet season begins in
early October over the Brazilian highlands and spreads northward. The annual cycle of precipitation
is most pronounced in the southern Amazon. Some of the largest seasonal rainfall occurs there,
with an extension to the southeast known as the South Atlantic convergence zone. Precipitation in
this area is out of phase with that farther to the south and is driven synoptically, although
intraseasonal variations are evident, including associations with the Madden-Julian oscillation. The
El Niño / Southern Oscillation the largest known forcing of interannual variability, is related to
decreased precipitation near the Equator and increased precipitation in east-central South America
Within an ENSO cycle, large subseasonal changes also occur as a result of surface feedback.
Although improving, the present-day climate in coupled models is still not well-simulated and
remains an impediment to improved climate forecasts.
12
THE EAST ASIAN WINTER AND MARITIME CONTINENT
MONSOON
C.-P. Chang1, M.-M. Lu2, F. Tangang3, B. Wang4, E. Aldrian5, T. Y. Koh6,
and L. Juneng3
1
Dept. of Meteorology, Naval Postgraduate School, Monterey, California, USA
Pacific Science Association, c/o Code MR/CP, NPS, Monterey, California, USA
3
School of Environmental and Natural Resource Sciences, National Univ. of Malaysia
4
Dept. of Meteorology, Univ. of Hawaii, USA
5
Agency for Assessment and Application of Technology, Jakarta, Indonesia
6
School of Physical and Mathematical Sciences, Nanyang Technological Univ., Singapore
2
ABSTRACT
The midlatitude component of the of the East Asian winter monsoon (EAWM) is
characterized by the cold-core Siberian-Mongolian high (SMH) at the surface whose variability
affects all scales of the extratropical circulations. The SMH was weakening in recent decades,
which appears to correlate with the negative phase of NAO/AO due to increased warm air advection
over the Eurasian continent and the resultant reduction in snow cover. However, it is not clear that
this recent decrease in the EAWM intensity is unique in the most recent 400 years. Periodical cold
air outbreaks that cause high-impact weather are associated with the intraseasonal and synoptic
variation of the SMH, and they often continue as cold monsoonal surges into the tropics and affect
the tropical component of the EAWM. There is some evidence that intraseasonal variability has
decreased in recent decades although extreme weather events in the past few years counter this
trend. An important mechanism for the intraseasonal and higher frequency enhancement of the
SMH comes from upper level blocking ridges over the Atlantic and the Pacific. The Atlantic blocking
triggers a Rossby wave train that has a downstream effect of enhancing the SMH. The Pacific
blocking forces the SMH through slow retrogression of the blocking center.
The tropical component of the EAWM is the wet phase of the Maritime Continent monsoon.
The region is situated bewteen the Asian and Australian summer monsoon and its annual cycle is
characterized by two asymmetries, both due to complex wind-terrain interactions: 1) Only the boreal
winter monsoon intrudes significantly across the equator into the summer monsoon regime. 2) The
convection center marches from the Indian to the Australian monsoon in boreal fall but the reverse
march is stopped at the equator, leading to sudden onsets in the Asian summer monsoon. The
Maritime Continent rainfall has a complex relationship with ENSO in which the best correlations
occurs in the dry and transition seasons. During the boreal winter wet season regions east of
central Borneo maintain some degree of negative correlation with Nino3 SST but in regions to the
west the correlation is insignificant. These variations are due to the interaction between winds and
the complex togography and also influences from regional SSTs. There are very few systematic
studies on decadal variations. In the intraseasonal and synoptic scales the region is heavily
influenced by MJO and cold surges, which can interact with each other as well as with in-situ
synoptic circulations sytems such as the Borneo vortex. Results of these interactions often leads to
high-impact weather such as torrential rainfall, flash floods, and severe storms including in one rare
case a typhoon.
13
MODELLING MONSOONS: UNDERSTANDING AND
PREDICTING CURRENT AND FUTURE BEHAVIOUR
Julia SLINGO1,2, Alessandra GIANNINI3, M. KIMOTO4,
Roberto MECHOSO5, Jerry MEEHL6, Ken SPERBER7, Andrew TURNER1
1
NCAS-Climate, Walker Institute for Climate System Research, University of Reading
2
Met Office, Exeter
3
IRI for Climate and Society - The Earth Institute at Columbia University
4
CCSR, University of Tokyo
5
UCLA Atmosphere and Ocean Sciences
6
NCAR, Boulder
7
PCMDI, Lawrence Livermore
ABSTRACT
The global monsoon system is so varied and complex that understanding and predicting its
diverse behaviour remains a challenge that will occupy modellers for many years to come. Despite
the difficult task ahead, an improved monsoon modelling capability has been realized though the
addition of more detailed physics of the climate system in our numerical models. Perhaps the most
crucial factor to date has been the development of coupled ocean-atmosphere models. From
subseasonal to interdecadal time scales, only through the inclusion of air-sea interaction can the
proper phasing and teleconnections of convection be attained with respect to sea surface
temperature variations. Even then, the response to slowly varying forcings (e.g., ENSO) do not
result in a robust solution as there are a host of competing modes of variability, including those that
appear to be chaotic, that must be represented. Understanding the links between monsoons and
land surface forcing is not as mature as that explored regarding air-sea interaction. A land surface
forcing signal is associated with the onset of wet season rainfall over the North American monsoon
region, though the relative role of ocean vs. land forcing remains a topic of investigation. Also,
improved forecasts have been made during periods in which additional sounding observations are
available for data assimilation. Thus, there is untapped predictability that can only be attained
through the development of a more comprehensive observing system. Additionally, improved land
surface parameterizations, as well as, for example, convective, cloud, radiation, and boundary layer
schemes are essential to realize the full potential of monsoon predictability. Included in such model
improvements is the need to more comprehensively assess the impact black carbon aerosols,
which may modulate the impact of anthropogenic greenhouse gases. Dynamical considerations
require increased horizontal resolution, to at least T106 (~1 degree longitude vs. latitude), in order
to resolve many monsoon features including, but not limited to, Mei-Yu sudden jump, low-level jet
orientation and variability, and orographic forced rainfall. These goals continually push computing
resources to their limit, thus requiring a continuous upgrade to our computational infrastructure to
ensure progress in understanding and predicting current and future behaviour of monsoons.
14
IMPROVING MULTIMODEL FORECAST OF MONSOON
WEATHER OVER CHINA USING THE FSU SUPERENSEMBLE
T. N. KRISHNAMURTI, Anitha D SAGADEVAN, Akilesh K MISHRA
Department of Meteorology, Florida State University, Tallahassee, FL, USA
ABSTRACT
In this paper we present the current capabilities for Numerical Weather prediction of
precipitation over China using a suite of ten multimodels and our Superensemble based forecasts.
Our suite of models include the operational suite selected by NCARs TIGGE archives for the
THORPEX Program. These are: ECMWF,UKMO, JMA ,NCEP,CMA,CMC,BOM,MF, KMA and the
CPTEC models.( The acronyms are explained in a table within this paper). The superensemble
strategy includes a training and a forecasts phase, for these the periods chosen for this study
include the months February through September for the years 2007 and 2008. This paper
addresses precipitation forecasts on the medium range ie out to day 10 of forecasts using this suite
of global models. For training and forecasts validations we have made use of an advanced TRMM
satellite based rainfall product. We make use of a standard metrics for forecast validations that
include the rms errors, spatial correlations and the equitable threat scores.The results of skill
forecasts of precipitation clearly demonstrate that it is possible to obtain higher skills for
precipitation forecasts for days 1 through 10 of forecasts from the use of the multimodel
superensemble as compared to the best model of this suite. Those skills are shown for a global belt
and especially over China. Phenomenologically this product was also found very useful for features
for 5 to 10 day forecasts for the Onset of the South China Sea monsoon, the life cycle of the Meiyu
rains and post typhoon landfall heaving rains and flood events. The higher skills of the multimodel
superensemble makes it a very useful product for such real time events.
15
INTRASEASONAL VARIABILITY AND FORECASTING:
A REVIEW OF RECENT RESEARCH
B. N. GOSWAMI1, M. C. WHEELER2, J. C. GOTTSCHALCK3,
D. E. WALISER4
1
Indian Institute of Tropical Meteorology, Pune, India
Centre for Australian Weather and Climate Research, Bureau of Meteorology, Melbourne, Australia
3
Climate Prediction Center, NOAA/National Weather Service, Washington D.C., USA
4
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, USA
2
1.
INTRODUCTION
A paradigm shift is underway in the way we look at the monsoon systems of the world. While
traditionally monsoons have been characterised by seasonal means, the sub-seasonal oscillations
with time scales longer than synoptic but shorter than seasonal, known as intraseasonal variability
(ISV), have emerged as the primary building block for monsoon systems. ISV manifests as „active‟
and inactive or „break‟ spells within the monsoon seasons that have tremendous impact on
agricultural production, water resource management, and other weather-sensitive industries. This
paradigm shift arises from the realization that while on one hand the ISV influences predictability of
the seasonal mean climate (Goswami and Ajaya Mohan 2001), it also influences weather
predictability by modulating the frequency of occurrence of synoptic events such as lows,
depressions and tropical cyclones (Maloney and Hartmann 2000; Goswami et al. 2003; Bessafi and
Wheeler 2006). The amplitude of ISV is much larger than that of the interannual variability (IAV) of
the seasonal mean and comparable to that of the seasonal cycle (Fig.1, illustrated in the context of
the Indian monsoon; see Waliser 2006a for global maps), thus providing optimism for extended
range prediction. Quantitative estimates of potential predictability of ISV (Waliser et al. 2003;
Goswami and Xavier 2003) indicate the limit of useful skill of predicting the active-break spells may
be extended to 25-30 days. Recognition of the importance of ISV in the climate system led to the
comprehensive review of all aspects of ISV of different monsoon systems in Lau and Waliser
(2005).
High potential usefulness of intraseasonal forecasts for agriculture, society and economy
has triggered a number of research activities to develop empirical as well as dynamical models for
extended range prediction of ISV. During the past few years better characterization of the observed
space-time structures of the Madden-Julian Oscillation (MJO; Zhang 2005) and the associated
fluctuations of the tropical convergence zone (TCZ) and underlying convectively-coupled waves, all
of which affect the Asian and Australian monsoons, have evolved. The greater recognition and
understanding of these factors, coupled with demonstration that ocean-atmosphere coupling adds
some additional memory to both the MJO and Indian monsoon ISV (e.g. Hendon 2005), has led to
development of some empirical models for extended range prediction. While some of these models
demonstrated excellent hindcast skill, until recently most of them could not be used for operational
real-time forecasts. In this chapter, some recent developments on real-time prediction of ISV of
Indian summer monsoon (section 2) and the Australian monsoon (section 3) are highlighted. While
the skill of dynamical models still generally lags that of empirical models, gains are being made and
the efforts in this direction by operational Centres are summarized in section 4.
16
INTRASEASONAL PREDICTION AND PREDICTABILITY
FOR BOREAL WINTER
In-Sik KANG and Hye-Mi KIM
Climate Environment System Research Center, Seoul National University, Seoul, Korea
ABSTRACT
The objective of this paper is to assess the predictability of intraseasonal variation (ISV) by
using various statistical and dynamical models available at present with rigorous and fair
measurements. For the fair comparison, the real-time multivariate Madden-Julian Oscillation (RMM)
index is used as a predictand for all models. The RMM indices are the time series associated with
the first (RMM1) and second (RMM2) eigenvectors of the combined EOF of the OLR and zonal
wind fields at 200 hPa and 850 hPa over the tropical belt. The statistical models include the models
based on a multi linear regression, a wavelet analysis, and a singular spectrum analysis (SSA).
Here the prediction skill is determined in terms of correlation skill and the prediction limit is defined
as the time point at the correlation skill of 0.5. The prediction limits of RMM1 (RMM2) index are at
day 17-18 (16-17) for the multi regression model, whereas, they are at day 8-10 (10-12) for the
wavelet and SSA based models. The poor predictability of the wavelet and SSA models is related to
the taping problems for a half length of the time window before the initial condition.
To assess the dynamical predictability, long-term serial prediction experiments with a
prediction interval of every 5 days are carried out with both SNU AGCM and CGCM for the 27
(1979-2005) and 8 (1998-2005) boreal winters, respectively. The period of each prediction is for 30
days. The prediction skills are measured using the same predictand and similar prediction
framework as those of statistical models. The prediction limits of RMM1 (RMM2) occur at day 15-16
(17-18) for the AGCM and 18-19 (22-23) for the CGCM. These results demonstrate that the
dynamical prediction skill are not lower than those of the statistical predictions and is even better
when the CGCM is used. The dynamical and statistical predictions are combined using a Bayesian
method. The prediction skill of the combined prediction shows that the skill is superior to any of the
statistical and dynamical predictions over entire forecast lead days.
17
IMPACTS OF CLIMATE CHANGE ON ASIAN MONSOON
CHARACTERISTICS
Akio KITOH
Meteorological Research Institute, 1-1 Nagamine, Tsukuba, Ibaraki, Japan
E-mail: [email protected]
1.
INTRODUCTION
Future climate projections based on non-mitigation scenarios are assessed in IPCC (2007a),
where models are consistent in projecting increased precipitation in the tropics and in high-latitudes,
and decreased precipitation in the subtropics. In short, wet areas in the present-day climate
conditions become wetter and dry areas drier. Figure 1 shows the projected changes in multi-model
mean seasonal mean precipitation at the end of the 21st century for the SRES A1B scenario from
phase 3 of the Coupled Model Intercomparison Project (CMIP3) experiments (IPCC 2007a). In DJF,
it shows a large increase in the tropics, an increase in the mid- and high-latitudes and a decrease in
the subtropics, particularly over north Pacific subtropical region and the Mediterranean region.
These features are generally found in each model as shown with dots in the figure where more than
90% of the models agree in the sign of the change. Over the North Pacific, a poleward shift of
precipitation zone is seen, which is associated with a northward shift of mean sea-level pressure
fields. Model consistency is relatively smaller in the tropics, while there is a tendency that models
have positive precipitation anomaly to the east of the present-day precipitation area, that is, a mean
El Niño-like response in the tropical climate.
18
THE WEST AFRICAN MONSOON
Serge JANICOT1, Jean philippe LAFORE2, Chris THORNCROFT3
1
LOCEAN/IPSL IRD, 4 Place Jussieu, 75252 Paris cedex 05 France
E-mail: [email protected]
2
CNRM/GAME Météo-France, 42, Avenue G. Coriolis, TOULOUSE Cedex France
E-mail: [email protected]
3
Department of Earth and Atmospheric Sciences, University at Albany, SUNY, Albany, NY, USA
E-mail: [email protected]
1.
INTRODUCTION
The West African monsoon (WAM) is a coupled atmosphere-ocean-land system
characterized by summer rainfall over the continent and winter drought. The processes that couple
the land, ocean, and atmosphere involve multiple interacting space- and time-scales. Many of the
key scientific questions that relate to these scale interactions cannot be answered using routinely
available observations and reanalysis data sets. This is due to a combination of the sparsity of the
routine observing network over and around West Africa, the need for specialized observations of
various climate system parameters, and the known deficiencies of GCMs used for weather and
climate prediction and relied upon for producing reanalysis.
As with all monsoon systems, the evolving ocean and land conditions are crucially important
for determining the nature of the WAM and its variability. In particular, prospects for improving
seasonal-to-interannual prediction of the WAM heavily rely on the potential predictability of these
surface conditions, our ability to observe key surface variables needed to initialize dynamical
models, and the skill of these models to simulate subsequent evolution of the surface variables.
In this chapter, we begin in section 2 by summarizing the current understanding of the mean
annual cycle of the WAM system. It is very likely that problems GCMs and CGCMs have in
predicting the WAM climate arise through a misrepresentation of the basic mean annual cycle. In
this regard it is important that we understand better the key atmosphere, land, ocean interactions
that take place in association with the annual cycle. In section 3 we will focus our attention on the
variability of the WAM on interannual and longer timescales including how the WAM may change in
the coming century. In sections 4 and 5 we discuss the variability of the WAM at intraseasonal and
weather timescales respectively. The motivation for this is two-fold : (i) There is a need to better
understand key processes associated with the interactions between atmosphere, land and ocean
as well as between dynamics and convection – fundamentally these need to be studied at
intraseasonal and shorter timescales. We believe that model improvements at these timescales will
very likely have positive implications for longer timescales ; and (ii) Almost all societal applications
require information about the statistics of weather systems and so it is important that we improve
our understanding, and ultimately our ability to predict, this variability.
19
EAST ASIAN, INDOCHINA, AND WESTERN NORTH PACIFIC
SUMMER MONSOON
Tianjun ZHOU1, Huang-Hsiung HSU2, Jun MATSUMOTO3
1
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
Pacific Science Association c/o Naval Postgraduate School Code MR/CP, Monterey, CA, USA
3
University of Tokyo, Japan
2
1.
INTRODUCTION
The combination of thermal contrast between the Eurasian continent and Indo-Pacific
Ocean produces a powerful Asian-Australian monsoon (A-AM) system. The monsoons in the East
Asia (EA) and western North Pacific (WNP) regions are essential parts of the integral A-AM system.
The EA monsoon lies downstream of the Tibetan Plateau. The distinctive tectonic setting brings
unique features to the EAS monsoon. The generally recognized EA summer monsoon (EASM)
system consists of East Asian subtropical front, the western North Pacific subtropical high and the
western North Pacific monsoon trough (MT) or the WNP ITCZ. While the EASM is a continental
monsoon component, the WNP summer monsoon (WNPSM) is an oceanic monsoon system. The
prominent circulation features of WNPSM that affect the summer climate in marine East Asia and
the Western North Pacific (hereafter referred to as EA/WNP) are the MT and the subtropical
anticyclonic ridge (ACR). One of key issues to understand the WNPSM variability is to understand
the controlling mechanisms on the MT and ACR.
The EASM and WNPSM exhibit variability in a variety of time scales, ranging from synoptic,
intra-seasonal, interannual, to interdecadal time scales. There have been many studies on the
numerous atmospheric and oceanic features associated with these two monsoon components. The
principal goal of this review is to provide a synopsis on the major progresses in EASM, Indochina
monsoon, and WNPSM studies achieved in recent 5 years, focusing on the climate aspects of the
monsoon components. An account of this review is given to summarize the diurnal cycle of rainfall,
interannual and loner-term variability of monsoon in continental East Asia (Section 2), annual cycle,
sub-seasonal and interannual variability of monsoon in Indochina (Section 3) and western North
Pacific (Section 4). A concluding remark is given in Section 5.
20
CONTRIBUTIONS FROM THE NORTH AMERICAN MONSOON
EXPERIMENT TOWARDS IMPROVED UNDERSTANDING AND
PREDICTION HIGH IMPACT WEATHER AND CLIMATE EVENTS
David J. GOCHIS1, Ernesto H. BERBERY2
1
National Center for Atmospheric Research, Boulder, CO USA
2
University of Maryland, College Park, MD USA
ABSTRACT
Like other global monsoon systems, the North American Monsoon (NAM) exerts a key
control on the warm season hydroclimate of North America, driving high impact events from
weather to climate timescales. It is simultaneously a provider of seasonal rains critical to agriculture
and water resources while also an arbiter of destructive weather events. These events include
heavy rainfall in complex terrain, flash flooding, land-falling tropical storms, dry lightning and fast
moving dust storms, and, every year, result in significant loss of life and property. From a climate
perspective, variability of the NAM system both drives and responds to regional patterns of
sea-surface temperatures, land surface moisture conditions, moisture transport mechanisms, as
well as meso-scale and synoptic scale transient features of the atmosphere. The theme of IWM-IV,
the reduction of disaster risks through improved forecasts of high-impact weather, is put forward at
an ideal time with regard to NAM research as it arrives near the end of a ten-year,
internationally-coordinated research program known as the North American Monsoon Experiment
(NAME). The NAME research program has produced significant advances in understanding of
many NAM processes responsible for mean state and extreme event manifestations of the NAM
climate. Furthermore, NAME has coordinated a series of model evaluation, data impact, and model
forecast assessments as well as societal applications activities which are directly aimed at
improving prediction skill and societal capacity to deal with monsoon climate and weather related
events. This work reviews progress in understanding NAM processes that have been achieved
through the NAME research program. Emphasis is placed on describing new pathways that have
been created which link new or previously unavailable observations and diagnostics to improved
understanding and prediction skill from timescales ranging from a few days to several seasons. The
review concludes with a set of recommendations for improving NAM predictions through the use of
integrated regional climate observing systems as well as a summary of unresolved research
questions which currently inhibit monsoon forecast skill across timescales.
21
SYNOPTIC AND MESOSCALE PROCESSES IN
THE SOUTH AMERICAN MONSOON
Alice M. GRIMM1, Maria Assunção F. SILVA DIAS2
1
Department of Physics, Federal University of Parana, Curitiba, Parana, Brazil
E mail: [email protected]
2
Center for Weather Forecast and Climate Studies CPTEC/INPE, Cachoeira Paulista, SP,
and University of São Paulo, Brazil
E mail: [email protected]
1.
INTRODUCTION
Although the large-scale circulation patterns associated with the South American Monsoon
System (SAMS) are driven by seasonally varying large-scale distributions of sensible and latent
heating, with the Andes Mountains and other orographic features playing an important role in the
dynamics of the monsoon system, there are numerous synoptic and mesoscale features embedded
within these large-scale circulation patterns. These features are responsible for the day-to-day
weather and high impact rainfall events. As extreme rainfall events that affect the most populous
regions in South America are most frequent in the summer monsoon season, understanding
synoptic and mesoscale processes in the SAMS and improving their forecast has important
practical consequences. Some of these features and the factors that can affect their frequency and
intensity are here briefly described, with mention of forecast issues and remaining challenges.
22
THE CHARACTERISTICS OF SUMMER MONSOON RAINFALL
AT THE SOUTHWESTERN OCEAN AREA OF KOREA: A STUDY
OF THE 2007 SEASON
D.I. LEE1, S.M. JANG1, C.H. YOU2, M. JANG1, G.J. SEO1, D.S. KIM1, M.Y.
KANG1, M.K. KIM1, K.E. KIM3, H. UYEDA4, B.H. KWON1 and H.J. YOON5
1
Department of Environmental Atmospheric Sciences, Pukyong National University, Busan, Korea
2
Korea Meteorological Administration, Seoul, Korea
3
Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu, Korea
4
Hydroshperic Atmospheric Research Center, Nagoya University, Nagoya, Japan
5
Department of Satellite Information Sciences, Pukyong National University, Busan, Korea
1.
INTRODUCTION
The rainy season from June to July over the East Asia is referred to Changma in Korea,
Meiyu in China, and Baiu in Japan. During this period the rainfall area elongated from west to east
is called Meiyu-Baiu front or Changma front (a regional difference in locations, timing and duration
in East Asia). The movement of Changma front and mesoscale convective system occurred near
the front frequently lead to severe weather phenomenon such as localized gust and heavy rainfall.
There have been many studies on frontal heavy precipitation, which is sometimes
developed and accompanied with high wind and gusts near those areas (Matsumoto et al. 1971a, b;
Akiyama 1973; Ninomiya 1992). The formation process of frontal systems was influenced by the
moisture transport and convergence of the westerly with the Pacific easterly wind around the South
China Sea and the middle latitude circulation systems (Ninomiya 1978; Tao and Chen 1987;
Ninomiya and Akiyama 1992; Lee et al. 1998; Ding and Johnny 2005).
To clarify the structure and formation process of these frontal precipitation systems several
experiments have been carried out in the East Asia. In Japan, intensive field experiments using
Doppler radars were carried out in Okinawa in 1987, Kyushu Island in 1988, and Kyushu Island and
over the East China Sea between 1998 and 2002(Ishihara et al. 1992; Ishihara et al. 1995;
Kawashima et al 1995; Takahashi et al. 1996; Yoshizaki 2000). In China, the South China Sea
Monsoon Experiment (SCSMEX) was carried out between 1996 and 2001 (Lau et al. 2001; Ding et
al. 2004). The purpose of these experiments is to understand mesoscale feature of frontal systems
formed in the East Asia (Moteki et al. 2004). In Taiwan TAMEX (Taiwan Area Mesoscale
Experiments) was carried out around Taiwan in 1987 (Li et al 1997; Lin et al. 1991; Ray et al. 1991;
Teng et al. 2000). In Korea, the KORMEX (Korean Mesoscale Experiment) was carried out in the
middle of Korean peninsula in 1997 and 1998 (Oh et al. 1997) and the KEOP (Korean Enhanced
Observing Program) was carried out in the southern part of Korean peninsula from 2001 to present
(Choi et al. 2006).
Especially in Korean peninsula, these observation studies are very important because more
than half of annual precipitation over the Korean peninsula occurs during the summer and in this
season the Changma front accompanies with a belt-like peak rainfall zone which developed from
convergence zone between the tropical maritime air mass from the south, and both continental and
maritime polar one from the north (Oh et al. 1997). Some heavy rainfall in Korea is developed from
mesoscale disturbances which originated in China and then propagated eastward along the frontal
system. There have been many studies on the synoptic conditions of this heavy rainfall (Kim et al.
1983; Park et al. 1986; Hwang and Lee 1993; Lee et al. 1998). However, the observation studies
using radar data, focused on the Changma front, and its background field at lower latitude of the
Korean peninsula had been rarely accomplished.
Therefore, in order to find out characteristics of Changma front and its related precipitation
systems, Global Research Laboratory (GRL) of Korean Ministry of Education, Science &
Technology set an intensive observation period (IOP) at Chujado (33.95°N, 126.28°E) from June 21
to July 11 in 2007. Observational network covered over the southwestern coast of Korean peninsula
and the northern part of the East China Sea with 3 Doppler radars, upper-air soundings as shown in
Fig. 1.
23
MESOSCALE ASPECTS OF THE AUSTRALIAN MONSOON
Peter MAY
Centre for Australian weather and Climate Research
– A partnership between the Bureau of Meteorology and CSIRO, Melbourne, Australia
Email: [email protected]
1.
INTRODUCTION
Northern Australia experiences a well defined monsoon during the southern summer
months with marked signals in wind and rainfall (Troup 1961, McBride, 1987). The monsoon has
been studied in many experiments over the past two decades from the Australian Monsoon
experiment (Holland et al, 1986) to the recent Tropical Warm Pool International Cloud Experiment
(May et al., 2008). Within the overall wet season there is substantial intra-seasonal variation
associated with a variety of waves (Madden-Julian Oscillation, equatorial waves etc, e.g. Wheeler
and McBride, 2005 for a review) as well as substantial influences from the mid-latitudes (Keenan
and Brody, 1988; Davidson et al, 2007, Allen et al 2008b). These influences and the dramatic and
sudden changes in regime associated with monsoon onset and breaks mean that the Australian
monsoon is inherently a mesoscale phenomena. Individual cloud systems also show a rich variety
of structure and organisation that evolves on scales of a few hours within a broad definition of
mesoscale. The monsoon onset typically is accompanied by widespread convective activity and a
maximum in area averaged rainfall. This maximum monsoonal rainfall is typically on the northern
side of the trough line except on the east coast of Australia where there is significant orographic
enhancement of rainfall on the south side of the trough.
This summary will begin with a discussion of the transitions from monsoon and break
conditions. The next section will focus on an overview of storm morphology and organisation will be
followed by discussions of some illustrative cases. Note that that tropical cyclones will not be
discussed as a focus in this review, although they produce significant and high impact weather and
are frequently initiated within the active areas of the monsoon.
24
SYNOPTIC AND MESO-SCALE WEATHER DISTURBANCES
OVER SOUTH ASIA DURING
THE SOUTHWEST (SUMMER) MONSOON SEASON
D.R. SIKKA
40 MAUSAM VIHAR, NEW DELHI – 110 051, INDIA
1.
INTRODUCTION
Scientific investigations, with instrumental observations, about the seasonally changing
winds over the north Indian Ocean can be said to have begun in the 16th Century CE. However,
connections of the Southwest monsoon with the summer rainy season over south Asia began to be
understood in the 19th Century and got impetus with the establishment of the India Meteorological
Department (IMD) in 1875. As availability of surface and upper air meteorological data expanded in
the next 100 years and modern technologies of weather radar, weather satellites, ocean observing
systems and computational facilities were introduced in the last 50 years, our understanding and
prediction capabilities have increased enormously. Phenomenological aspects of the South Asian
Summer Monsoon (SASM) began to emerge from the early studies of Blanford (1886) on the
„Rainfall of India‟ in which he had emphasized the predominant role of the surface heat low over
now Pakistan and the moist monsoon trough (MT) stretching from undivided NW India to North Bay
of Bengal, MT the focus where the moist monsoon winds of marine origin converge. The modulation
of MT within the season was ascribed to north south oscillation of the MT with periods of excess
rains (active monsoon) over central India when the MT laid somewhat south of its normal position
and lulls in rain (break monsoon) followed when it shifted northward and hugged the foothills of
Himalayas. It was realized that rains do not occur everyday in the season but has an intra-seasonal
cycle of excess and deficit and Blanford named this as active – break cycle of the Southwest
Monsoon. John Eliot (1884) was able to demonstrate that the onset of the summer monsoon was a
dramatic event in which sudden onrush of regional moist cross-equatorial flow occurred connecting
the near-equatorial flow near the surface of the ocean in the two hemispheres. He also showed that
weather disturbances like tropical cyclones formed at the leading edge of this strong westerly winds
over the north Indian Ocean at the time of onset of the monsoon. He was also able to recognize that
weather disturbances of strength less than the tropical cyclone continued to form over the north Bay
of Bengal in the rest of the season (July, August, September). These low pressure systems (LPSs),
which he called minor storms of the monsoon season, entered mainland India every 3 to 10 day
interval and maintained the spatio-temporal distribution of rains over most of India. This was the first
recognition of the role of synoptic systems in the monsoon processes. Since these very early
investigations, the large scale phenomenology of monsoon has enormously expanded in the last
125 years. Links of monsoonal intra-seasonal (IS) and interannual (IA) fluctuations have been
established with regional and global atmospheric and coupled land-ocean-atmospheric processes.
Meso-scale distributions of heavy rainfall, within the synoptic scale, have been also brought to light
in several studies conducted in the last 3-decades. The components of the global and the Asian
monsoon systems interact with the SASM rather strongly on the planetary scale (30-50 - day)
eastward moving near equatorial Madden Jullian Oscillation (MJO) and the northward propagating
(Sikka and Gadgil 1980, Yasunari 1980 and several others since then) intra-seasonal oscillation
(ISO) of the monsoon. Another low frequency (10-20 day) ISO moving from east to west along
10-200 N over the Indo-Pacific region also modulates monsoon activity (Krishnamurti and Ardunay
1980, Chatterjee and Goswami 2004 and others). It has been now recognized that the SASM has
multi-scalar dimensions with decadal, inter-annual (IA) intra seasonal (IS), synoptic and even
diuranal scales, interacting in a complex manner. Such multi-scalar interactions have yet to be
investigated in a clear and comprehensive manner. These aspects form important objectives of the
campaigns under the Asian Monsoon years (2007-2012) filed program (AMY Science Plan 2008)
and the Indian Continental Trough Convergence Zone (CTCZ) Program (DST 2008). The relative
roles played by the annual cycle of the atmosphere and ocean and their relative timings over the
SASM region have also to be investigated (Goswami etal 2006 a). The timings of the annual cycle
together with land and ocean surface boundary conditions may influence the strength and
frequency of synoptic and meso-scale weather systems to produce a vast variety of rainfall
fluctuations on the IS scale. Even though the contours of ISOs may show much resemblance to
each other year after year the details of the spatio-temporal distribution of summer rains over south
Asia show a vast variety.
25
HEAVY PRECIPITATION EVENTS:
A GLOBAL SURVEY, 1998-2007
Brian MAPES1 and Robert JOYCE2
1
Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, Florida, USA
Email: [email protected]
2
Climate Prediction Center, NOAA, Washington, DC, USA
ABSTRACT
The heaviest precipitation events (here, 1-day and 3-day accumulations) at every location in
the tropics and subtropics have been identified in a 10-year dataset of precipitation estimates at 1/4
degree 3-hourly resolution (the TRMM 3B42 product, based on rainrate-calibrated IR data). Some
basic statistics of amount and seasonality are shown here.
We use this database of record-setting events for selecting case studies. Animations are
made semi-automatically from a Web-accessible satellite imagery archive; the next step will include
adding weather analysis and forecast fields, including ensemble forecasts from the TIGGE archive.
Examination of many cases selected in this objective manner seems like a useful middle ground
between arbitrary case studies and bland statistics, but may require nontraditional forms of
dissemination.
26
MOIST POTENTIAL VORTICITY ANALYSES OF
CONVECTIVE RAINFALL SYSTEMS
Shouting GAO
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
1.
INTRODUCTION
The development of convective rainfall systems is closely related to atmospheric moist
instability, the availability of water vapor, and these systems‟ interaction with their embedding
large-scale environment. Meteorologists have been making consistent efforts to explore these
systems including their origin, structure, and evolution. Significant progress has been made in the
past decades. However detailed physical and dynamic understandings are far from clear and
greatly hindered by the involvement of condensation associated diabatic processes. Therefore here
several recently-developed derivatives of moist potential vorticity (MPV) are introduced here and
their applications in diagnosing the development of convective rainfall systems are further
discussed. Our major purpose is to promote further theoretical and dynamic diagnostic studies of
convective rainfall systems.
27
SOME ASPECTS OF HEAVY PRECIPITATION
RELATING TO TOPOGRAPHY
Seung-Hee KIM and Robert G. FOVELL1
Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles
1.
INTRODUCTION
Severe weather associated with monsoon circulations very commonly involves heavy
precipitation that is often initiated, influenced or abetted directly or indirectly by topography.
Naturally, mountains represent obstacles that can induce or enhance precipitation directly via
mechanical lifting, a phenomenon skillfully represented in “upslope models” (e.g., Smith 2003;
Smith and Barstad 2004). Secondary effects, such as those owing to wave activity provoked by the
forced ascent, can also strongly focus or modulate precipitation (Bruintjes et al. 1994; Garvert et al.
2005). Under certain conditions, the topographic influence can extend far upstream owing to
blocking (e.g., Pierrehumbert and Wyman 1985; Smolarkiewicz and Rotunno 1990), inducing or
augmenting precipitation over a broad distance (Grossman and Durran 1984; Houze et al. 2001).
Mountains can also act as elevated heat sources, complicating the environmental response (Smith
and Lin 1982; Reisner and Smolarkiewicz 1994; Crook and Tucker 2005).
Orography can organize precipitation in the downstream direction as well, in the form of
linear, quasi-stationary rainbands that can substantially augment precipitation (Yoshizaki et al. 2000;
Kirshbaum and Durran 2005). Convective systems induced by topography may subsequently
remain where initiated or propagate away, in either the downstream or upstream directions (Chu
and Lin 2000; Chen and Lin 2005), depending on environmental conditions. Mountains can also
spawn disturbances -- such as shear lines and vortices -- that can bring about sometimes
devastating floods in areas rather far removed from their locale of origin (Tao and Ding 1991; Ding
et al. 2001). Certainly, mountains can present formidable barriers to propagating systems, such as
cold fronts or mesoscale convective systems, which encounter them (Teng et al. 2000; Frame and
Markowski 2006).
This necessarily brief review attempts to touch upon several of these topics, specifically
focusing on a handful of papers the authors find to be particularly instructive or revelatory. This
paper‟s separate sections focus on the influence of terrain upstream, downstream, and at distance
from the topography, and conclude with a brief discussion of the influence of mountains on
approaching weather systems. We trust the reader appreciates that the literature is vaster and
richer than this humble effort can possibly convey.
1
Corresponding author address: Prof. Robert Fovell, UCLA Atmospheric and Oceanic Sciences, 405 Hilgard Ave., Los
Angeles, CA 90095-1565, USA.
28
HEAVY RAINFALL OVER THE BAIU FRONTAL ZONE AROUND
JAPAN- RELATION WITH CLOUD-TOP HEIGHTS OF
CUMULONIMBI T. KATO
Meteorological Research InstituteTsukuba, Ibaraki, Japan
ABSTRACT
The Baiu front is a specific front that is analyzed along a large equivalent potential
temperature e gradient region with the strongest convective activities over the Baiu frontal zone, as
“a result of convective activities”. This is because convective activities lift high e airs flowing into
the Baiu frontal zone and consequently a large e gradient is produced there. Moreover, heavy
rainfall does not necessarily occur around the analyzed Baiu front on weather maps, because the
Baiu front is usually analyzed “as a result of convective activities”.
Heavy rainfall is caused by successive formation of developed cumulonimbi. Environmental
condition that such cumulonimbi can form is often found on the southern side of the Baiu frontal
zone in western Japan. There are three favorable conditions for the development of cumulonimbi as
follows; the inflow of low-level high e airs, less inflow of middle-level airs warmed through
convective activities on the upstream side, and the pre-existence of updrafts over the Baiu frontal
zone. Low-level high e airs is transported to western Japan along the edge of the Pacific high
pressure zone. On the northern part of the Baiu frontal zone, middle-level airs warmed through
convective activities on the upstream side (i.e., over China Continent) are often transported to the
Japan Islands by westerly winds, and they stabilize the latently unstable atmospheric condition
there. On the southern part of the Baiu frontal zone, since such a transportation of warmed airs
appears at a low rate, the atmospheric condition is not usually stabilized and a relatively large lapse
rate maintains there for cumulonimbi to develop higher.
Statistical studies on cloud-top heights of cumulonimbi CTOPs, using objective analysis
data and simulation results of a cloud-resolving model, suggest that major CTOPs appear
separately at different levels below 5 km and above 10 km. This means that either of warm-rain and
cold-rain type cumulonimbi (i.e., low and high developed cumulonimbi) forms dependently on
environmental conditions. Cold-rain type cumulonimbi often form in western Japan in the second
half of the Baiu season (i.e. July), while simulated CTOPs exceeding 10 km appear at a
considerably lower rate than those below 5 km. However, the contribution rate to total rainfall
amount of cold-rain type cumulonimbi is comparable with that of warm-rain type ones. On the other
hand, in the first half of the Baiu season (i.e., June), CTOPs exceeding 10 km are rarely simulated
and warm-rain type cumulonimbi contribute almost the total rainfall amount in western Japan.
These results strongly depend on the lapse rate between the low and middle levels, which is mainly
determined by the inflow of middle-level airs warmed through convective activities on the upstream
side, especially over China Continent.
Middle-level dry airs also influence the development of cumulonimbi. Much intrusion of dry
airs into cumulonimbi causes much evaporation cooling of hydrometeors and considerably
decreases the buoyancy of developing cumulonimbi, and consequently the development of
cumulonimbi is suppressed to have a middle-level CTOP. In the case of moderate intrusion of dry
airs, some cumulonimbi stop to develop at the middle level, while the others develop to a higher
altitude with maintaining their buoyancy. In such a case, two types of cumulonimbi with different
CTOPs can co-exist in the same precipitation system. Moreover, middle-level dry airs can maintain
the environmental condition under which cumulonimbi can form successively, because the intrusion
of dry airs into cumulonimbi suppress to completely stabilize the latently unstable atmospheric
condition. Therefore, the inflow of middle-level dry airs has two opposite roles on the convective
activities.
29
EFFECTS OF DUST AND BLACK CARBON ON VARIABILITY OF
THE SOUTH ASIAN MONSOON
William K. M. LAU and K. M. KIM
Laboratory for Atmospheres, NASA/Goddard Space Flight Center, Greenbelt, MD, USA
ABSTRACT
In Asian monsoon countries such as China and India, human health and safety problems
caused by air-pollution are becoming increasingly serious due to the increased loading of
atmospheric pollutants from waste gas emissions, and from rising energy demand associated with
the rapid pace of industrialization and modernization. Meanwhile, uneven distribution of monsoon
rain associated with flash flood or prolonged drought, has caused major loss of human lives, and
damages in crop and properties with devastating societal impacts on Asian countries. Historically,
air-pollution and monsoon research are treated as separate problems. However recent studies
have suggested that the two problems may be intrinsically linked and need to be studied jointly. In
this article, we will discuss fundamental physics of aerosol effects on clouds and precipitation, and
review recent modeling studies of aerosol impacts on monsoon large-scale rainfall. Specifically, we
will discuss how elevated absorbing aerosols (dust and black carbon) may interact with monsoon
dynamics to produce feedback effects on the atmospheric water cycle, which consequently affect
the monsoon circulation. We will present results showing that the large and persistent rainfall
anomalies found over northern India near the foothills of the Himalayas in the summer of 2008, may
be related to atmosphere heating by dust transported from the Pakistan, Afghanistan and the
Middle East deserts. We will also discuss how the large-scale aerosol forcing may interact with the
coupled ocean-atmosphere-land system in possible affecting the distribution of monsoon rainfall
over the Indian subcontinent.
30
ROLE OF VEGETATION IN THE MONSOON CLIMATE SYSTEM
Tetsuzo YASUNARI
Hydrospheric atmospheric Research Center (HyARC), Nagoya University,
Nagoya, Aichi 464-8601, Japan
6.
CONCLUDING REMARKS
This paper has discussed the role of land-atmosphere interaction in the Asian monsoon
system and tropical land areas. Particular emphasis and focus has been put on continental or
regional-scale soil moisture and vegetation.
Vegetation has been noted as an important variable for the formation of moist monsoon flow
over the continent, which has several functions for controlling atmospheric energy and water vapor
conditions, such as albedo, roughness, stomatal conductance and water-holding capacity of
root/soil structure. In fact, through the recent observations and modeling studies, the atmospheric
latent heating over land has been noticed fundamentally through vegetation control of
evapo-transpiration. The anthropogenically-induced change of land cover/use including the
deforestation has a great impact on regional precipitation and water cycle of the monsoon region by
changing some characteristics of vegetation control of energy and water cycle, which in turn affect
ABL and cloud/precipitation processes in regional-scale.
Finally, a general discussion has been made on how the land surface changes could induce
change of precipitation through feedback processes of moisture convergence and in-situ
evapo-transpiration processes. In this simple discussion the critical role of moisture amount near
surface and in the ABL is emphasized, to induce positive feedback to change of precipitation over
land in the monsoon region. In addition, we have emphasized that the moist land surface could play
an important role for the penetration of precipitation deep interior of the continent. This moist land
surface process has proved to be attributed essentially to the existence of vegetation. Thus, it has
strongly been suggested that the heavily vegetated land surface plays a key role for maintaining the
humid climate in the Asian monsoon region as well as in the Amazonia.
31
MULTI - SCALE FORCING OF THE TIBETAN PLATEAU AND ITS
CLIMATE IMPACTS
Guoxiong Wu1, Toshio Koike2, Yimin Liu1 and Kenji Taniguchi3
1
LASG, Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences, Beijing China
2
Department of Civil Engineering, University of Tokyo, Tokyo, Japan
3
Environmental Design, Kanazawa University, Kanazawa, Japan
The Tibetan Plateau (TP, also Qinghai-Xizang Plateau in China) extends over the area of
27- 45°N, 70- 105°E, covering a region about one quarter of the size of the Chinese territory. Its
mean elevation is more than 4000 m above sea level with the 8844 m (near 300 hPa) peak of
Mount Everest standing on its southern fringe. The mean TP altitude lies above 40% of the
atmosphere. Because of the lower air pressure, various radiation processes over the plateau,
particularly in the boundary layer, are quite distinct from those over lower-elevated regions (e.g.,
Liou and Zhou 1987, Smith and Shi 1992; Shi and Smith 1992). While the TP receives strong solar
radiation at the surface, the other parts of Asia at such a level are already in the cold middle
troposphere. Geographically the TP is located in the subtropics with westerly winds to the north and
easterlies to the south in summer, but provides a barrier to the subtropical westerly jet in winter.
Perturbations forced by the TP can generate Rossby waves in the westerlies, which can propagate
downstream and influence the circulation anomaly elsewhere. It is also located over the central and
eastern parts of the Eurasian continent, facing the Indian Ocean to the south and the Pacific Ocean
to its east. Due to its cryospheric character as well as its topographic one, the energy and water
cycles over the Tibetan Plateau possess several unique features, and can exert profound thermal
and dynamical influences on the circulation, energy and water cycles of the whole climate system.
Continuous efforts have been given to the relevant studies, and numerous results have been
obtained, as documented by Yanai and Wu (2006). Based on the newly published papers (Liu et al.,
2007; Taniguchi and Koike, 2007, 2008; Wu et al., 2007, 2008), this Chapter summarizes the recent
progresses in the studies concerning observation diagnoses, data analyses and numerical
modeling.
32
WHY CLIMATE MODELERS SHOULD WORRY ABOUT
ATMOSPHERIC AND OCEANIC WEATHER
B. KIRTMAN1 and G. A. VECCHI2
1
Center for Ocean-Land-Atmosphere Studies, Calverton, MD, USA;
2
Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA
Changing oceanic conditions, as manifest through sea surface temperature (SST), can
influence atmospheric circulation through a variety of processes, largely by changing enthalpy
fluxes across the surface. Thus, sea surface temperature (SST) anomalies play an important role in
atmospheric variability and predictability (Charney and Shukla 1981; Shukla 1998; Trenberth et al.
1998). However, atmospheric variability exists that is independent of SST forcing. Both forced and
internal aspects of atmospheric climate variability impact oceanic conditions, both through local
momentum, freshwater and enthalpy fluxes, and through the remote response of oceanic circulation
via wave modes – some these oceanic changes further impact atmospheric conditions – including
those in the monsoon regions. Describing, understanding and representing the coupled interactions
between the two fluid systems is a major focus of the scientific community, both as a source of
predictability of climate conditions around the world, on a variety of time- and space-scales, and as
a basic scientific research problem (e.g., Hendon et al 2003, Krishna Kumar et al 2005,
Krishnamurty and Kirtman 2003, Wu and Kirtman 2005, Wu et al 2006, Xie et al 2002, Kucharski et
al 2007, 2008, Annamalai et al 2003, Behera et al 2000, Huang and Kinter 2002, Song et al 2007,
Izuka et al 2000, Jin and An 1999, Kang et al 2002, Vecchi and Harrison 2000, 2002, 2004, Vecchi
et al 2006, Li et al 2002, Murtugudde and Busalacchi 1999, Murtugudde et al 2000, Nicholls 1978,
1979, Saji et al 1999, Seo et al 2007, 2008, Seo 2007, Shinoda et al 2004, Sperber and Palmer
1996, Yu et al 1999, Lau and Nath 1996, 2000, 2003, 2004, Wang and Zhang 2002, Wang et al
2003, 2004, 2005, Webster et al 1998, 1999).
Simulations of atmospheric general circulation models (AGCMs) forced by prescribed SSTs
(either observed or idealized in order to isolate particular mechanisms) allow us to assess aspects
of the SST control on climate variability, and exploit this atmospheric response to SST anomalies
for predictive purposes and to increase our understanding of the climate system. However, AGCM
experiments forced by observed SST show both consistencies with and discrepancies from
observations (e.g., Sperber and Palmer 1996; Kumar and Hoerling 1998; Kang et al. 2002; Wang et
al. 2004). In addition to fundamental predictability limitations arising directly from internal
atmospheric dynamics, two major reasons for the model-observation discrepancies are: (1) the
biases in the model physics and (2) the lack of air–sea coupling in the forced simulations. The
discrepancies due to (1) are model dependent and can be reduced with the improvement in the
representation of atmospheric physical processes in the model. The discrepancies due to (2) are
fundamental and common to all of the forced simulations, and arise because some SST features
are actually the result of atmospheric conditions that arise due to either remote SST forcing or
internal atmospheric dynamics independent of SST changes: the SST used as a forcing in some
conditions is actually a response. Using these atmospheric induced SST anomalies as a forcing on
the atmospheric model can result in improper local air–sea relationships in some regions resulting
in unrealistic atmospheric variability (Saravanan 1998; Saravanan and McWilliams 1998;
Bretherton and Battisti 2000; Wang et al. 2004, 2005; Krishna Kumar et al. 2005; Trenberth and
Shea 2005; Wu et al. 2006). Some discrepancies due to the lack of air–sea coupling have been
demonstrated in previous studies (Roebber et al. 1997; Barsugli and Battisti 1998; Wittenberg and
Anderson 1998; Wu and Kirtman 2005).
33
OCEANIC PROCESSES INFLUENCING SST IN REGIONS
RELATED TO THE ASIAN-AUSTRALIAN MONSOON SYSTEM
Bo QIU1 and Yukio MASUMOTO2
1
Dept of Oceanography, University of Hawaii, USA
Dept of Earth and Planetary Science, University of Tokyo, Japan
2
ABSTRACT
Variability associated with the Asian-Australian monsoon system has been recognized in
recent years as resulting from air-sea coupled processes. This points to the importance of ocean
dynamics that controls the time-varying sea surface temperature (SST) signals. Aside from the
surface heat flux forcing, many oceanic processes can produce changes in SST in the
Asian-Australian monsoon regions: lateral advection by oceanic mean/eddy flows, enhanced tidal
mixing in shallow seas, variability in the thermocline depth induced either locally or remotely (via
wave-guides) in the Pacific and Indian Oceans, wind-induced coastal upwelling, and salinity
stratification related to the monsoonal rainfall and river runoff. This article reviews some of these
oceanic processes on the basis of our understanding achieved in recent years.
34
TARGETED OBSERVATIONS IN DOTSTAR AND T-PARC
Chun-Chieh WU
Pacific Science Association c/o NPS Code MR/CP, Monterey, CA, USA
Email: [email protected]
ABSTRACT
Targeted observation to improve the tropical cyclone (TC) predictability is among one of the
most important research and forecasting issues for TCs. To optimize the aircraft surveillance
observations using dropwindsondes, targeted observing strategies have been developed and
examined, such as the Singular Vector, Ensemble-Transformed Kalman Filter, Ensemble Variance,
and Adjoint-Derived Sensitivity Steering Vector. The primary consideration in devising such
strategies is to identify the sensitive areas in which the assimilation of targeted observations is
expected to have the greatest influence in improving the numerical forecast, or minimizing the
forecast error.
Over the past five years, DOTSTAR (Dropwindsonde Observations for Typhoon
Surveillance near the TAiwan Region) has been one unique program to conduct targeted
observations for TCs in the North western Pacific. Up to now, 29 missions have been successfully
conducted for 25 typhoons, with 467 dropwindsondes deployed in DOTSTAR. The data have
provided useful reference information to improve the analysis and model prediction of TCS in
several major operational and research centers.
To gain more physical insights into several existing targeted techniques, studies to compare
and evaluate the techniques have been conducted to highlight the unique dynamics features in
affecting the tracks of North western Pacific typhoons. Note that the North western Pacific regions
have rather complicated dynamical systems affecting the TC motion, such as the mid-latitude
trough, the subtropical jet, the southwesterly monsoon and the binary interaction. Analyses have
been completed to identify the similarity and the difference of all these different targeted methods
and to interpret their dynamic meanings. Results from this work would not only provide better
insights into the physics of the targeted techniques, but also offer very useful information to assist
the future targeted observations, especially for DOTSTAR, Typhoon Hunting 2008 (TH08), and
Tropical Cyclone Structure 2008 (TCS-08) under the coordination of THORPEX-PARC (T-PARC), a
major WMO-sponsored international field program to study the genesis, structure change,
recurvature, targeted observation, extratropical transition of TCs in the North western Pacific during
August and September, 2008.
101
VAMOS TO THE FUTURE: CROSS-CUTTING THEMES AND
LINKS TO OTHER WCRP AND IGBP GROUPS
Hugo BERBERY1, Jose MARENGO2, Carlos EREÑO3
1
VAMOS Co-Chair, Dept. Atmospheric and Oceanic Science/ESSIC
University of Maryland, College Park, MD, USA
Email: [email protected]
2
VAMOS Co-Chair, CCST-INPE, Rodovia Dutra km, Cachoeira Paulista, São Paulo, Brazil
Email: [email protected]
3
ICPO Project Office for VAMOS, Department of Atmospheric and Oceanic Sciences,
University of Buenos Aires, Ciudad Universitaria – Pabellon II 1428, Buenos Aires, Argentina
Email: [email protected]
ABSTRACT
This presentation will summarize the activities that the Variability of the American Monsoon
System (VAMOS) Panel is carrying out to adjourn its agenda and make it more consistent with new
plans of the World Climate Research Programme (WCRP) and the International Geosphere
Biosphere program (IBGE). So far VAMOS has been constituted by three science components
addressing the following themes: (a) the South American monsoon (MESA); the North American
monsoon (NAME); and (c) the stratus clouds in the South Pacific (VOCALS). Recently, WCRP has
been taking several initiatives to update its agenda and CLIVAR has acted in response to achieve
its goals by its sunset date of 2013.
While the previous structure of three science components was extremely successful in
achieving the VAMOS objectives, VAMOS is changing its structure so that goals are more in line
and offer support to those now being proposed by WCRP and CLIVAR. During the last panel
meeting, it was decided to promote cross-cutting themes that will link the different science
components. First, one important contribution of the VAMOS/American Monsoons for the
International Monsoon Study (IMS) plans will be through its Modeling Plan, and as such it will be
promoted. Also in consonance with other WCRP activities, VAMOS has established two new
working groups or task forces, one on extremes and the other on Anthropogenic Climate Change.
Finally, a new science component has been recommended for approval to CLIVAR: The study of
the Inter Americas Seas, IASCLIP, which will investigate the role of the seas in the climate
variability of the Americas and will act as a scientific connection among all the science components
already established
One of the major contributions of VAMOS in both North and South American domains is on
the improvement of seasonal climate predictions that is made routinely at operational centers in
both monsoon regions. Data derived from past in North and South American monsoon field
campaigns have been most useful in model improvement using techniques such as data
assimilation and ensemble techniques, directed to the use of field data. This has allowed for a
better understanding of the physics and dynamics of the South and North American Monsoon
Systems (SAMS and NAMS, respectively).
Such cross cutting topics are also being contemplated in the context of other WCRP and the
IGBP programs. All of these activities have and are generating better observational knowledge and
prediction/predictability in various time scales, allowing for an accelerated transfer of knowledge to
operational centers in the region. Paleoclimate studies on SAMS show interactions with PAGES
(Past Global Changes), and SAMS studies have shown the intersection of surface biogeochemical
influences to cloud formation in the radiatively-important region of stratocumulus clouds off the
coast of Chile, as well as their influences on the physics of rainfall in SAMS due to biomass burning
from land use changes in LPB and LBA. This suggests a WCRP-IGBP intersection.
102
YEAR OF TROPICAL CONVECTION (YOTC): A JOINT WWRP
AND WCRP ACTIVITY TO ADDRESS THE CHALLENGES OF
MULTI-SCALE ORGANIZED CONVECTION
Duane WALISER
Jet Propulsion Laboratory California, Institute of Technology, Pasadena, CA
& Mitch Moncrieff National Center for Atmospheric Research, Boulder, CO
ABSTRACT
The realistic representation of tropical convection in our global atmospheric models is a
long-standing grand challenge for numerical weather prediction and climate projection. To address
this challenge, WCRP and WWRP/THORPEX have proposed a Year of coordinated observing,
modeling and forecasting of organized tropical convection and its influences on predictability. This
effort is intended to exploit the vast amounts of existing and emerging observations, the expanding
computational resources and the development of new, high-resolution modeling frameworks, with
the objective of advancing the characterization, diagnosis, modeling, parameterization and
prediction of multi-scale convective/dynamic interactions, including the two-way interaction between
tropical and extra-tropical weather/climate. This activity and its ultimate success will be based on
the coordination of a wide range of ongoing and planned international programmatic activities (e.g.,
GEWEX/CEOP/GCSS, THORPEX, EOS, AMY), strong collaboration among the operational
prediction, research laboratory and academic communities, and the construction of a
comprehensive data base consisting of satellite data, in-situ data sets and global/high-resolution
forecast and simulation model outputs relevant to tropical convection. The target time frame for
scientific focus is May 2008 to October 2009, and was chosen as a period that would leverage the
most benefit from recent investments in Earth Science infrastructure and overlapping programmatic
activities (e.g., AMY, T-PARC). Specific areas of emphasis identified in YOTC are: 1) MJO and
convectively coupled waves, 2) diurnal cycle, 3) easterly waves and tropical cyclones, 4)
tropical-extratropical interactions, and 5) monsoon. This presentation will describe the development
of this activity, its current status and planned programmatic framework and research agenda.
103
NWP RESEARCH IN SINGAPORE
Tieh-Yong KOH
School of Physical & Mathematical Sciences, Nanyang Technological University, Singapore
ABSTRACT
Natural weather hazards (e.g. floods in southern Malay Peninsula in Dec 2006),
environmental pollution (e.g. regional smoke-haze from forest fires in 1997-98) and even
longer-term climate issues (e.g. Singapore‟s ascension to the Kyoto Protocol on 11 July 2006) have
variously been featured by the news media before. So the importance of atmospheric science
research cannot be understated in this part of the world. In this presentation, research carried out
by the Tropical Atmosphere Group at Nanyang Technological University in Singapore will be
highlighted. In particular, a mesoscale NWP model, Coupled Ocean/Atmosphere Mesoscale
Prediction System (COAMPS®1), has been applied to investigate regional weather patterns. Case
studies include familiar but little understood early morning squalls and mid-afternoon thunderstorms,
as well as the rare formation of tropical cyclone Vamei in South China Sea in December 2001.
Results from an on-going project of real-time forecasts for research purposes will be demonstrated.
1
COAMPS is the registered trademark of US Naval Research Laboratory
104
SCALE INTERACTIONS IN THE TROPICS
Tim LI
IPRC and Department of Meteorology, University of Hawaii, USA
ABSTRACT
In this talk I will show our recent progress in understanding 1) the synoptic-scale feedback to
the intraseasonal oscillation (ISO), 2) the mean monsoon-ISO interaction, and 3) the feedback of
atmospheric intraseasonal and synoptic-scale variability on the El Nino-Southern Oscillation
(ENSO).
The relative contribution of intraseasonal (20-90day) and higher-frequency (HF, 2-20day)
motion (including surface wind and air-sea humidity difference variability) on the intraseasonal
surface latent heat fluxes in the global tropics is investigated using the observational data. It is
noted that the HF wind and humidity variability accounts for about 50% of the total intraseasonal
surface latent heat flux in the tropical Indian Ocean, western Pacific, eastern Pacific, and Gulf of
Mexico. This up-scale heat flux contribution is attributed to the nonlinear dependence of the heat
flux on the zonal and meridional wind components and air-sea humidity difference. The high
percentage of the intraseasonal latent heat flux contributed by the higher-frequency (2-20day)
motion implies that the synoptic-scale variability may exert a significant impact on the atmospheric
ISO through the modulation of the wind-induced surface heat exchange (WISHE). This nonlinear
up-scale feedback exhibits a strong seasonal- and geographic- dependent characteristic.
The observation shows a negative correlation between all India summer (JJAS) monsoon
rainfall and ISO intensity. It is argued that the negative correlation is primarily attributed to the
impact of the mean state of Indian summer monsoon on ISO. A strong Indian monsoon leads to the
weakening of convection over the equatorial eastern Indian Ocean. The latter may further suppress
the eastward and northward propagating ISO variances in the Indian Ocean and lead to a
weakened intraseasonal activity over the monsoon region. The ISO may feed back to the Indian
summer mean monsoon through the nonlinear eddy momentum transport.
The impacts of HF atmospheric wind variabilities on low-frequency (LF) wind stress
anomalies associated with ENSO are investigated using the daily surface wind data of the ECMWF
reanalysis from 1980 to1999. The analysis shows that there are two-way interactions between the
HF and LF variabilities. On one hand, ENSO greatly modulates the HF wind activity, with much
enhanced (suppressed) wind variability occurring during El Niño (La Niña). On the other hand, the
HF wind significantly influences the amplitude and skewness of the wind stress anomaly. Whereas
a negative skewness in the wind stress appears in the presence of the LF and the climatological
annual cycle winds, including the HF wind leads to a switch from a negative to positive wind stress
skewness. The cause of this change is primarily attributed to the ENSO-state-dependent HF wind
activity, while a random HF noise leads to a much weaker impact. The mutual interactions between
the HF and LF variabilities pose a new mechanism for understanding the El Niño and La Niña
amplitude asymmetry.
105
EFFECT OF MESOSCALE TOPOGRAPHY OVER THE TIBETAN
PLATEAU ON SUMMER MONSOON PRECIPITATION IN CHINA:
A REGIONAL MODEL STUDY
Yuqing WANG1, Xiaoying SHI2, and Xiangde XU2
1
International Pacific Research Center and Department of Meteorology, School of Ocean and Earth Science
and Technology, University of Hawaii at Manoa, Honolulu, USA
2
State Key Laboratory for Severe Weather, Chinese Academy of Meteorological Sciences, China
Meteorological Administration, Beijing, China
ABSTRACT
The effect of mesoscale topography over the Tibetan Plateau (TP) on downstream summer
precipitation in China was studied using a regional atmospheric model. Two ensemble simulations
with 30km model resolution were conducted for the 1998 summer monsoon season in China. The
standard model settings were used in the control simulation. In the sensitivity simulation, the
mesoscale feature in topography over the TP was smoothed out with the use of the 120km
resolution topography over the TP. The results show that the control simulation reproduced
reasonably well but the sensitivity simulation considerably underestimated the observed
precipitation in the Yangtze River Valley (YRV). It is found that the mesoscale feature in topography
plays an important role in generating and enhancing mesoscale disturbances over the TP. These
disturbances enhance the surface sensible heat flux over the TP and propagate eastward to
enhance convection and precipitation downstream in the YRV in China.

Corresponding author address: Dr. Yuqing Wang, IPRC/SOEST, University of Hawaii at Manoa,
1680 East-West Road, Honolulu, HI 96822. Email: [email protected]
106
THE INFLUENCE OF ENSO ON THE FREQUENCY OF EXTREME
PRECIPITATION EVENTS IN SOUTH AMERICA
Alice M. GRIMM and Renata G. TEDESCHI
Department of Physics and Post Graduate Program on Water Resources and Environmental Engineering,
Federal University of Paraná, Curitiba, Brazil
Email: [email protected]
ABSTRACT
Different phases of the El Niño – Southern Oscillation (ENSO) produce significant impacts
on monthly and seasonal precipitation over several regions of South America, as shown by
previous studies. This paper examines how El Niño (EN) and La Niña (LN) episodes modify the
frequency of extreme precipitation events in South America, and the reason for this modification.
Daily precipitation data from about 9000 stations over South America are gridded to 1.0º to
achieve more homogeneous distribution of data. Gamma distributions are fit to precipitation series
at each grid point for each day of the year, in the period 1956-2002. Daily precipitation data are then
replaced by their respective percentiles. Extreme events are those with a three-day average
percentile above 90. The number of extreme events are computed for each month of each year.
Years are classified as EN, LN, and normal years, and the mean frequency of extreme events for
each month, within each category of year, is computed. Maps of the difference (and its statistical
significance) between these mean frequencies for EN and normal years, and for LN and normal
years show that EN and LN episodes influence significantly the frequency of extreme precipitation
events in several regions of South America during certain periods.
The relationships between large-scale atmospheric perturbations and variations in the
frequency of extreme precipitation events are sought through composites of anomalous
atmospheric fields during extreme events in normal years, as well as in EN and LN episodes, in
some of the regions in which there is significant change in the frequency of these events. The
general features of those anomalous fields are similar for extreme events in any category of year
(EN, LN or normal) close to the region under focus, although they can be very different in remote
regions for different categories of years. Over the analyzed regions, the anomalous fields show the
essential ingredients for much precipitation: moisture convergence and mechanisms for lifting the
air to the condensation level. In the regions where the frequency of extreme events increases
(decreases) during EN or LN episodes the anomaly composites during extreme events in normal
years show similarity (difference) with respect to the atmospheric perturbations produced by those
episodes. This indicates that the frequency of extreme events increases (decreases) when the
large-scale perturbations favor (hamper) the circulation anomalies associated with them in those
regions.
Besides the frequency, ENSO episodes also affect the intensity of extreme events in some
regions of South America. The impact of these episodes on extreme events is even more consistent
than on monthly or seasonal precipitation totals.
Acknowledgments. This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico
(CNPq, Brazil) and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).
107
IMPACT OF SOUTHEAST INDIAN OCEAN SEA SURFACE
TEMPERATURE ANOMALIES ON MONSOON-ENSO-DIPOLE
VARIABILITY
Pascal TERRAY1, Fabrice CHAUVIN2
1
LOCEAN, Institut Pierre Simon Laplace (IPSL) Paris, France
2
Météo-France CNRM/GMGEC/UDC, Toulouse, France
ABSTRACT
Recent studies show that Indian Ocean SSTs are a highly significant precursor of transitions
of the whole monsoon-El Niño-Southern Oscillation (ENSO) system during recent decades.
However, the reasons for this specific interannual variability have not yet been identified
unequivocally from the observations.
Among these, the possibility of South-East Indian Ocean (SEIO) SST-driven variability in the
monsoon-ENSO system is investigated here by inserting positive/negative SEIO temperature
anomalies in the February‟s restart files of a state-of-the-art coupled General Circulation Model
(GCM) for 49 years of a control simulation. For each year of the control simulation, the model was
then integrated for a one year period in fully coupled mode. These experiments show that Indian
Summer Monsoon (ISM) and tropical Indian Ocean Dipole Mode (IODM) events are significantly
influenced by the SEIO temperature perturbations inserted in the mixed layer of the coupled GCM
several months before. A warm SEIO perturbation, inserted in late boreal winter, slowly propagates
northward during the following seasons, implies enhanced ISM rainfall and finally triggers a
negative IODM pattern during boreal fall in agreement with observations. A reversed evolution is
simulated for a cold SEIO perturbation. It is shown that the life cycle of the simulated SEIO signal is
driven by the positive wind-evaporation-SST, coastal upwelling and wind-thermocline-SST
feedbacks. Further diagnosis of the sensitivity experiments suggests that stronger ISM and IODM
variabilities are generated when the initial background state in the SEIO is warmer.
These modeling evidences confirm that subtropical Indian Ocean SST anomalies generated
by Mascarene high pulses during austral summer are a significant precursor of both ISM and IODM
events occurring several months later.
This finding also confirms that IODM events may be triggered by multiple factors, other than
ENSO, including subtropical SEIO SST anomalies.
108
COUPLED MODEL SIMULATIONS OF BOREAL SUMMER
INTRASEASONAL (30-50 DAY) VARIABILITY
Kenneth R. SPERBER1, H. ANNAMALAI2
1
Program for Climate Model Diagnosis and Intercomparison,
Lawrence Livermore National Laboratory, Livermore, CA, USA
Email: [email protected]
2
International Pacific Rsearch Center, University of Hawaii, Honolulu, HI, USA
ABSTRACT
Boreal summer intraseasonal (30-50 day) variability (BSISV) over the Asian monsoon
region is more complex than its boreal winter counterpart, the Madden-Julian oscillation (MJO),
since it also exhibits northward and northwestward propagating convective components near India
and over the west Pacific. Here we analyze the BSISV in the CMIP3 and two CMIP2+ coupled
ocean-atmosphere models. Though most models exhibit eastward propagation of convective
anomalies over the Indian Ocean, difficulty remains in simulating the life cycle of the BSISV, as few
represent its eastward extension into the western/central Pacific. As such, few models produce
statistically significant anomalies that comprise the northwest to southeast tilted convection which
results from the forced Rossby waves that are excited by the near-equatorial convective anomalies.
Our results indicate that it is a necessary, but not sufficient condition, that the locations the
time-mean monsoon heat sources and the easterly wind shear be simulated correctly in order for
the life cycle of the BSISV to be represented realistically.
Extreme caution is needed when using metrics, such as the pattern correlation, for
assessing the fidelity of model performance, as models with the most physically realistic BSISV do
not necessarily exhibit the highest pattern correlations with observations. Furthermore, diagnostic
latitude-time plots to evaluate the northward propagation of convection from the equator to India
and the Bay of Bengal also need to be used with caution. Here, incorrectly representing
extratropical-tropical interactions can give rise to “apparent” northward propagation when none
exists in association with the eastward propagating equatorial convection. It is necessary to use
multiple cross-checking diagnostics to demonstrate the fidelity of the simulation of the BSISV.
109
PATHWAYS TO IMPROVE THE SIMULATION AND FORECAST
OF MONSOON INTRASEASONAL OSCILLATION WITH
CONTEMPORARY GENERAL CIRCULATION MODELS
Xiouhua (Joshua) Fu
International Pacific Research Center (IPRC), SOEST, University of Hawaii, USA
Email: [email protected]
ABSTRACT
Tropical Intra-Seasonal Variability (TISV) is a fundamental building block of Asian summer
monsoon. The associated intraseasonal wet and dry spells strongly modulate the weather systems,
thus the socio-economic activities (e.g., agriculture, water management et al.) in this World's most
populous region. This area is also one of the most vulnerable areas around the world with respect
to the impacts of climate-related natural disasters. About 80 percent of these natural disasters are
caused by extreme hydro-meteorological events, which are strongly modulated by the TISV. To
develop a capability in forecasting TISV with lead time beyond two weeks is extremely desirable.
Unfortunately, many state-of-the-art general circulation models (GCMs) still have various
problems to reasonably simulate TISV. Under real forecast context (e.g., Seo et al. 2005), the
predictability of TISV is only about a week by simply extending conventional weather forecast with
longer integration. This study aims to address two relevant questions: 1) what are the critical pieces
of model physics for the realistic simulation of TISV that have been missed or misrepresented in
many contemporary GCMs? 2) In what degree is the TISV predictability affected by different
settings of initial and boundary conditions?
To address the first question, a suite of sensitivity experiments has been carried out under a
weather forecast mode and with three 20-year free integrations with ECHAM-4 and a coupled
version. It was found that a robust TISV can be sustained in the model only when the model
produces a significant proportion ( 30%) of stratiform rainfall for both the forecast experiments and
long-term free integrations. When the stratiform rainfall proportion becomes small, the tropical
rainfall in the model is dominated by high-frequency disturbances with neither eastward propagating
nor northward-propagating TISV being sustained. This result suggests that the representation of
stratiform rainfall and its connections with convective component in contemporary GCMs is
probably a critical issue needed to be seriously reconsidered, in order to have overall success in the
simulation and prediction of TISV. To address the second question, a series of TISV forecast
experiments has been conducted under different initial and boundary conditions. Their impacts on
the TISV forecast skill is under examination and will be reported in the coming meeting.
110
PREDICTION AND PREDICTABILITY OF SOUTH ASIAN
MONSOON IN COUPLED MODELS ON INTRASEASONAL
TIMESCALE
V. KRISHNAMURTHY1, Emilia K. JIN2
1
Center for Ocean-Land-Atmosphere Studies, IGES, Calverton, MD, USA
E-Mail: [email protected]
2
Department of Climate Dynamics, George Mason University, Fairfax, VA, USA
ABSTRACT
The daily predictions of monsoon rainfall over the South Asian monsoon region by ten
coupled general circulation models (CGCMs) from the DEMETER (Development of a European
multimodel ensemble system for seasonal to interannual prediction) and APCC/CliPAS (APEC
Climate Center/Climate Prediction and Application to Society) projects are assessed. The
predictability of the models is also evaluated on intraseasonal timescale. The prediction skill and the
predictability are determined by decomposing the daily rainfall from the DEMETER and CliPAS
hindcast integrations using multi-channel singular spectrum analysis (MSSA). The dominant MSSA
modes of these models consist of an oscillatory mode at 45-day timescale and a persistent mode
that is strongly related to the sea surface temperatures of the Pacific and Indian Oceans. The error
growths of these components are evaluated with respect to similar components of the observed
rainfall data in order to assess the forecast skill and predictability of the CGCMs. The ability of the
models to predict the active and break cycles on timescales larger than synoptic scale will be
discussed. The relative roles of intraseasonal component and persistent component in determining
the predictability of seasonal mean monsoon rainfall will also be presented.
111
POTENTIAL FOR PREDICTABILITY OF THE INDIAN MONSOON
INTRASEASONAL VARIABILITY IN A REGIONALLY COUPLED
ATMOSPHERE–MIXED-LAYER-OCEAN MODEL
Nicholas P. KLINGAMAN, Hilary WELLER, Julia M. SLINGO,
Steve J. WOOLNOUGH, Peter M. INNESS
Walker Institute for Climate System Research and Department of Meteorology,
University of Reading, UK
ABSTRACT
Recent studies of tropical intraseasonal variability in coupled models have strongly
suggested the need for fine ocean vertical resolution and diurnal coupling, in order to accurately
represent the intraseasonal variability of sea-surface temperatures (SSTs). The authors have
previously demonstrated that SST variability on timescales as short as one day is necessary to
reproduce intraseasonal power in Indian summer monsoon rainfall consistent with observations. In
the present study, we examine the northward-propagating intraseasonal oscillation (NPISO) of the
Indian monsoon in a high-resolution regionally coupled atmosphere–mixed-layer-ocean model,
HadKPP. HadKPP consists of the Hadley Centre atmosphere model (HadAM3) coupled to the K
Profile Parameterization (KPP) mixed-layer model. KPP has a vertical resolution of about 1
m through the top 50 m of the ocean; the models are coupled every 3 hours. Four-dimensionally
varying temperature corrections strongly reduce the monthly-mean ocean temperature bias. A
30-member ensemble of HadKPP simulations reproduces an amount of intraseasonal power in
rainfall in-line with both observations and previous HadAM3 simulations forced by high-frequency
observed SSTs. The phase relationship between rainfall and SST is similar to observations, as well
as to previous coupled-model studies. When composite active and break events are constructed,
HadKPP generates SST anomalies in the Bay of Bengal and the Arabian Sea that are nearly equal
to composites generated from observations by the Tropical Rainfall Measuring Mission Microwave
Imager (TMI). While the active (break) composite also contains the previous break (active) event,
the model fails to consistently generate the following break (active) event, which may be due to
deficiencies in the HadAM3 convective parameterization. These simulations demonstrate that the
computationally efficient KPP mixed-layer model has the potential to improve extended-range
predictability of monsoon intraseasonal variability.
112
RESPONSE OF THE SOUTH ASIAN SUMMER MONSOON TO
GLOBAL WARMING: MEAN AND SYNOPTIC SYSTEMS
H. ANNAMALAI, Markus STOWASSER, and Jan HAFNER
International Pacific Research Center (IPRC), University of Hawaii, Honolulu, Hawaii, USA
Email: [email protected]
ABSTRACT
Recent diagnostics with the GFDL_CM2.1 coupled model‟s 20th century simulations reveal
that this particular model demonstrates skill in capturing the mean and variability associated with
the South Asian summer monsoon precipitation. Motivated by this, we examine the future
projections of the mean monsoon and synoptic systems in this model simulations in which
quadrupling of CO2 concentrations are imposed.
In a warmer climate, despite a weakened cross-equatorial flow, the time-mean precipitation
over peninsular parts of India increases by about 10-15%. This paradox is interpreted as follows:
The increased precipitation over the equatorial western Pacific forces an anomalous descending
circulation over the eastern equatorial Indian Ocean, the two regions being connected by an
over-turning mass circulation. The spatially well-organized anomalous precipitation over the eastern
equatorial Indian Ocean forces twin anticyclones as a Rossby-wave response in the lower
troposphere. The southern component of the anticyclone opposes and weakens the climatological
cross-equatorial monsoon flow thereby limiting the coastal upwelling along Somalia. That, together
with the patch of easterly anomalies in the southern Arabian Sea result in local sea surface warming
and evaporation becomes a local maximum over the southern Arabian Sea. It is shown that
changes in SST are predominantly responsible for the increase in evaporation over southern
Arabian Sea. Our diagnostics suggest that in addition to the increased CO 2-induced rise in
temperature, evaporation, and atmospheric moisture, local circulation changes in the monsoon
region further increases SST, evaporation, and atmospheric moisture leading to increased rainfall
over peninsular parts of India. This result implies that accurate observation of SST and surface
fluxes over the Indian Ocean are of urgent need to understand and monitor the response of the
monsoon in a warming climate.
To understand the regional features of the rainfall changes, the IPRC Regional Climate
Model (RegCM), with three different resolution settings (0.5 x 0.5, 0.75 x 0.75 and 1.0 x 1.0 degree),
was integrated for 20 years, with lateral and lower boundary conditions taken from the GFDL model.
The RegCM solutions confirm the major results obtained from the GFDL model but also capture the
orographic nature of monsoon precipitation and regional circulation changes more realistically. The
hypothesis that in a warmer climate, increase in troposphere moisture content favor more intense
monsoon depressions is tested. The GFDL model does not reveal any changes, but solutions from
the RegCM suggest a statistically significant increase in the number of storms that have wind
speeds of 15-20 ms-1 or greater, depending on the resolution employed. Based on this regional
model solutions a possible implication is that in a CO2 richer climate an increase in the number of
flood days over central India can be expected. The model results obtained here, though plausible,
need to be taken with caution since even in this “best” model systematic errors still exist in
simulating some aspects of the tropical and monsoon climates.
113
HISTORIC AND FUTURE CHANGES IN EXTREME RAINFALL
INDICES OVER MONSOON REGIONS BY IPCC AR4 MODELS
Cheng-Ta CHEN
Pacific Science Association c/o NPS Code MR/CP, Monterey, CA, USA
ABSTRACT
Changes in the frequency or intensify of extreme weather and climate events could have
profound impacts on both human society and the natural environment. Indicators based on the
observed daily precipitation during the second half of the 20th century suggest that, on average, the
world has become wetter, and wet spells produce significant higher rainfall totals now than a few
decades ago.
It is of great interest to evaluate the ability of the current generation of climate models to
simulate observed extreme rainfall distributions and their trends. But the lack of comparable
long-term global gridded daily observations often leads to a deferral of model evaluation or limited
evaluation of only the mean precipitation climatology. Additional difficulties arise from the scaling
issue when comparing the extreme events among the observation and models with different spatial
resolution. The interpretation of model output as point estimate vs. areal mean and the spatial
interpolation schemes both can have strong impact on the outcome of validation and comparison.
With appropriate consideration of the spatial scale of the observed and simulated data, the
present-climate extreme precipitation events simulated by IPCC AR4 climate models are evaluated.
For various monsoon regions, the daily extreme rainfall distribution is reasonably simulated. The
common model bias is the reduction of spatial variability (underestimate in higher extremes and
overestimate in area where daily extreme rainfall is small). The bias resembles to the systematic
error in the annual mean precipitation simulation. The model simulations for the past trends in the
extreme precipitation over the 1961-2000 period are inconsistent with observation and no common
features found among different models. Model ensemble mean projections for the 2081-2100
period show that, except subtropical arid region, extreme daily rainfall almost increase everywhere
with larger percentage increase in the tropics. With the model reliability information, the common
characteristics of future projection of simulated changes in extreme precipitation from IPCC AR4
models and their uncertainties will be assessed. Probabilistic projection of future change provides
model uncertainty information to the impact studies and risk-decision analysis should be
encouraged.
114
CLIMATE CHANGE AND DECADAL VARIABILITY OF THE EAST
ASIAN SUMMER MONSOON: A MODELING STUDY
Yonghui LEI, Brian HOSKINS, Julia SLINGO and Andrew TURNER
National Centre for Atmospheric Science and Department of Meteorology,
Walker Institute for Climate System Research, University of Reading, UK
ABSTRACT
Much of China‟s rainfall derives from the East Asian Summer Monsoon (EASM), and we
now know that over at least the last 50 years, the monsoon has displayed substantial decadal
variations which have had major impacts on the distribution of rainfall across the country. A major
challenge is determining how the interplay between natural decadal variations and anthropogenic
climate change will shape the future distribution of rainfall across the country, along with possible
changes in frequency and intensity.
In this paper we present the results of an analysis of a multi-century simulation with the
Hadley Centre‟s coupled climate model to explore whether decadal variability of the EASM is a
naturally occurring phenomenon and what its potential drivers are. We then use century long
simulations with double CO2 concentrations to investigate the impact of global warming on the
EASM and whether decadal variability is changed in pattern and/or amplitude. Finally, we draw
some conclusions about the implications of the results for future climate scenarios for China.
115
THE INFLUENCE OF MONSOON ON THE PRECIPITATION
JUMP IN THE SAHEL
W. Timothy LIU, Xiaosu XIE, and Kristina B. KATSAROS*
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
ABSTRACT
The socioeconomic vulnerability of the agricultural societies in the Sahel region of West
Africa to the vagary of summer rainfall has received world recognizance. The recently initiated
international endeavor of the African Monsoon Multidicispline Analysis underscores the
fundamental gaps in our knowledge of the coupled atmosphere-ocean-land system in this region
and the large systematic errors in dynamical models used for prediction. We have developed and
validated a method to estimate the moisture transport integrated over the depth of the atmosphere
(IMT), using ocean surface wind vector from the scatterometer QuikSCAT, cloud-drift winds from
NOAA, and the integrated water vapor from the Special Sensor Microwave Radiometer. Nine years
(1999-2008) of IMT and rainfall from the Tropical Rain Measuring Mission (TRMM) are used in this
study.
TRMM data show a rather abrupt transition of rainfall at 8°N. Rainfall peaks in June south of
this latitude, but in August north of this latitude. The annual cycle of rainfall in the southern region
near the Gulf of Guinea (GG) is found to be in phase with meridional IMT from GG, peaking in June.
Many studies have postulated that the rainfall in northern region (Sahel) is controlled by
high-frequency events in the westward propagating Easterly Waves (EW), but there is no clear
evidence of phase coherence between rainfall and EW in annual and interannual variations. We
observed IMT coming onshore from the Atlantic in the west lags those coming from the Gulf of
Guinea in the south by two months, with peak in August. The IMT from the Atlantic has significantly
high contemporary correlation with rainfall in the Sahel region but not with rainfall in regions near
the Gulf of Guinea. On contrary the northward IMT from Gulf of Guinea has strong correlation with
rain just north of GG but not the rainfall further north. While the IMT from the Atlantic is positive
(onshore) only for the three summer months (July, August, and September), and strongest in
August, the surface wind are positive for a much longer period with no strong peak in August. The
implication is that the onshore moisture transport from the Atlantic is confined to the surface with off
shore transport aloft, except for three summer months. During the August, the on shore transport
extends far up in the troposphere fueling moisture and instability for heaviest rainfall in the Sahel.
This fact has been missed by most of the past analysis. The rainfall jump may be the result of the
phase difference between the IMT from the Atlantic and the GG.
The interannual anomalies of rainfall in the Sahel region is positively correlated with IMT
from the Atlantic, but not with IMT from the GG. The anomalous wet season in 1999 is caused by
the eastward anomalies of IMT from the Atlantic and the anomalous dry summer of 2005 is
associated with westward anomalies of IMT over the Atlantic.
*Permanent address; PO Box 772, Freeland, WA 98249, USA
116
ON THE DYNAMICAL PREDICTABILITY OF THE INDIAN
SUMMER MONSOON DEPRESSIONS
Yi-Chi WANG and Wen-wen TUNG
Department of Earth and Atmospheric Sciences, Purdue University
West Lafayette, Indiana USA
Email: [email protected]
ABSTRACT
As one of the prominent features of the South Asian Monsoon, monsoon depressions
usually brings great amount of rainfall causing fatal damage along its path. In order to quantify the
dynamical predictability of the monsoon depressions, the depressions originated in the Bay of
Bengal during August 2006 were studied with satellite imagery, radiosonde observations, global
reanalysis and meso-scale model simulations. Four monsoon depressions formed and traversed
India in August 2006. These depressions evolved similarly after their geneses over the northern
Bay of Bengal, as confirmed by the precipitation observed by the Tropical Rainfall Measuring
Mission (TRMM 3B42) and in the NCEP/NCAR reanalysis. The event during August 2--5, 2006, is
then extensively examined and simulated using the Advanced Research Weather Research &
Forecasting model (ARW). The model has a two-domain two-way nesting setup. The outer domain,
with 30-km resolution, covers the entire India, the Bay of Bengal, parts of the Arabian Sea, parts of
the South East Asia, and the Tibetan Plateau. With 10-km resolution, the inner domain allows the
convective organization of the depression over India and the Bay of Bengal to be resolved.
Boundary conditions and initial conditions are interpolated by the WRF Preprocessing System(WPS)
with Final(FNL) global analysis and the NCEP Sea Surface Temperature(SST) analysis.
Preliminary ARW model experiments were conducted with various physical
parameterizations provided by ARW, e.g. cumulus, and land-surface parameterizations. It is found
that in all experiments the model fails to reproduce several characteristics of the evolution of the
depression. Within the first few days of genesis, the location of the low pressure center at the
surface is close to what observed. However, the model tends to over-estimate rainfall and misplace
major precipitating areas associated with the depression. Moreover, 3 days after formation(Aug 5),
the depression in the ARW model remains stagnant near 21 N and 81 E and intensifies, while in
observations it moves further westward inland and gradually weakens. To further investigate the
factors affecting the track and intensity of the depressions, ensemble experiments are being
conducted to examine the model's sensitivity to initial conditions. The model's dynamical predictive
utility of the depressions can then be quantified.
117
IMPACT OF EAST ASIAN SUMMER MONSOON ON SEASONAL
VARIATIONS OF AEROSOLS OVER EASTERN CHINA
Jianping LI1, Li ZHANG1, 3, and Hong LIAO2
1
2
LASG, Institute of Atmosphere Physics (IAP), Chinese Academy of Sciences (CAS), Beijing, China
LAPC, Institute of Atmosphere Physics (IAP), Chinese Academy of Sciences (CAS), Beijing China
3
Graduate University of Chinese Academy of Sciences, Beijing, China
ABSTRACT
Ground measurements show that seasonal variations of aerosols in Eastern China are
different from those in the Eastern United States; while aerosol concentrations are the highest in
winter over Eastern China, they are the highest in summer in the Eastern United States. We apply a
global 3-D chemical transport model (GEOS-CHEM) driven by NASA/GEOS assimilated
meteorological data to quantify the roles of East Asian summer monsoon and seasonal variations of
emissions of aerosols/aerosol precursors in influencing seasonal variations of sulfate, nitrate,
ammonium, black carbon and organic carbon aerosols in Eastern China. Model results show that
East Asian summer monsoon plays a major role in determining seasonal variations of aerosols in
Eastern China. Rainfall associated with summer monsoon leads to large wet deposition of aerosols,
and the cross-equatorial flows (45º -100º E) from the Southern Hemisphere bring clean and wet air
to Eastern China, all contributing to the low concentrations of aerosols in summer. Sensitivity
studies with no seasonal variations in emissions indicate that East Asian summer monsoon can
reduce aerosol concentration averaged over the domain of 110º -120º E and 20º -45º N by 60-70%,
as the averaged surface-layer aerosol concentration in July is compared with that in January. We
also examine the influence of East Asian monsoon on transport and distributions of aerosols in the
free troposphere. Results might have important implications for understanding variation of air
quality and climate effects of aerosols in Eastern China.
Key words: East Asian summer monsoon, Aerosol, Chemical transport model
118
SNOW-MONSOON TELECONNECTIONS: TESTING
COMPETING MECHANISMS USING IDEALIZED SNOW
FORCING IN THE HADLEY CENTRE MODEL
Andrew TURNER and Julia SLINGO
National Centre for Atmospheric Science, Walker Institute for Climate System Research,
University of Reading, UK
ABSTRACT
Anomalous snow cover in the previous winter/spring has long been regarded as a possible
predictor for the Asian summer monsoon. However the literature in this area is inconclusive, both in
the mechanism that communicates snow anomalies to the monsoon summer, and even the region
from which snow has the most impact. Interactions with ENSO further complicate our
understanding.
A 1050-year control integration of the HadCM3 coupled model is analysed and shows
evidence for weakened monsoons being preceded by strong snow forcing over either the
Himalaya/Tibetan Plateau, or West Eurasia. However, EOF analysis of springtime interannual
variability in snow cover shows the leading mode to have opposite signs in these regions. Hence
competing mechanisms are likely.
Ensemble integrations are carried out using the atmospheric component of HadCM3 and a
variety of anomalous snow forcing initial conditions obtained from the control integration. The
application of climatological SSTs ensures the absence of any ENSO effects. This study presents
results from these experiments.
119
FIFTY YEARS CLIMATE VARIABILITY IN GUINEA
Alpha Boubacar BARRY, Aliou DIALLO and Aboubacar DIALLO
Direction Nationale de la Météorologie de Guinée, BP 566 Conakry
E-Mail: [email protected]
ABSTRACT
Guinea situated in the costal region of West Africa has its climate characterized by a two
seasons. They are under meanly two air fluxes: Northeasterly during the dry season and the
monsoon wind in wet period. The country itself is the source of many rivers, including regional wide
dimension (Niger, Senegal, Gambia, Mano rivers etc...).The run-off of the rivers is fully benefiting
from the rainfall regime, mainly from monsoon, which occurs from April to October. In this study
rainfall, temperatures and evaporation for the period 1931 to 2005 and for 20 climatic stations are
used. By this analysis it will be possible to know the climate evolution in Guinea and detect the
natural variability and the Climate Change, which occurred itself. All this is to attract the attention of
the decision makers on the Climate Change.
EVOLUTION DU CLIMAT EN GUINEE AU COURS DES
CINQUANTE DERNIERES ANNEES
La Guinée, située sur la côte Ouest de l‟Afrique est soumise à l‟influence de 2 saisons
dominées par le flux d‟harmattan du nord pendant la saison sèche et le flux de mousson pendant la
saison pluvieuse. C‟est le château d‟eau de l‟Afrique de l‟ouest à cause des grands fleuves
internationaux (Niger, Sénégal, Gambie, Mano,…) qui y prennent naissance. Ces cours d‟eau sont
alimentées à travers d‟intenses et continues pluies de mousson (entre 1500 et 5000mm)
enregistrées principalement d‟Avril à Octobre.
Dans cette étude, à travers l‟analyse de la pluviométrie, des températures et de
l‟évaporation entre 1931 et 2005 pour une vingtaine de stations climatiques, nous allons montré
comment le climat à évoluer en Guinée en dégageant la variabilité naturelle et le changement
climatique intervenu. Notre objectif final étant d‟attirer l‟attention des décideurs sur l‟impact du
changement climatique attendu.
120
THE ROLE OF CONTINENTAL-SCALE LANDMASS IN
MONSOONAL AND GLOBAL PRECIPITATION DISTRIBUTION
Winston C. CHAO
NASA/Goddard Space Flight Center
ABSTRACT
It was argued by Chao and Chen (2001) that land-sea thermal contrast on the continental
scale is not a necessary condition for monsoons and that a monsoon is an ITCZ that have moved
into the subtropics in its annual cycle of latitudinal movement. Chao and Chen supported their
contention by GCM experiments in which they replaced landmass by ocean and were able to
generate monsoons. However, land-sea thermal contrast does exist and must play a role in
monsoonal rainfall distribution. Land-sea thermal contrast is one facet of continental-scale
landmass. In this article the roles of land-sea thermal contrast in monsoonal rainfall distribution and
in middle latitude storm tracks are examined through GCM experiments. Comparison of a set of two
GCM experiments in which the sea surface temperature (SST) from observations is prescribed from
observations with and without a six-month delay reveals the role of land-sea thermal contrast.
These experiments confirm that land-sea thermal contrast is not a necessary condition for
monsoons and that a monsoon should be viewed as an ITCZ displaced into the subtropics, instead
of a continent-sized giant sea breeze. However, land-sea thermal contrast does have influence on
the distribution of monsoonal rainfall. The temperature rise over south Asia as the season moves
into summer helps the Asian monsoon to start early. However, this role is not the same as that of
the land-sea thermal contrast as in the conventional explanation for the cause of monsoon. The
heated landmass in summer contributes to the displacement of ITCZ into the subtropics. Also, the
heated landmass in summer, by drawing moisture toward itself, limits the range of the summer
storm tracks in the middle latitude oceans. On the other hand, in winter the landmass does not
present a competition for rainfall and thus allow middle latitude storm tracks to expand over the
ocean.
121
TORRENTIAL RAINFALL CAUSED BY INTERACTIONS OF TC
AND SOUTHWESTERLY FLOWS
Jau-Ming CHEN, Ching-Feng SHIH, Chung-Yi HSU
Pacific Science Association c/o Code MR/CP Naval Postgraduate School Monterey, California, USA
ABSTRACT
This study aims at analyzing the interaction processes between tropical cyclone (TC) and
southwesterly flows responsible for torrential rainfall in Taiwan during the July-September season.
The analysis focuses on the multiple-timescale interactions between the intraseasonal and synoptic
modes. Major findings in this study are as follows:

Torrential rainfall resulted from the TC-southwesterly flow interactions is concurrent with
low-level circulation anomalies featuring an anomalous low to the north of Taiwan and an
east-west elongated anomalous high to the south. This circulation pair induces strong
anomalous westerly and southwesterly flows from the South China Sea into Taiwan, leading to
intense moisture supplies and rainfall activities right after the passage of TC across Taiwan.

This anomalous pair is a result of joint effects from intraseasonal (30-60-day and 10-24-day
modes) and synoptic (2-7-day mode) modes. Among them, the 30-60-day mode is the major
component to maintain the anomalous southwesterly flows. The 10-24-day mode induces
anomalous westerlies from Asian continent into Taiwan which is dry in nature. The 2-7-day
mode mainly reflects the movement of TC itself.

The 30-60-day mode emanates from the tropics, moves northward, and reaches the maximum
phase near Taiwan during the period of TC passage. It migrates 1 degree/day after the TC
passage and thus forces continuous water transport from the South China Sea into Taiwan via
anomalous southwesterly flows, maintaining torrential rainfall in Taiwan for several days after
the TC passage.
------------------------------------------------------------------------------------------------------Corresponding Author: Dr. Jau-Ming Chen, [email protected],TEL: 886-7-571-5421, Fax: 886-7-571-7301,
rd
No. 482, Jhongjhou 3 Rd., Kaohsiung, 805, Taiwan
122
DIURNAL RAINFALL OVER SOUTHEAST CHINA AND ITS
RELATION WITH THE DIURNAL VARIATION OF MONSOON
FLOW
Guixing CHEN, Weiming SHA and Iwasaki TOSHIKI
Department of Geophysics, Graduate School of Sci., Tohoku Univ., Sendai, Japan
E-mail: [email protected]
ABSTRACT
Further studies on the diurnal variation are needed to forward our understanding on the
monsoon precipitation systems and to improve the performance of numerical models on the diurnal
cycles in monsoon regions. The Southeast China (SEC), due to its unique location, is an ideal place
to study the diurnal variation of monsoon and its impacts. The motivation of present work is to clarify
the relationship between the diurnal variation of monsoon flow and the diurnal rainfall.
To obtain a full view, the present study examines the spatial patterns and diurnal cycles over
SEC using the satellite-derived rainfall with high resolution. Our results show that diurnal variability
is weak in spring, while it becomes evident since presummer. Morning rainfall is found to dominate
the South China offshore. And nocturnal or near-dawn rain is prevalent at the east flank of plateaus.
However, the two-peak rainfall is observed over the Central Eastern China, with morning
(earlyafternoon) rain over the valleys and plains (mountains and lees). In midsummer, a
sandwiched distribution of diurnal patterns appears over the Mainland China, as expected from the
intense surface heating and local circulation.
It is found that, this nocturnal acceleration of low-level wind becomes dominant since
pre-summer when the monsoon flow becomes active. The diurnal maxima of monsoon flow mainly
develops in response to the impacts of elevated landmass and boundary process. And it turns to
regulate the warm and moist inflow that feeds to the frontal zone over SEC. In early morning,
enhancement of frontgenesis and convective instability is likely favorable for the meso-scale
organized convections with prolong duration. Consequently, the interaction between the diurnal
variation of monsoon flow and the frontal zone can produce more rainfall in the morning over SEC.
Based on the non-hydrostatic model, numerical simulations on a heavy rain case are to verify the
possible monsoon-front interaction that may regulate the diurnal rainfall over SEC.
123
EFFECTS OF INCREASED CO2 CONCENTRATION ON
MONSOON CIRCULATIONS
Annalisa CHERCHI, Simona MASINA, and Antonio NAVARRA
Centro Euromediterraneo per i Cambiamenti Climatici, and Istituto Nazionale di Geofisica e Vulcanologia,
Bologna Italy
Email: [email protected]
ABSTRACT
The mean circulation and variability of the Indian summer monsoon (ISM) and of the West
African monsoon (WAM) are studied by means of 20th century coupled model simulations. ISM and
WAM are examples of monsoon circulations driven by land-sea thermal contrast and they are
largely influenced by air-sea feedbacks, hence the analysis is focused on the role of the adjacent
oceans to the intensity and variability of the monsoon precipitation. Another focus is dedicated to
the changes in the monsoon intensity and variability simulated in a warmer climate, where both
mean rainfall and interannual variability should strengthen, using 21st century scenarios and
experiments forced with higher than present concentration of carbon dioxide. Modified land-sea
thermal contrast and moisture abundance will be investigated through an analysis of the feedbacks
and dynamical process of the warmer climate. A recent analysis of a set of experiments with CO 2
multiplied by a factor of 2, 4 and 16 with respect to present-day value revealed a non-linear
response of the climate sensitivity to increased CO2 concentration, and extreme CO2 conditions
suggested the possibility of permanent warm conditions in the tropical Pacific Ocean similar to the
peak of El Nino. The effects on the monsoon circulations of these extreme forcing conditions is
compared with the changes simulated in the 21st century scenarios, where the variability in the
Pacific sector seems almost unchanged.
124
ASSESSMENT OF GCM-BASED RAINFALL SIMULATIONS FOR
THE AUSTRAL-INDONESIAN REGION
Akhmad FAQIH1, Joachim RIBBE2, Holger MEINKE3
1
E-mail: [email protected]
Department of Biological and Physical Sciences, Faculty of Sciences, University of Southern Queenslan,
Toowoomba, Queensland 4350, Australia
3
Crop and Weed Ecology, Department of Plant Sciences, Wageningen University, PO Box 430, 6700 AK
Wageningen, The Netherlands
2
ABSTRACT
We evaluated the performance of rainfall simulations over the Austral-Indonesian region by
the 21 GCMs that were included in the fourth assessment report (IPCC AR4, 2007). For this we
used monthly data of historical and future rainfall simulated by these models. We assessed
seasonal time series and climatology of the 20th century rainfall simulations by calculating
departures from observed rainfall. For this purpose we developed a quantitative assessment tool
based on cumulative distribution function (CDF) and Kolmogorov-Smirnov (KS) tests. Our
assessment shows considerable discrepancies between observed and simulated rainfall amongst
the 21 models. Generally, the representation of rainfall is better for northern Australia during
seasonally dry periods (Austral winter and spring). Over 80% of the models overestimate seasonal
rainfall by 4 to 8 mm/day/season for northern Indonesia in summer. For other seasons more than
50% of the models reproduce unrealistic rainfall distributions, particularly due to overestimation of
rainfall in the Indonesian region. To rank the models, we use cumulative absolute difference (CAD)
calculated for average seasonal (CADS) and all seasons rainfall series (CADг2). A small CAD value
indicates a better model performance. The CADS shows that MIUB-ECHO-G model has the lowest
deviation from recorded seasonal rainfall in summer and winter (5,057 and 3,721 mm/day/season
respectively), while MRI-CGCM2.3.2a performs best during transition periods in autumn and spring
(4,467 and 3,799 mm/day/season, respectively). The late 21st century rainfall assessments of
these two models indicate considerable rainfall changes particularly over Indonesia for all seasons.
Rainfall projections for northern Australia, however, show little changes in rainfall patterns.
Structural differences between these two models and other GCMs need to be investigated to
pinpoint the physical causes of differences in performance.
2
s
n
CADT  
i 1 j 1
AD where AD = cumulative absolute maximum difference (mm) between
ij
simulated and observed seasonal rainfall from 1979 to 1999 periods at grid point j (n = 104) in season
i (s=4).
125
INTERDECADAL VARIABILITY OF REGIONAL SEA SURFACE
TEMPERATURE AND RAINFALL IN THE
AUSTRAL-INDONESIAN REGION
Akhmad FAQIH1, Joachim RIBBE2, Holger MEINKE3
1
E-mail: [email protected]
Department of Biological and Physical Sciences, Faculty of Sciences, University of Southern Queenslan,
Toowoomba, Queensland 4350, Australia
3
Crop and Weed Ecology, Department of Plant Sciences, Wageningen University, PO Box 430, 6700 AK
Wageningen, The Netherlands
2
ABSTRACT
We conducted a study of regional sea surface temperature variability in the
Austral-Indonesian region and their role in driving rainfall on decadal time scale. For this we used
observed SST data from the UK Hadley Centre known as HadISST 1.1 in our analysis. The results
of empirical orthogonal function (EOF) analysis of the seasonal SST data are dominated by
spatio-temporal patterns that characterise the seasonal meridional pattern. This pattern correlates
significantly with terrestrial rainfall in the region. The SST data also indicates a zonal pattern
between western and eastern part of the region. The western region corresponds to the South
China Sea and the Eastern Indian Ocean. The eastern region is connected to the Western West
Pacific region and the local sea between Indonesia and northern Australia. These also correlate
significantly with the rainfall over some areas in the region. The spectral analysis demonstrates
interdecadal variability in the regional SST that might be linked with the Pacific inter-Decadal
Oscillation (PDO). Climate shifts related to different PDO phases are apparent in the SST data and
can be linked to changes in rainfall. Considerable upward trends of the regional SST in different
areas in the Austral-Indonesian region are also found, particularly after 1980s. It is possible that
climate change might have a major role in contributing to these trends. The increase of mean SST
anomalies on decadal timescales could lead to more active ocean-atmosphere processes. These
might cause an increase of more extreme rainfall events on higher frequency time scales.
126
THE SUMMER ASIAN MONSOON OLR INDICES
OPERATIONALLY MONITORED IN JMA
Norihisa FUJIKAWA
Climate Prediction Division, Japan Meteorological Agency
Email: [email protected]
ABSTRACT
Large crowds of cumulonimbus in the Asian summer monsoon region have great influence
on general atmospheric circulation as a heat source. Their activities are closely related to the
summer climate not only in the subtropical monsoon region but also in the middle latitudes
especially around Japan. To monitor the activity of Asian summer monsoon, the All Indian Summer
Rainfall Index (Parasatharathy 1994) and the Webster and Yang Index (hereafter WYI, Webster
and Yang 1992) which is the vertical shear of zonal wind over south Asia have been used by
researchers. JMA also proposed the Summer Asian Monsoon OLR Indices (SAMOIs), which have
been monitored in the Monthly Report on Climate System since 1997.
SAMOIs are calculated from OLR (provided by NOAA) consisting of three indices which
represent the degree of the total activity (SAMOI-A), the northward shift (SAMOI-N) and the
westward shift (SAMOI-W). As we began to monitor SAMOIs in 1997, we confirmed the relationship
between each SAMOI and the atmospheric circulations. The results showed that SAMOI-A had a
good relationship with the meridional shift of the subtropical jet, the strength of the Tibetan high, low
level circulation anomalies known as the Pacific-Japan teleconnection pattern and the development
of the barotropic anticyclone around Japan. In the last connection, we found the high correlation
(the correlation coefficient was +0.77) between SAMOI-A and the seasonal (JJA) mean
temperature in northern Japan.
After we began to monitor SAMOIs, some indices for featuring the Asian summer monsoon
activity such as the Monsoon Hadley circulation Index (Goswami et al. 1999) and the Meridional
Thickness Index (hereafter MTI, Kawamura 1998) were proposed. Then Wang and Fan (1999) also
proposed MCI1 and MCI2 as a result of an intercomparison among these indices. Meanwhile, the
Japanese 25-year Reanalysis Project (JRA-25) was completed in 2006. So we reconfirmed the
relationship between SAMOI-A and the atmospheric circulations using longer and higher quality
dataset and intercompared these indices. In this presentation, we will focus on three indices,
SAMOI-A, WYI and MTI which feature the whole Asian summer monsoon activities.
The cross-correlations among three indices are very high and the global scale distributions
of correlation coefficients between each index and the atmospheric circulations show similar
patterns. However their characteristics in the distributions of correlation coefficients are different in
the details. For example, WYI and MTI show a clear ENSO-related pattern while SAMOI-A has only
a weak ENSO signal. This indicates that convective activities accompanied by the Asian summer
monsoon are affected by not only the global-scale circulations but also the continental-scale
circulations and boundary conditions. Over Eurasia, SAMOI-A is well correlated with the strength of
subtropical jet from central to East Asia while WYI and MTI are well correlated with it from Europe to
central Asia. Over the north Pacific region, MTI shows that there is a high correlation between
monsoon activities and the zonal northward shift of the north Pacific high while SAMOI-A shows that
active convection forces a propagation of quasi-stationary Rossby wave packets.
As the result of the comprehensive examinations of these indices, MTI seems to be the best
indicator for the activity of whole Asian summer monsoon. However, SAMOI-A is the most useful
index especially for Japan due to the high correlation with the development of the barotropic
anti-cyclone around Japan.
127
PHASE RELATIONS AMONG WESTERN NORTH PACIFIC
MONSOON, INDIAN MONSOON AND AUSTRALIAN MONSOON
Dejun GU1, Tim Li2, Zhongping JI3, and Bin ZHENG1
1
Guangzhou Institute of Tropical and Marine Meteorology, and Key Open Laboratory for Tropical Monsoon,
China Meteorological Administration, Guangzhou, China
2
IPRC, and Department of Meteorology, University of Hawaii at Manoa, USA
3
Guangzhou Central Meteorological Observatory, Guangzhou, China
ABSTRACT
The phase relationships of the SCS/WNP summer monsoon (WNPM) with the Australian
monsoon (AM) and Indian monsoon (IM) are investigated using observational rainfall, SST and
NCEP reanalysis data for the period of 1979-2005. It is found that WNPM has significant lead-lag
phase relationships with AM. A strong WNPM often follows a strong AM but leads a weak AM a half
year later. A significant simultaneous negative correlation appears between WNPM and IM. The
negative correlation coefficient reaches -0.64, exceeding the 99% significant level.
By examining the circulation and SST patterns associated with the in-phase and
out-of-phase relationships, several mechanisms are proposed. The in-phase relationship from AM
to the succeeding WNPM occurs primarily during the ENSO decaying phase. A warm SSTA in the
eastern Pacific induces a reversed anomalous Walker cell and causes a weak AM during El Nino
mature winter. Meanwhile, an anomalous anticyclone is induced in WNP through the Pacific-East
Asia teleconnection and is further maintained through a positive thermodynamic air-sea feedback,
leading to a weakened WNPM.
The out-of-phase relation from WNPM to the succeeding AM involves two different
scenarios: the El Nino early onset and El Nino decaying/La Nina developing. For the first scenario,
a warm SSTA in the eastern Pacific forces a Rossby wave response and low-level cyclonic shear
over WNP, which further enhances WNPM through Ekman-pumping induced boundary layer
convergence. As the SSTA develops toward boreal winter, it weakens the AM through the
anomalous Walker circulation. For the second scenario, the persistence of an anomalous
anticyclone during the El Nino decaying phase leads a weak WNPM. With the onset of La Nina in
the late year, the cold SSTA leads to a strong AM in boreal winter.
The simultaneous negative correlation between WNPM and IM appears during either the El
Nino earlier onset or the El Nino decaying/La Nina developing cases. In the former case, the SSTA
in the eastern Pacific on one hand leads to the cyclonic wind shear and thus a strong WNPM and
one the other hand anomalous subsidence over the Maritime Continent, which further suppress the
convection over India through an atmospheric Rossby wave response. In the latter case, a weak
WNPM results from the persistence of an anomalous low-level anticyclone from boreal winter to the
subsequent summer, whereas a strong IM is caused by a simultaneous cold eastern Pacific SSTA
in JJA, a basin-wide warming in the tropical Indian Ocean prior to the monsoon onset, or enhanced
convection in the Maritime Continent associated with the local Hadley circulation.
128
SENSITIVITY OF ITCZ STRUCTURE TO CUMULUS
CONVECTION PARAMETERIZATIONS ON AN AQUA PLANET
Liang GUO1,2, Yimin LIU1, Guoxiong WU1
1
State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics,
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
2
Graduate University of Chinese Academy of Sciences, Beijing 100049, China
ABSTRACT
The authors examine the performances of different cumulus convection parameterization
schemes in an aqua planet, which is zonally symmetric. The aqua planet has latitudinal-varying
SST and solar angle. The intertropical convergence zone (ITCZ) is indicated by high precipitation
the in experiments. The authors find that a single ITCZ exists with Zhang‟s scheme (Zhang and
McFarlane, 1995) or Manabe‟s scheme (Manabe et al. 1965), while double ITCZs exist with
Tiedtke‟s scheme (Tiedtke, 1989). The key for the double ITCZ is believed to be the latitudinal
variation of the evaporation in the boundary layer; and such variation is mainly caused by the
latitudinal variation of zonal wind speed, which influences the distribution of the evaporation through
the evaporation-wind feedback mechanism. The reason for a single ITCZ in Zhang‟s scheme is due
to the criterion for convection to occur more easily at the equator. As a result, precipitation
maximum can be maintained at the equator through the CISK mechanism.
Keywords: Double ITCZs, Parameterization of cumulus convection, Aqua-planet Experiment, Evaporation-wind
feedback, CISK
129
CHARACTERIZATION OF SPATIAL AND TEMPORAL
DISTRIBUTION OF MONSOON RAINFALL IN AN URBAN AREA:
MUMBAI, INDIA
Kapil GUPTA, B. LOKANADHAM
Department of Civil Engineering, Indian Institute of Technology, Bombay, India
Email: [email protected]
ABSTRACT
Rainfall has been observed to exhibit large spatial and temporal variation within urban areas.
Hence, knowledge of the precipitation distribution in time and space will enable a better hydrologic
analysis in terms of preparing better urban rainfall-runoff models. This should enable improvement
in the design and operation of urban drainage systems. This in turn, should improve modeling and
forecasting abilities to estimate urban floods and improve flood response and mitigation. This study
is aimed at deriving a better understanding of the spatial and temporal distribution of rainfall pattern
under heavy monsoon conditions and to help in evaluating the various mitigation and design
alternatives for integrated urban drainage management.
The objectives of this paper are to study the spatial and temporal variation of high intensity
monsoon rainfall from 26 automatic tipping-bucket rain gauge locations in the 471 sq km area under
the jurisdiction of the Municipal Corporation of Greater Mumbai. The technique developed in this
study can then be applied for planning drainage infrastructure in other cities susceptible to flooding
due to high intensity rainfall. A comparison of the results using various available techniques is also
presented.
Keywords: Monsoon rainfall, Mumbai, spatial correlation, temporal distribution
130
THE CLIMATOLOGICAL CHARACTERISTICS OF RAINY
SEASON IN HUANG-HUAI REGION
Yamin HU1 and Yihui DING2
1
Guangdong Climate Center, Guangzhou, China
National Climate Center, China Meteorological Administrations, Beijing, China
2
ABSTRACT
By means of Cressman‟s objective analysis method, a 0.5°×0.5° grid point daily precipitation
dataset of China for 1954~2005 has been obtained. Then, a rainy season criterion has been
defined for investigating the precipitation features in the Huang-Huai region (32~37°N, 110~123°E),
which between the Huanghe River and the Huaihe Basin Region. The defined criterion is applied to
analyze the precipitation characteristics during the rainy duration in the Huang-Huai region. On the
average, the rainy onset date is on July 8, the ending date on July 26, the rainy duration persists
for16 day and the precipitation intensity is 2.48. The results show that there is a prominent
inter-annual and inter-decadal variation of rainfall in Huang-Huai region since 1954a. According to
the power spectrum, the maximum entropy spectrum and the Morlet wavelet analysis method, the
52a precipitation period features are analyzed. The rainy parameters have an about 2~3a and
16~18a dominating periods, while the 2~3a significant period almost concentrate after the mid of
1990‟s. The approximate 2~3a significant period of rainy parameters (including the onset date, the
end date, the rainy duration, the rainy precipitation and the intensity index) may reflect the effects of
Tropospheric Quasi-Biennial Oscillation (TBO). The climatic jumps of parameters over the
Huang-Huai region are detected in terms of the moving T test technique, Yamamoto signal noise
ratio method and Mann-Kendall (M-K) test method. The obvious abrupt climatic changes have
happened in the early of 1960‟s. Furthermore, the atmospheric circulation characters, including the
water vapor transport of the summer monsoon as well as the permanent and maintenances of the
West-North Pacific subtropical high and the mid-high latitude blocking high, are discussed for rich
and poor rainy years, respectively.
Key words: Rainy season in Huang-Huai region, defined criteria, climatological characters
131
EXISTENCE AND INTERANNUAL VARIATIONS OF A
LOW-FREQUENCY (55-100DAY) MJO MODE IN AUSTRAL
SUMMER - ROLE OF OCEANIC DIURNAL WARM LAYERS
Takeshi IZUMO, Sebastien MASSION, Jérôme VIALARD, Madec, de
Boyer MONTÉGUT, LUO, BEHERA, TAKAHASHI and YAMAGATA
LOCEAN – IPSL, Univ. Pierre et Marie Curie, Paris, France
ABSTRACT
The Madden-Julian Oscillation is the main component of the intraseasonal variability of the
convection in the tropics. Previous work had already suggested that the timescale of the MJO
increased in Austral summer while going from the equator to ~8°S. Here we suggest, based on
observational records, that there are two intraseasonal modes of variability of the convection in
Austral Summer. One is higher frequency (30-50 day) and more symmetric with respect to the
equator, while the other is asymmetric (shifted to the south) and more low-frequency. Both modes
have independent interannual variations, and the variations of the lower-frequency mode appear to
be modulated at ENSO and IOD timescales. Similar analyzes performed on a coupled general
circulation model that resolves diurnal cycle also extract the two modes, and allow more insight in
their mechanisms. It appears that coupling with the surface ocean, with oceanic diurnal warm layers
and related diurnal cycle of SST in particular, is important to reproduce the 55-100 day mode.
132
PREDICTABILITY OF ENSO AND MONSOON
Emilia K. Jin, James L. Kinter III, V. Krishnamurthy
and Jagadish Shukla
George Mason Univ., Center for Ocean-Land-Atmosphere Studies, Fairfax, Virginia, USA
ABSTRACT
The characteristics of ENSO predictability and associated monsoon predictability are
investigated from 12 CGCM hindcasts. The CGCM datasets that come from the APCC/CliPAS
(APEC Climate Center/Climate Prediction and its Application to Society) and DEMETER (European
Multimodel Ensemble system for seasonal to interannual prediction) projects are used. The 12
models used are fully coupled ocean-land-atmosphere dynamical seasonal prediction systems with
5- to 9-month integrations for 3 to 15 different initial conditions for four seasons in the common 23
years from 1981 to 2003. As a reference, dynamic-statistical SST forecast skill for tier-two forecast
system is also compared.
Though the state-of-the-art CGCM is regarded as one of the most promising class of tools
for producing seasonal forecasts, it still has significant errors in simulating the mean climatology
and variability of the tropical oceans. It is also well known that prediction of sea surface temperature
(SST) anomalies on seasonal time scales in the central and eastern Pacific is very crucial to the
associated global-scale climate anomalies of precipitation and near-surface air temperature. As the
most dominant source of error in ENSO prediction, several aspects of model flaws including slow
coupled dynamics and monotonic flavor of El Niño are explored by comparing forecast and free
long run dataset from same model, since the systematic errors in the long run are reflected in the
forecast skill as a major factor limiting predictability after the impact of initial uncertainties fades out.
Monsoon predictability associated with ENSO is also investigated. The ability of the CGCMs to
simulate two dominant oscillatory modes at 45-day and 28-day time scales and the seasonally
persistent modes related to ENSO and Indian Ocean, as found in observations, is assessed. In
particular, the role of forced modes of the daily monsoon in determining the seasonal mean
monsoon rainfall and its interannual predictability are examined.
A simpler coupled system can be considered which includes the simultaneous operation of
local coupling and remote forcing to diagnose the problems of CGCMs to simulate the
ENSO-related rainfall in the Americas. To mimic the important aspects of this air-sea coupling while
maintaining the flexibility to attempt to simulate the observed climate, the "pacemaker" experiments
where tropical Pacific SST is prescribed from observations but coupled air-sea feedbacks are
maintained in the other ocean basins were designed. For this experiment, the NCEP Global
Forecast System (GFS) which is the atmospheric component of the Climate Forecast System (CFS)
is coupled with simple slab ocean mixed-layer model. A 56-year simulation from 1949 to 2004 with
4 different initial conditions is performed. An additional TOGA type experiment is made by using
climatological SST instead of coupling with the slab ocean model. This run is used as a “control” for
the pacemaker experiment in order to evaluate the effect of local air-sea interaction.
The relationship between ENSO and Asian monsoon in these experiments is not only a
good example of air-sea coupled co-variability, but also an interesting subject for this model
because CFS CGCM long run cannot mimic this relationship very well. CGCM shows weak
relationship with Indian monsoon with insignificant confidence level and delayed signal with western
North Pacific monsoon different from observation. Surprisingly, simulated relationship in pacemaker
is reasonably close to observed. Analysis of dominant mode of monsoon field associated with
ENSO also shows good accordance with observed. This improvement in pacemaker comparing to
CGCM shows that simple systems with the only local air-sea feedback are capable of greater
realism than sophisticated coupled models, since the CGCM has significant errors in the ocean
dynamics and Walker circulation related with ENSO. The control run without (continue to Page 134)
133
INDIAN OCEAN DIPOLE MODE: POSSIBLE PREDICTOR FOR
THE EAST ASIAN SUMMER MONSOON
R. H. KRIPALANI
Indian Institute of Tropical Meteorology, Pashan, Pune 411008, India
Email: [email protected], [email protected]
ABSTRACT
The relationship between the Indian Ocean Dipole Mode and the East Asian Summer
Monsoon is examined. Results reveal that the peak positive phase of the dipole during autumn
suppresses the following summer monsoon activity over East Asia three seasons later, in particular
over the South China-Korea-Japan sector and the adjacent west Pacific region. Composite and
correlation analysis suggests that the autumn positive phase induces heavy snow over eastern
Eurasia north of the Korea-Japan peninsula during the following winter and spring seasons. This
suppresses the warming rate keeping the troposphere cooler and transporting cold and dry air from
the north during summer over the Korea-Japan and the adjacent regions. Furthermore, the sea
surface temperature reveal that the positive phase of the dipole mode during autumn is associated
with the warm phase (El Nino) of the El Nino Southern Oscillation over the Pacific. As the seasons
progress through to summer, the warm phase over the Pacific transforms to a developing cold
phase (La Nina). Both the anomalous northerly winds due to heavy snow and the anomalous warm
sea surface temperature over the west Pacific due to the La Nina displace the North Pacific
Subtropical eastwards, resulting in a weak cross-equatorial flow and a weak low-level jet. This
inhibits moisture supply from the Pacific leading to subdued rainfall activity. The memory for
delayed impact three seasons later is carried by the snow distribution over Eurasia by the northern
route and the sea surface temperatures over East Indian Ocean-west Pacific region via the
Indonesian Through-Flow sector by the southern route.
During the autumn (SON) of 2007 positive dipole mode prevailed over the Indian Ocean. It
was speculated that the positive mode may have an adverse impact on the summer monsoon
rainfall (June-July-August 2008) over South China-Korea-Japan sector and may lead to below
normal rainfall activity (Kripalani 2007). The heavy unprecedented snow witnessed in northern
China during last week of January / first week of February 2008 could be due to the positive dipole
during autumn of 2007. Furthermore the APEC Climate Center (Busan, South Korea) have also
issued forecast for below normal rainfall over South China-Korea-Japan during JJA 2008.
References:
R.H. Kripalani 2007: A possible mechanism for the delayed impact of the Indian
Ocean Dipole Mode on the East Asian Summer Monsoon. APCC [APEC {Asia-Pacific
Economic Co-operation} Climate Center, Busan, South Korea] Newsletter, Vol. 2 No 4,
December 2007, pp 4-6 (http://www.apcc21.net)
coupled ocean also simulates it less well. In pacemaker, decadal change of
ENSO-Indian monsoon relationship is not shown for 55-year period, while clearly shown for
western North Pacific. It suggests decadal change of eastern Pacific ENSO anomalies strongly
linked with that of western North Pacific monsoon. Based on this result, the cause of decadal
134
change of monsoon is investigated.
(from Page 133)
INTERDECADAL VARIATIONS OF MERIDIONAL WINDS IN THE
SOUTH CHINA SEA AND THEIR RELATIONSHIP WITH SUMMER
CLIMATE IN CHINA
LI Chunhui1, Tim LI2, LIANG Jianyin1, LIN Ailan1, GU Dejun1, ZHEN Bin1
1
Institute of Tropical and Marine Meteorology/The key open laboratory for tropical monsoon, CMA,
Guangzhou, China.
2
Department of Meteorology, University of Hawaii, Honolulu, Hawaii, USA
ABSTRACT
Both the NCEP reanalysis and the Xisha Island station data analyses indicate that the
low-level meridional wind (LLMW) over the SCS experienced an interdecadal variation since the
late 1970s. The LLMW change is associated with the reduction of tropospheric temperature in the
mid-latitude East Asia. A mechanism is put forward to explain the triggering and maintenance of the
tropospheric cooling. The convective heating over the southern South China Sea results in a
meridional vertical overturning circulation, with anomalous descending motion appearing over
continental East Asia. The anomalous descending motion reduces the local water vapor through
both anomalous low-level divergence and vertical dry advection. The decrease of tropospheric
humidity leads to the enhanced outgoing longwave radiation into space, and thus cold temperature
anomalies. The decrease of the temperature and thickness leads to the low (high) pressure
anomaly and convergent (divergent) flows at upper (lower) levels. This further enhances the
descending motion and leads to a positive feedback loop.
The fall in tropospheric temperature over the East Asia reduces the land-sea thermal
contrast and leads to the weakening of cross-equatorial flows and thus the LLMW over SCS. A
further diagnosis indicates that the LLMW is closely linked to the climate variation in China on the
interdecadal timescale. It is associated with a “－,＋,－,＋” meridional rainfall pattern, with less rain
in Guangdong Province and North China but more rain in the Yangtze and Huaihe River basins and
Northeast China, and a “＋、－、＋” pattern for the surface temperature, with positive (negative)
temperature anomalies in the South and North (Central) China.
Key words: Meridional wind in South China Sea, interdecadal variation, land-sea thermal contrast, meridional overturning
circulation, precipitation and temperature in China
135
WHAT CAUSED MONSOON ONSET OVER SOUTH AMERICA?
Wenhong LI and Rong FU
Earth and Atmospheric Sciences, George Institute of Technology
311 Ferst Drive NW, Atlanta GA, USA
ABSTRACT
South American monsoon shares some features of classic Asian monsoon but also has
unique characteristics. Using ECMWF reanalysis data, we have studied the processes critical for
the monsoon onset over South America. The initiation of the monsoon starts from the increase of
the local latent heat flux and therefore the local build-up of the available potential energy. The
cross-equatorial flow and upper tropospheric circulation remain unchanged from those of the dry
season. The developing phase is dominated by the seasonal transition of the large-scale circulation,
which accelerates by dynamic feedbacks to an increase of locally thermal-driven rainfall. During this
stage, the reversal of the low-level, cross-equatorial flow in the western Amazon increases moisture
transport from the tropical Atlantic Ocean and leads to net moisture convergence to the monsoon
region. In the upper troposphere, the divergent kinetic energy begins to be converted into rotational
kinetic energy, and geopotential height increases rapidly. These processes lead to the onset of the
South American monsoon and increase of anticyclonic vorticity at the upper troposphere. After
onset, the lower tropospheric potential energy reaches equilibrium, but the conversion from
divergent to rotational kinetic energy continues to spin up the upper troposphere anticyclonic
circulation associated with the Bolivian High to its full strength. Our interannual analysis also
suggested the mechanism.
136
THE INTERANNUAL CHARACTER OF EAST ASIAN
SUBTROPICAL MONSOON FROM MAY TO AUGUST
LIAN Yi, SHEN Baizhu, LIU Gang, LI Shangfeng, GAO Zongting
Lab. of Res. for Middle-High Latitude Circulation System and East Asian Monsoon, Changchun, Jilin, China
Institute of Meteorological Science of Jilin Province, Changchun, Jilin, China
1.
ABSTRACT
According the standard of East Asian Monsoon onset that we defined before we divided the
traces of East Asian subtropical Monsoon were into three main kinds in this study, including the
westward (along the west of 110°E ),the middle (during 110°E-115°E) and the eastward (along the
east of 110°E) kind . In addition, the traces‟ time of East Asian subtropical Monsoon we studied
here is from May to August.
It is also found that there are obviously QBWO( Quasi-Biweekly Oscillation ) character on
the anomaly field of 850hPa wind, 500hPa geopotential height, 500hPa vorticity and the main land
precipitation from Jun to August.
2.
DATA AND METHOD
For this study, we use the daily mean data from the National Centers for Environmental
Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis. Time of this kind
data covers from 1948 to 2002. Data set has a 2.5*2.5 horizontal resolution and extends from 1000
to 10 hPa with 17 pressure levels in the vertical. We also employ the daily mean data comes from
ECWMF, covering from 1958 to 2002. In addition, we use the daily precipitation data from 618
China stations, covering from 1961 to 2005.
Fig. 1. The distribution of East Asian Monsoon onset measured by the standard that we defined
before.(from left to right are three main kinds monsoon onset trace: the westward, the middle and the
eastward. In addition, each kind monsoon account for 22%,64%,14% during 1948-2002,from left to right )
Fig. 2. The distribution of precipitation in the main land.(from left to right divided according to Fig.1 )
Fig. 3. The monthly anomaly of geopotential height of 500hPa in Jun. (from left to right divided
according to Fig.1 )
Fig. 4. The monthly anomaly of wind field of 850hPa in Jun. (from left to right divided according to
Fig.1 )
Fig. 5. Quasi-Biweekly Oscillation character on the field of 500hPa vorticity in three typical monsoon
years respecting the westward ,the middle and the eastward monsoon onset.(years from left to right are
1997,1998,1994)
3.
CONCLUSION AND DISCUSSION
When the monsoon onset on the westward trace we can find that the precipitation in the
main land caused by monsoon is in provinces of Guan Xi,Zhe Jiang,Fu Jian,Yun Nan,Gui Zhou and
north of Hei Longjiang.
While the monsoon onset on the middle trace, the main rain band is in North China area and
Middle and lower reaches Yangtze River.
And when the monsoon onset on the eastward trace, the main rain band is in provinces of
Guang Dong, Guang Xi,Fu Jian and east of Zhe Jiang.
Analysing Quasi-Biweekly Oscillation character of 500hPa vorticity field we found that :
when the monsoon onset according to the westward, Quasi-Biweekly Oscillation on the field of
500hPa vorticity transmit northward actively in the area of North of 10°N and South of 30°N.While
the monsoon onset according to the mid-ward,Quasi-Biweekly Oscillation transmit northward
actively in the area of 102.5°E-110°E. And when the monsoon onset according to the eastward
Quasi-Biweekly Oscillation transmit southward instead.
The study we did here is a sample and we will continue further research in the future.
137
ENERGY SPECTRUM CHARACTERISTICS OF BOREAL
SUMMER INTRASEASONAL OSCILLATIONS: CLIMATOLOGY
AND VARIATIONS DURING THE ENSO DEVELOPING AND
DECAYING PHASES
Ailan LIN1, Tim LI2
1
Institute of Tropical and Marine Meteorology/Key Open Laboratory for Tropical Monsoon, China
Meteorological Administration, Guangzhou, China
Email: [email protected]
2
IPRC and Department of Meteorology, University of Hawaii, Honolulu, Hawaii
ABSTRACT
The geographic-dependence characteristics of energy spectrum of the boreal summer
intraseasonal oscillation (BSISO, May-October) over the Indo-western Pacific region were analyzed
using the 25-yr (1979-2003) observational data. The BSISO energy spectrum distribution exhibits a
distinctive regional characteristic. The stationary and eastward propagating modes are most
pronounced at the equator (5°S-5°N), while the westward propagating modes are dominant in the
off-equatorial region (10°N-20°N). While the eastward ISO spectrum agglomerates on the
30-60-day period and zonal wavenumber-1, the westward mode covers wider spatial (wavenumber)
and temporal (period) range. Along the Arabian Sea, Bay of Bengal and SCS latitudes, the
dominant wavenumber-1 mode is the eastward (westward) propagation at the 30-60-day
(10-20-day) period; for zonal wavenumber-2, the dominant mode is the westward propagation at
both the 30-60-day and 10-20-day periods. Compared to the absolute amplitude of both zonal and
meridional mode energy spectrum, northward propagation is the most predominant mode in boreal
summer over the Indo-western Pacific regions. The strongest northward propagating BSISO signal
appears in the eastern tropical Indian Ocean.
The variation of BSISO differs significantly in the El Nino and La Nina developing and
decaying phases. During the El Nino (La Nina) developing summer, the eastward propagation is
enhanced (weakened) at the equator, while the northward propagation is also strengthened
(weakened) over the western Pacific (east of 140°E). During the El Nino (La Nina) decaying
summer, the eastward propagation weakens (strengthens) at the equator, opposite to that in the
developing summer; the westward propagation off the equator and the northward propagation over
SCS and western Pacific are suppressed (enhanced). The amplitude of the BSISO variation is
stronger in the decaying summer than that in the developing summer. This asymmetry in BSISO
variations is primarily attributed to the asymmetry of the background mean flow change associated
with the developing and decaying phases of ENSO.
138
THE IMPACT OF PRE-MONSOON OVER THAILAND
Maytee MAHAYOSANANTA
Thai Meteorological Department, 4353 Sukhumvit Rd., Phrakanong
Bang Na, Bangkok 10260 Thailand
E-mail: [email protected]
ABSTRACT
Located on the region of Southeast Asia, Thailand is one of the countries normally
dominated by the southwest and northeast monsoon. At the end of April in a year, moving through
southern Thailand, easterly waves from the South China Sea would always bring thundershowers
and strengthen an active low cell to become a possible tropical cyclone over the Bay of Bengal. The
cyclone, for example “NAGIS” on May 2008, would then make landfall above the lands and also
cause abundant rainfall, flooding and landslide around the area.
In the study on The Impact of Pre-monsoon over Thailand, the selected time was in the
pre-rainy season from 25 April to 5 May 2008. The instruments of Unified Model V4.3 and MTSAT
were applied for the following data: synoptic system, 850, 500 and 200 hPa upper wind system and
MTSAT cloud aerial imageries. Comparing with the rainfall volume of meteorological stations, the
values of model weather forecast, as the result of this study, were though a few overlapped due to
the difference of data resolution and the improper time; the model could be used as a guidance for
an early warning system in the pre-monsoon season for reducing human life and property.
139
ASSESSING WET SEASON RAINFALL CHARACTERISTICS
FOR NORTHERN AUSTRALIA AND NORTHEASTERN BRAZIL
USING COX (NON) PROPORTIONAL HAZARD MODELS
Holger MEINKE*1 and Aline H.N. MAIA 2
1
Crop and Weed Ecology, Department of Plant Sciences, Wageningen University,
Wageningen, The Netherlands
2
Embrapa Meio Ambiente,, Jaguariúna, SP, Brazil
ABSTRACT
In many tropical regions the onset of monsoonal rains as well as the amount of rain received
during the wet season is highly variable. This seasonal variability can cause problems for climate
sensitive sectors such as agriculture. Some of this variability is related to ENSO and is therefore at
least partially predictable. Seasonal predictions can be obtained either via statistical methods (e.g.
statistical relationships between ENSO indicators such as SST anomalies or SOI and historical
rainfall dates or amounts) or from GCM output. Such predictions can influence risk management
practices, providing the information is communicated to decision makers in a fashion that is
compatible with the decision making process. Further, the degree of predictability and the
uncertainties associated with the predictions need to be communicated well to assist with sound
risk management practices. Here we present case studies for two locations (Darwin, Northern
Australia and Quixeramobim, Northeastern Brazil) that show how Cox Regression Models (CRMs)
can be used to provide such information. For Darwin, we fitted non-proportional CRMs to onset date
and found strong, non-linear relationships between SOI values in JJA preceding the wet season
and probability of a late onset (defined as 15% of total average wet season rainfall received after 1
September). Median onset dates ranged from 18 November to 20 December when the preceding
JJA SOI was either -15 or +15, respectively. For Quixeramobim we show a strong relationship
between Nino3.4 SST anomalies in the preceding ONDJF period and total wet season rainfall
(MAMJ), with median wet season rainfall values ranging from 392mm to 567mm for SST anomalies
of either +1.5 or -1.5, respectively.
Our study shows how to objectively assess the influence of each candidate predictor on the
predictant and how to estimate probability of exceedance curves with respective confidence bands.
We also propose a novel probabilistic forecast approach in which statistical models such as CRMs
are used in conjunction with GCM output to account for the uncertainty arising from the „prediction
of the predictors‟. We show that CRMs are a valuable modelling technique that can combine climate
information arising from historical series and from GCM forecasts.
* Corresponding Author: E-mail: [email protected]; Phone: +31 3174 84772
140
CYCLONE TRACK CLIMATOLOGY IN NORTH INDIAN OCEAN
AND TRACK FORECAST OF NARGIS
IN THE JMA ENSEMBLE FORECAST DATA
Tetsuo NAKAZAWA
Typhoon Research Department, Meteorological Research Institute, Japan
ABSTRACT
Cyclone Nargis brought severe damage on Myanmar. Climatological steering flows are
computed to understand the common tracks in the North Indian Ocean. An ensemble forecast
dataset of the JMA is also used to analyze the track probability of Nargis. The result shows that
some members could predict the landfall in Myanmar more than a week in advance. However, the
forecast data more than a week in advance give landfall in south India.
141
PRECIPITATION BURSTS IN THE NORTH AMERICAN
MONSOON
Stephen W. NESBITT and Nicole J. SCHIFFER
Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, USA
ABSTRACT
In this study, we will demonstrate the utility of using high resolution precipitation products
(such as TRMM 3B42, and CMORPH), as well as operational Long Range Detection Network
(LRDN) cloud-to-ground flash data, and Tropical Rainfall Measuring Mission Lightning Imaging
Sensor (LIS) and Precipitation Radar (PR) measurements to quantify the characteristics of
convection and “precipitation bursts” over the Sierra Madre Occidental in Mexico and Southwest
USA during the North American Monsoon. In particular, characteristic changes in the structure of
precipitation systems due to environmental forcing, proximity to terrain, and precipitation vertical
structure are found that are important modulators of rainfall in the region.
In addition, intraseasonal variations in monsoon precipitation can be examined at
unprecedented temporal and spatial scales using the above datasets. We will show how convective
characteristics change with synoptic and mesoscale meteorological forcing mechanisms known to
modulate monsoon rainfall, including gulf surges, tropical easterly waves TEWs, and the intensity of
the Gulf of California Low Level Jet LLJ. Our analyses also show that the rainfall to cloud to ground
lightning flash ratio (or rain yield) differs substantially pre- and post-monsoon onset, and then
remains relatively constant once this shift occurs. This fact makes quantitative monsoon
precipitation monitoring with lightning data feasible. We also find that monsoon convection in the
North American Monsoon is more intense during its active phase, which is the opposite response
when compared to the Asian, Australian, and South American Monsoon systems. This difference in
latent heating characteristics likely has key implications on the large scale structure of the North
American Monsoon.
142
PROGRESS OF MONSOONS IN THE PHILIPPINES
DURING THE 2007-2008 LA NIÑA EVENT
Daisy F. ORTEGA
Philippine Artmospheric, Geophysical and Astronomical Services Administration (PAGASA),
Department of Science and Technology, Manila, Philippines
ABSTRACT
The common climate feature that influenced the intraseasonal rainfall variability in the
Phlippines is the Southwest and Northeast monsoons. These bring wet season to the western and
eastern part of the country respectively. Tropical cyclones which can cause catastrophic flooding if
they reach land are more likely to occur in the monsoon season. It usually triggers the onset of the
rainy season associated with the southwest monsoon under type1 Climate (Western section of
Luzon and Visayas). Intensity of monsoon is linked to ENSO phenomenon, the El Niño and the La
Niña. Philippines has been called the home to the El Niños and the La Niñas, owing to its
geographical location, within the equatorial Pacific ocean. This renders the country vulnerable to
the effects of the El Niño Southern Oscillation (ENSO) events. However, there could be devastating
consequences if the monsoon failed to arrive. The intent of this study therefore is to investigate the
progress especially, of the southwest monsoon where onset of the rain in the country is associated
with, during the 2007-2008 La Niña episode. These include progress in synoptic scale showing
weather systems that affected the country during the period. Impacts of the monsoon to the
country‟s water resource, agriculture, environment and society are likewise tackled.
143
COUPLED-MODEL SIMULATIONS OF THE TROPICAL
NORTHWEST PACIFIC PRECIPITATION RELATED TO ENSO
AND ASIAN MONSOON PREDICTION
Tomoaki OSE1*, Tamaki YASUDA1and Yuhei TAKAYA2
1
Meteorological Research Institute (MRI), Tsukuba, Japan
2
Japan Meteorological Agency (JMA), Tokyo, Japan
ABSTRACT
The East Asian climate is influenced by convective activity over the tropical Northwest (NW)
Pacific through atmospheric teleconnections in both boreal winter and summer seasons.
Fortunately for the seasonal prediction in East Asia, the variability of precipitation in the NW Pacific
is related to highly predictable NINO3 SST to some extent. The relationship is clear in the boreal
wintertime. It is interesting that the NW Pacific precipitation in boreal summertime has significant
correlations with the previous wintertime NINO3 SST.
We examined how well the relationship between the NW Pacific precipitation and NINO3
SST is reproduced by coupled models including the JMA/MRI seasonal prediction model and the
CMIP3 models.
The JMA/MRI seasonal forecast model successfully predicts the inter-annual variability of
the NW Pacific precipitation not only for the boreal wintertime but also for the boreal summertime
with more than six-month lead time. This fact leads to good seasonal hindcast skills for the summer
Asian Monsoon. Consistently, the model reproduces the observed relationship between the NW
Pacific precipitation and NINO3 SST well for both seasons in seasonal prediction experiments
starting from real initial conditions. But, these relationships are influenced by the nature of the
model‟s long-term run.
It is an interest to see how well the CMIP3 models naturally simulate the relationship
between the NW Pacific precipitation and NINO3 SST in their long runs. Many models reproduce
the relationship for the wintertime relatively well. On contrary, only very few models are able to
reproduce the summertime relationship between the NW Pacific precipitation and NINO3 SST. The
characteristics of the successful models would be reported.
*Presenter and corresponding author: [email protected]
144
ON THE SIMULTANEOUS RELATIONSHIPS BETWEEN NORTH
ATLANTIC SEA SURFACE TEMPERATURE ANOMALIES AND
INDIAN SUMMER MONSOON RAINFALL
M. RAJEEVAN and Latha SRIDHAR
National Climate Centre, India Meteorological Department, Pune- 411 005 INDIA
ABSTRACT
Indian summer monsoon rainfall (ISMR) exhibits strong inter-annual variations, influenced
by Sea surface temperature variations over the equatorial Pacific, Indian Oceans and winter snow
cover over NW Europe. Recently, Goswami et al (2006) have discussed the physical mechanism
for the influence of Atlantic Multi-decadal Oscillation (AMO) on the Indian monsoon through the
changes in the tropospheric temperature changes over Eurasia. Chang et al (2001) and Srivastava
et al. (2002) also established the relationships of North Atlantic circulation anomalies and Indian
monsoon. In the present study, we address the simultaneous inter-annual relationship between
North Atlantic SST anomalies during July-August-September and Indian monsoon rainfall. For this
study, monthly SST and rainfall data for the period 1951-2005 have been considered. For
representing monsoon rainfall over India, seasonal rainfall over the monsoon core region
(geographical region consisting part of central India and NW India) was considered. Simple
correlation, canonical correlation analysis (CCA) and composite methods have been used to
examine the relationships.
There are statistically positive significant correlations between the SST anomalies averaged
over the North Atlantic Ocean (between 300- 450N) and ISMR, suggesting positive anomalies of
SSTs are conducive for good monsoon rainfall over India. These correlations show significant
epochal variations. The correlations have become stronger during the recent years, especially after
mid 1970s. Such an epochal variation is also observed with the SST anomalies over the Pacific and
Indian Oceans. While the correlations between the Pacific SST anomalies associated with ENSO
and ISMR weakened after mid-1970s, the relationship of north Atlantic SST anomalies has now
strengthened. Further analysis shows that the positive SST anomalies over the north Atlantic
Ocean are caused by the strengthening of Azores High, which drives warm oceanic waters
pole-wards with the associated anomalous anticyclonic flow. The Canonical Correlation Analysis
(CCA) of the SST over the North Atlantic Ocean and seasonal rainfall over the monsoon core region
shows that canonical correlations of the first three coupled patterns are 0.67, 0.43 and 0.37, which
account together about 34% and 30% of the variance of SST and rainfall respectively. The SST
anomalies over the north Atlantic are responsible for the intensification and shift of subtropical north
Atlantic westerly jet stream to higher latitudes and formation of stronger Tibetan anticyclone and
hence Indian monsoon circulation and rainfall. Thus, Atlantic SST anomalies and associated
circulation anomalies became an important source of variability of the Indian summer monsoon
rainfall during the recent years.
145
A NEW METHOD OF IDENTIFICATION AND TRACKING OF
STORMS FROM SATELLITE IMAGES
E.M. RANJINI and R. KARTHI
Dept. of Computer Science, Amrita Vishwa Vidyapeetham, Ettimadai.Tamil Nadu, India
Email: [email protected], [email protected]
ABSTRACT
Natural phenomenon is always unpredictable. Such phenomenon is always predicted in a
probabilistic approach. This paper proposes a method to identify and track storms using the
movements of cloud patches. The images used for this purpose is taken using IR satellites. To do
this prediction a sequence of satellite images are used, which is taken at regular intervals. When a
cloud moves above ocean it collects huge amount of water and it may turn out to be powerful
storms.
Our approach uses the following methods to track the movements of cloud segments. Firstly
the image taken from the satellite is cropped manually. The image is then segmented using K
means clustering. Value of K is chosen arbitrarily. For each cluster average gray value is calculated
and the cluster with largest gray value is taken as cloud segment. Binarize the image such that all
the clusters other than the cloud cluster are replaced with value 1 and cloud clusters with 0. For
each such cloud segments different regions are calculated using connected component analysis. A
smallest bounding box is calculated for these regions.
In the next phase, the association between corresponding regions of consecutive images is
done using a nearest neighborhood approach. For this purpose we have calculated some features
like coordinate positions, average of x coordinates, average of y coordinates and centroid for both x
and y coordinates for each region. An association matrix is generated based on the better match
between the feature matrices of image 1 and image 2. Again association matrix is calculated for
image 2 and image 3. Use the above two matrices to find all the possible paths between the three
image frames. Then among all those possible paths we have found the best path using fuzzy logic.
For all the paths strength is calculated by finding the match using Gaussian function. Arrange the
paths according to the value of strength.
During the last phase, i.e. finding Cloud Motion Vector (velocity, angle), take each paths and
use the parameters average x coordinate and average y coordinate for finding displacement and
angle of movement.
146
FORECASTING PROBLEMS OF HIGH-IMPACT WEATHER
DURING SUMMER MONSOON IN PAKISTAN
RASUL, G. and Q. Z. CHAUDHRY
Pakistan Meteorological Department, Islamabad-Pakistan
ABSTRACT
Pakistan is located at the western frontier of the Indian Summer Monsoon which normally
prevails from July to September. Sometimes onset of monsoon is triggered in second half of June
due to cyclonic activity in the Bay of Bengal and the north Arabian Sea. Heavy precipitation events
are generally linked with tropical depressions formed over the Bay of Bengal which reach Pakistan
after crossing Indian Peninsula (Chaudhry, 1989). Sometimes, strong convection under the
influence of western disturbance and easterly moisture incursion gives rise to local storms. It
happens so rapidly that not only it brings a big surprise for experienced forecasters but also
numerical models fail to capture the magnitude and intensity. Diagnostic analysis and numerical
simulation on two such cases (Rasul et. al., 2004 & 2005) of heavy rainfall in northern and southern
parts of Pakistan were carried out and missing links in forecasting techniques were identified. The
mechanism of heavy precipitation events along foothills of Himalayas in the north (where orographic
lifting plays vital role) differ from the southern arid low elevation plains (strong convection - key
parameter to develop stormy weather).
Tropical Cyclones of the north Arabian Sea are another source of torrential rains over the
southern parts of Pakistan adjoining the coast. Bay of Bengal is the birth place of Tropical Cyclones,
moving west- or northwestward and losing intensity over the land cross India and enters in the form
of weak low in the Arabian Sea off Mumbai coast. Triggered by moist convection, they reactivate
sometimes developing into tropical storm and recurve clockwise into the Indian Gujrat affecting
southeastern parts of Pakistan. During the year 2007, two tropical cyclones developed in the North
Arabian Sea i.e. Gonu (first week of June) and Yemyin (last week of June). Former set a new record
to be the first super cyclone of the Arabian Sea which moving westward had its first landfall on the
Oman coast then crossing the Persian Gulf landed in Iran. Interestingly, the Tropical Cyclone
“Yemyin” made a rare landfall on Pakistan coast and resulted into record breaking heavy downpour
over two provinces of Pakistan. The intensity of the cyclonic storm and extent of damage are the
stunning challenge for the local forecasters and numerical modelers. This unusual track was a big
surprise to the storm track forecasters. The anomalous behaviour has been widely studied by the
local meteorologists yet there are several questions to be answered (Rasul, et. al., 2008).
147
WEST AFRICAN WEATHER SYSTEMS IN THE DEVELOPMENT
OF TROPICAL CYCLONES
SALAMI T.1, O.S IDOWU2, E.E BALOGUN3
1
Forecast Office, Nigerian Meteorological Agency, Murtala Mohammed International Airport Ikeja Lagos,
P.M.B 1215, Oshodi Lagos, Nigeria
Email:[email protected]
2
Central Forecast Office, Nigerian Meteorological Agency, P.M.B 1215, Oshodi Lagos, Nigeria
Email:[email protected]
3
Department of Physic, Obafemi Awolowo University Ile Ife Osun State, Nigeria
ABSTRACT
Tropical Cyclones have their origins from areas of low atmospheric pressure over warm
waters in the tropics or subtropics. We have have carefully studied the interconnection between the
West African Weather Systems (WAWS) and their subsequent development into Tropical Cyclones.
Between 2004 and 2005, we studied the interconnection and the teleconnection between
the WAWS and the various occurrences of Tropical Cyclones and their eventual development into
Hurricanes. We noted that critical synoptic characteristics and the environmental properties of the
Systems;the thermodynamic conditions of the storms trajectory and the conditions of the ocean are
all closely linked. It is therefore believed that proper understanding and monitoring of these systems
will play a very vital role in early detection of potential WAWS that may develop into Tropical
Cyclones and even Hurricanes. More practical issues will be presented.
It was recorded that over the period 1992-2001, weather and climate-related disasters
especially those of Tropical Cyclones origin killed about 622000 people, affected more than two
billion, left millions more homeless, devastated arable land and spread diseases.
148
FLOODS OF MONSOON NEPAL 2007- A METEOROLOGICAL
STUDY
Rajendra P. SHRESTHA
Senior Divisional Meteorologist, Meteorological Forecasting Division,
Tribhuvan International Airport, Kathmandu Neapl
ABSTRACT
The variability of Southwest Monsoon rainfall over Nepal is very high. Due to this reason
water induced disasters like landslides, floods, debris flow and Glacier Lake Outburst Floods are
frequent occurs that cause heavy loss of human lives and physical properties worth billions of
rupees each year.
During last year 2007, monsoon floods and landslides affected altogether forty-seven
districts out of seventy-five districts especially southern plain districts. The statistics carried out by
Nepal Red Cross Society (NRCS) by the end of August 2007 showed that 467,742 people of 78.606
families have been affected. Similarly 70,605 houses have been damage completely or partly and
22,257 families displaced. The death toll has been put at 146.
During the period 20 July -20 August 2007 there have been 15 occasions when the
monsoon rainfall was above 100 mm and four occasions above 200 mm mostly in Tarai plains.
An attempt has been made in this paper to identify the important synoptic situations that
results in widespread rainfall activity in the southern plains of Nepal during 2007‟s monsoon season
based on all observational data, latest satellite inputs and NECP/NCAR reanalysis data.
149
ANALYSES AND SIMULATIONS OF AIR-SEA COUPLING
PROCESS DURING 1998 TYPHOON FAITH
SUN Lu1, ZHENG Quan’an2, TANG Tswen-Yung3, CHUANG Wen-Ssn3,
LI li4, HU Jianyu5, WANG Dongxiao1*
1
LED, South China Sea Institute of Oceanology, Chinese Academy of Science, Guangzhou, China
2
University of Maryland, College Park, Maryland, USA
3
Pacific Science Association, c/o Code MR/CP Naval Postgraduate School, Monterey, California, USA
4
Third Institute of Oceanography, State Oceanic Administration, Xiamen, China
5
State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China
ABSTRACT
Three ATLAS buoys appending ADCP were moored in the South China Sea during the
South China Sea Monsoon EXperiment (SCSMEX) in 1998 to measure the temperature, salinity,
and velocity. Typhoon Faith passed around 600 km west to mooring station at 12°58.5‟N,
114°24.5‟E during Dec. 11-14. Data analyses indicate that the typhoon winds caused great
increase in energy at near inertial frequencies with two maximum in the mixed layer and themocline.
Near-inertial oscillations were observed in all upper 270 m. The major current response during this
period was near-inertial oscillations. These oscillations were excited right after the arrival of the
typhoon. The amplitudes of the oscillations decreased with depth and the oscillation propagated
downward. The near-inertial oscillations are also seen in temperature and salinity. Eventually we
simulate the behavior of pre-existing near inertial oscillations in a two-layer model ocean with an
approximate wind field following a soliton-like function. The theoretical model results agree with
observations.
150
VERIFICATION OF 1-DAY FLOOD FORECASTS FOR
SINGAPORE
Chien-Wan THAM
National Environment Agency, NEA, Singapore
[email protected]
ABSTRACT
Singapore is a small city island of about 638 square kilometre and lies just north of the
equator at 1.3°N and 103.8°E. Due to its geographical location and its exposure to the maritime, its
climate is characterised by uniform temperature and pressure, high humidity, and abundant rainfall.
The climate of Singapore can be divided into two main parts, the northeast monsoon season and
the southwest, separated by two short inter-monsoon periods.
During the northeast monsoon season in December, northeast winds, which can sometimes
reach a speed of 20 km/h, prevail. These are often accompanied with cloudy conditions and
frequent afternoon showers; and spells of widespread moderate to heavy rain lasting from 1 to 3
days are common. This is the season that Singapore usually experiences flash floods.
From the operational point of view, a period of few hours is the earliest lead time in which
advisories and warnings of heavy rain leading to flash flood can be issued. This is done primarily
through real-time monitoring of local rain gauges, radar images, and geostationary satellites.
Last year, NEA has implemented the mesoscale model Weather Research Forecast (WRF)
Model, which is developed by U.S. National Oceanographic and Atmospheric Administration
(NOAA), for daily operational rain forecast in Singapore. Our implementation has a regional
coverage that is centred on Singapore, configured with a resolution of 20 km and 1 hourly time step.
We have implemented a lightweight verification system upon WRF, a model called
Systematic Objective Area Prediction (SOAP). SOAP is an automated system that infers rain area
coverage for Singapore for the next day in 3 hours blocks; and is coupled with a live validation
system that utilized our Changi Radar Plan Position Indicator images. Operational since middle of
2007, SOAP has verified to have a high average score of above 70%, using a scale score that is
compatible to our office manual forecasting scoring system.
In the Dec of 2007, during the northeast monsoon season period, we have experimented to
use SOAP to predict for rains that are heavy enough to lead to flash floods within Singapore. In all
of the cases of flood reports issued by our local police, the flood events are all preceded with a one
day SOAP prediction of heavy rain. These verification results gave added confidence to the
potential of using SOAP for floods and heavy rain outlook a day ahead, during our northeast
monsoon seasons.
151
QUANTIFYING DYNAMICAL PREDICTABILITY:
THE PSEUDO-ENSEMBLE TECHNIQUE
Wen-wen TUNG1 and Yi-Chi WANG1, Jianbo GAO2
1
Department of Earth and Atmospheric Sciences, Purdue University, IN, USA
Email: [email protected]
2
Department of Electrical and Computer Engineering, University of Florida, FL, USA
ABSTRACT
One may regard atmospheric phenomena over a wide range of spatial and temporal scales,
such as (and most notably) the monsoons, as dynamical systems in which their future states evolve
from their present states according to physical laws or mathematical rules. The dynamical
predictability of the phenomena is defined as the extents to which these systems can be predicted if
an optimum procedure is used. Since the pioneering works of Lorenz, it has been widely recognized
that in order to quantify the sensitive dependence of a model prediction on initial errors, model
imperfections, and external forcing, a probabilistic framework is required. Hence, the ensemble
model technique is widely used, for example, in numerical weather predictions and climate
projections.
In this talk, we examine the current approaches to evaluate predictability using the
ensemble technique, which can be divided into the dynamical and the statistical approaches. We
then uncover connections between the two approaches, which lead to a unified approach based on
the dynamical system and information theories. Furthermore, in the current ensemble framework,
one can easily monitor the model error growth in simple models by using a large number of
ensembles. However, when the models become increasingly complicated, one would only be able
to afford a few ensembles, each with only a small number of members, thus sacrificing estimation
accuracy of the predictions. To improve the accuracy, and more importantly, to expedite
computations, we propose a novel technique for constructing a large number of "pseudo"
ensembles from one single realization. Applications of the pseudo-ensemble technique will be
demonstrated using models with a wide range of complexity, including the Lorenz '96 model. In the
real case of a south-Asian monsoon depression, the Advanced Research Weather Research and
Forecasting (ARW) model is used.
152
MODELLED CHANGES TO SUB-SEASONAL EXTREMES OF
PRECIPITATION AND ACTIVE-BREAK CYCLES OF THE SOUTH
ASIAN MONSOON AT DOUBLED CO2
Andrew TURNER and Julia SLINGO
National Centre for Atmospheric Science, Walker Institute for Climate System Research,
University of Reading, UK
ABSTRACT
This study examines intraseasonal monsoon behaviour in 100-year control and 2xCO2
integrations of the Hadley Centre coupled model HadCM3. In the climate change scenario, mean
summer monsoon rainfall increases, especially over north-central India. Upper percentiles of
extreme precipitation are also found to increase strongly in these regions, beyond changes in the
mean alone. The chance of reaching particular levels of heavy precipitation is found to
approximately double over northern India. The spatial pattern of such changes is however
dependent on the response of the mean monsoon in a given model to anthropogenic greenhouse
warming.
The maximum increase in precipitation intensity over India measured in this model is found
to be remarkably predictable based on purely thermodynamic arguments relating the degree of
atmospheric warming and associated increases in specific humidity. These arguments are tested in
other coupled models contributing to the IPCC AR4.
Active-break cycles of the Indian monsoon, whose timing, strength and duration can be
critical for agriculture, are found to intensify against the seasonal cycle in this study. However no
changes to their frequency or duration are noted.
153
A NUMERICAL STUDY ON THE WIND-TERRAIN INTERACTION
IN THE SOUTH AND SOUTHEAST ASIAN MONSOON REGION
Zhuo WANG1, C.-P. CHANG1, Bin WANG2
1
Department of Meteorology, Naval Postgraduate School, Monterey, California, USA
2
Department of Meteorology, University of Hawaii, Honolulu, Hawaii, USA
ABSTRACT
Numerical simulations with a regional climate model are carried out to explore the roles of
wind-terrain interaction in the circulation and precipitation in the South and Southeast Asian
monsoon regions. In the control run, heavy precipitation is anchored on the windward side of the
terrain, which is consistent with observations. In the sensitivity tests, topography is systematically
removed, and precipitation spreads over a broad area, but maximum precipitation is reduced and
the westerly monsoon flow is weakened. Analysis of the results suggests a positive interaction
between the convection induced by the wind-terrain interaction and the westerly monsoon flow.
The control run simulates the gross features of the observed monsoon transition reasonably
well. The summer monsoon onset first occurs in the Indo-China Peninsula in late April and early
May. It then extends westward to the Bay of Bengal and eastward to the SCS in mid May, and the
Indian monsoon onset occurs in late May. In the sensitivity tests, as topography is removed, the
monsoon onset over the Indo-China peninsula is significantly delayed while the onset time of the
Indian monsoon is nearly unchanged. This suggests that the monsoon onset over the Indo-China
peninsula is triggered by the wind-terrain interaction while the Indian monsoon onset is mainly
controlled by the land-sea thermal contrast.
154
EFFECT OF ENSO ON
WINTER MONSOON AFFECTING HONG KONG
M.C. WU and W.H. LEUNG
Hong Kong Observatory, 134A, Nathan Road, Kowloon, Hong Kong SAR, China
ABSTRACT
Under the dominance of the winter monsoon, cold weather persisted over southern China
from late January to mid February 2008. In Hong Kong, the minimum temperatures recorded at the
Hong Kong Observatory stayed below 12 degrees Celsius for 24 days consecutively, making it the
longest cold spell in Hong Kong since 1968. The effect of La Niña on winter monsoons affecting
Hong Kong once again attracted attention as both 1968 and 2008 were La Niña years.
This study reviewed the characteristics of the winter monsoon and the associated weather
conditions in Hong Kong during ENSO years since 1950. Statistical analyses were carried out to
investigate the relationship between ENSO and local parameters such as mean temperatures, cold
spell duration and number of cold days in winter in Hong Kong. Against a background of global
warming and local urbanization, it was found statistically significant that Hong Kong tends to see a
cooler (warmer) winter during La Niña (El Niño) years. Similar analyses carried out for the Unified
Monsoon Index over southern China suggested that the winter monsoon tends to be stronger
(weaker) during La Niña (El Niño) years, in line with the effect of ENSO to temperature variation in
Hong Kong. The physical basis associated with the phenomenon is also explored by examining the
anomalies in the synoptic patterns during ENSO years.
155
ROLE OF EQUATORIAL CENTRAL PACIFIC AND NORTHWEST
OF NORTH ATLANTIC 2-METER SURFACE TEMPERATURES IN
MODULATING INDIAN SUMMER MONSOON VARIABILITY
Ramesh Kumar YADAV
Indian Institute of Tropical Meteorology
Dr. Homi Bhabha Road, Pashan, Pune 411 008, Maharashtra, India
Email: [email protected]
ABSTRACT
The interannual variability of Indian summer monsoon rainfall (ISMR) have been examined
in association with the variability of 2-meter surface temperature (2mST), and lower- and uppertropospheric pressure and wind patterns over the globe using ERA-40 reanalysis dataset. The
analysis of 44-years (1958-2001) data reveals a recurrent negative phase of ENSO (La Niña)
pattern. The increase in 2mST over tropical southwest Pacific and intensification of subtropical
westerly jet stream over Indian Ocean due to the consequence of thermal wind balance. The
intensification of jet forms anticyclonic anomaly which intensifies Mascarene High as the
atmospheric response is equivalent barotropic over there. The Mascarene High intensifies the cross
equatorial flow and hence Indian summer monsoon (ISM) circulation. While, during non-ENSO
years data reveals a recurrent positive relationship of ISMR with 2mST anomaly over northwest of
North Atlantic and intensification and shift of North Atlantic westerly jet stream to higher latitudes.
The jet stream intensifies the meridional vorticity dipole, formed due to Azores High and the
entrance of Asian subtropical westerly jet stream over North Atlantic and west Mediterranean Sea.
A wave activity flux for stationary Rossby waves diverges out of the vorticity dipole toward
downstream along the Asian jet stream over the Eurasian region. The jet stream acts as a wave
guide and the successive trough and ridges of the Rossby waves travel along the jet and influence
upper-tropospheric Tibetan High and hence ISM circulation.
Key words: Rossby wave, Azores High, ENSO, Circumglobal Teleconnection, Indian Summer Monsoon, Indian Ocean
Dipole Mode
156
DIFFERENT VARIABILITY OF MIXED-LAYER HEIGHTS BEFORE
AND AFTER MONSOON ONSET OVER THE NORTH AND
SOUTH OF SOUTH CHINA SEA IN 1998
YU Xiaoli, WANG Dongxiao, XIE Qiang
Key Laboratory of Tropical Marine Environmental Dynamics, South China Sea Institute of Oceanology,
Chinese Academy of Sciences, Guangzhou, 510301, China
E-mail: [email protected]
ABSTRACT
Based on the GPS radiosonde balloon data observed on R/V “kexue” and R/V “shiyan3”
launched at four times a day in May and June of 1998, the evolution and growth of the mixed-layer
heights were analyzed. The mixed-layer in the boundary layer is defined as the lowest level where
virtual potential temperature remains the same from the surface. the mixed-layer height here is in a
criterion of 1 K statically, the results were as follows: The mixed-layer height in South SCS didn‟t
decrease as a small SST increase after the break of the Asian Monsoon, while the mixed-layer
height in North SCS decrease as the SST falls after the break of the monsoon, The development of
mixed-layer is driven by the surface heat flux and the internal dynamics of the atmosphere. The
air-sea temperature difference is the direst factor of affecting the mixed-layer height, which supports
the water vapor transmit. In the lower atmosphere, the coupled of the mixed layer and the cloud
layer is another reason: if the mixed-layer heights are greater than those of the LCL, thereby
implying saturation in the upper portion of the mixed layer, which makes the MLH didn‟t change; if
the mixed-layer height is lower than that of LCL, there is a possibility of decoupling of the mixed
layer with clouds. therefore in NSCS, the coupled of the mixed layer and cloud layer , the decrease
of the SST caused the mixed layer height decrease, and the decrease of the MLH represent the
release of the energy ,and finally in the form of the rainfall.
Key words: monsoon onset, mixed-layer height, atmosphere internal dynamics
Acknowledgements: This work was supported by the Key Laboratory of Tropical Marine Environmental Dynamics under
fund U0733002, the data was provided by SCSMEX.
Corresponding author: WANG Dongxiao . Key Laboratory of Tropical Marine Environmental Dynamics South China Sea
Institute of Oceanology, Chinese Academy of Sciences164 West Xingang Road, Guangzhou 510301, China
157
INTRASEASONAL VARIABILITY OF LATENT HEAT FLUX IN
THE SOUTH CHINA SEA
Lili ZENG3, Dongxiao WANG
Key Laboratory of Tropical Marine Environmental Dynamics, South China Sea
Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, 510301, China
ABSTRACT
Intraseasonal variability of latent heat in the SCS is examined by using over 9 years
(January 1998 to December 2006) of weekly data. This is done mainly using the harmonic analysis
and composite analysis. In this paper, some fundamental features of the intraseasonal variability
associated with latent heat in the SCS are described in detail. The typical period of such cycles is
6–7 weeks (about 44 days), comparable with the timescales of atmospheric intraseasonal
variabilities in the region. Active monsoon are clearly correlated with positive and negative phases
of intraseasonal variability of latent heat in the SCS. The results demonstrate that characteristics of
intraseasonal latent heat variations in summer are remarkably different from those in winter. It has
potentially important implication that the monsoonal air-sea interaction in summer is somewhat
different from that in winter. The amplitudes of significant intraseasonal oscillations are about 35 W
m-2 and 80 W m-2 are found in summer and winter monsoon, respectively. In summer, the spatial
pattern of intraseasonal latent heat perturbations is characterized by weak eastward (about 1°/day)
and northward (about 0.65°/day) propagation. In contrast, it appears to be trapped in the northern
SCS region without any propagating signal in winter. In addition, intraseasonal latent heat
fluctuations are highly related to wind speed (U) and sea surface specific humidity (Qs). However,
they are primarily associated with near surface air humidity (Qa) in winter.
3
Corresponding author: Lili Zeng, Key Laboratory of Tropical Marine Environmental Dynamics, South China
Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou 510301,
China
E-mail: [email protected]
158
COMPARING OCCURRENCES AND VERTICAL STRUCTURES
OF HYDROMETEORS BETWEEN EASTERN CHINA
AND INDIAN MONSOON REGION
USING CLOUDSAT/CALIPSO DATA
Yali LUO, Renhe ZHANG, Hui WANG
State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China
ABSTRACT
Seasonal variations in the occurrence frequency, vertical location, and radar reflectivity
factor (dBZ) of hydrometeors covering the eastern China and the Indian monsoon region are
described using two CloudSat standard products (GEOPROF and GEOPROF-LIDAR) during the
period of July 2006-August 2007. The 14-month averaged hydrometeor occurrence frequency is
80% (the eastern China) and 70% (the Indian region), respectively, to which multi-layer (mostly
double or triple layers) hydrometeors contribute 37% and 47%. A significant increase in the
multi-layer hydrometeor amount from winter to summer at the Indian region causes a pronounced
seasonal variation in its total hydrometeor amount. The nearly opposite phases in the seasonal
variations of single- and multi-layer hydrometeor amounts result in little change with season in total
hydrometeor amount at the eastern China. Although the passive sensor-based satellite cloud
product is able to provide the major seasonal features in the hydrometeor occurrence frequency
(HOF) as revealed by the CloudSat/CALIPSO product, it generally underestimates the HOF.
The maxima in the amounts of both high-level and thick hydrometeor layers occur during
summer at both regions reflecting impacts of the Asian summer monsoon. The abundance of
low-level cloud layers and scarce of hydrometeors at higher levels at the eastern China during
autumn to winter reflects general subsidence motion at middle and upper troposphere. The
hydrometeors are geometrically thin at both regions. Cirrus containing small ice crystals is the most
common cloud type at the Indian region all over the year, while the eastern China hydrometeors are
located lower and distributed more evenly in the dBZ-altitude phase space. Although the Indian
region has deeper convection and more anvils than the eastern China during summer, the
dBZ-altitude frequency distributions of deep convection and anvils are nearly identical between the
two regions.
201
IMPACT OF INTERACTION OF TYPHOON AND SUMMER
MONSOON ON INDUCED TORRENTIAL RAIN
CHENG Zhengquan1, CHEN Lianshou2, LI Ying2
1
Guangzhou Central Meteorological observatory, Guangzhou, China
2
Chinese Academy of Meteorological Sciences, Beijing, China
ABSTRACT
Landfalling typhoons would result in various disasters, such as strong winds, rainstorms and
storm surges, which always diminish with the decay of typhoons due to the cutoff of latent heat from
the sea surface after landfall. While under favorable conditions some tropical cyclones, even
tropical depressions, could bring extra-heavy rain events continuously and lead to a calamity.
Besides typhoons, summer monsoon is another system to produce torrential rain processes in rainy
season in South China. When a landfalling typhoon encounters the onset of summer monsoon, a
disastrous rainstorm always would occur. The No.0604 tropical cyclone BILIS is the typical case.
Based on Tropical Cyclone Yearbooks, NCEP/NCAR reanalysis data and the dynamic
composite analysis, the large-scale circulation characteristics are analyzed of two kinds of
typhoons , strong-rainfall and weak-rainfall typhoons, with similar track and intensity but distinct
rainfall intensity in 48 hours after landfall. Result shows that, the transportation of vapor in the
southwestern stream is crucial to typhoon rainfall. A deep southwestern jet usually connects with
the strong-rainfall typhoon for a long time even after its landfall. The transfer of sensible and latent
heat from the southwestern monsoon jet shows distinct characteristics between to the
strong-rainfall typhoons and to the weak-rainfall typhoons.
In addition to diagnostic analysis, a control experiment and several sensitivity experiments
are designed to study the impact of interaction between a typical tropical cyclone BILIS(0604) and
summer monsoon on the induced rainstorm based on the WRFV2.1.2 model and NCEP data. The
result of the control experiment reveals that the horizontal transfer of moisture from the boundaries,
especially from the southern boundary, is crucial to the torrential rain process, which is favorable to
the maintenance of the cyclonic structure of BILIS and the induced rainstorm due to the emission of
latent heat. The sensitivity experiment without the transfer of moisture from the southern boundary
suggests that the diminishing vapor in the domain of BILIS results in the transformation of its
structure from the cyclonic circulation to a shear shape and a distinct decrease of precipitation not
only in coverage but also in intensity. Furthermore, the summer monsoon jet is another important
factor to affect the rainstorm. In the experiment where the wind velocity in the southwestern
monsoon channel is weakened, the vapor flux transferred to BILIS circulation becomes less
accordingly and the intensity and coverage of rainstorm decrease. Strong summer monsoon
activities also can bring rainstorms even without cooperation of a tropical cyclone. In another
experiment BILIS circulation is removed to study the effect of BILIS itself in the extreme process.
Result proves that not only the tropical cyclone strengthens the transfer of moisture by its strong
wind, but also its movement changes the distribution of moisture and instability energy transported
from the monsoon jet. Moreover, the unique structure of a tropical cyclone, strong convergence at
lower level and divergence at upper level, is a dynamo to produce torrential rain events.
202
THE ARCTIC OSCILLATION AND THE AUTUMN/WINTER SNOW
DEPTH OVER THE TIBETAN PLATEAU
Jun-Mei LÜ1, 3, Jian-Hua JU2*, Seong-Joong KIM3,
Ju-Zhang REN4, Yu-Xiang ZHU2
1
Chinese Academy of Meteorological Sciences, Beijing, China;
China Meteorological Administration Training Centre, Beijing, China;
3
Korea Polar Research Institute, Incheon, Korea;
4
Yunnan Institute of Meteorology, Yunnan, China
2
ABSTRACT
The present study examines the relationship between the Arctic Oscillation (AO) and the
autumn/winter snow depth over the Tibetan Plateau. Results show that there exists significant
correlation between the AO and the Tibetan Plateau snow depth on interdecadal time scale. The
AO and the snow depth over the Tibetan Plateau experienced interdecadal regime shift in the late
1970‟s. Before the late 1970‟s when the AO was in its interdecadal negative phase, the snow depth
over the Tibetan Plateau increased in fall and then decreased in following winter. Conversely, when
the AO has entered its interdecadal positive phase since the early 1980‟s, the snow depth
decreased in fall, but increased in winter. The vertical propagation of Rossby waves is proposed to
explain the physical process linking the AO with the snow depth. Anomalously excessive fall snow
depth over the Tibetan Plateau amplifies orographically forced upward stationary waves. The
snow-forced changes in stratosphere are not identified until later in the winter season when Rossby
waves propagate into the stratosphere and the AO becomes negative. In winter, when the
troposphere and stratosphere are actively coupled, the downward propagation of Rossby waves
associated with the positive AO phase modulates the atmospheric circulation in the troposphere,
and causes the abnormal increase of snow depth over the Tibetan Plateau.
Acknowledgments: This investigation was jointly supported by and the National Natural Science Foundation of China
under Grant No.40705026 and No.40675056, The Climate Change Special Project of China Meteorological
Administration (Grant No. CCSF2006-14), and Project of Integrated Research on the Composition of Polar Atmosphere
and Climate Change (COMPAC) of Korea Polar Research Institute (PE08030)
*
Corresponding Author: Jianhua Ju (email: [email protected])
203
ASIAN-PACIFIC OSCILLATION AND ASSOCIATED ASIAN
CLIMATE VARIABILITY
Ping ZHAO1, Junming CHEN1, Yan ZOU1, Sulan NAN1, Botao ZHOU2
1
Chinese Academy of Meteorological Sciences, Beijing, China
2
National Climate Center, Beijing, China
ABSTRACT
The Asian-Pacific Oscillation (APO) is a zonal teleconnection pattern over the extratropical
Asian-Pacific region, reflecting an out-of-phase relationship in variability of the eddy temperature
between Asia and the North Pacific. Its formation is associated with an extratropical zonal vertical
circulation in the troposphere of the Northern Hemisphere during summer. Through this zonal
circulation, an anomaly of heating over the Asian land contributes to the formation of the APO. The
numerical simulations show the Tibetan elevated heating exerts influence on the atmospheric
circulation over other extratropical areas of the Northern Hemisphere while the Pacific sea surface
temperature has no pronounced effects on the APO pattern.
The APO index shows a decadal variation, tending to be in a high-index phase before 1975
and in a low-index phase afterward and has a quasi-5-yr period. With higher APO-index conditions
in the upper troposphere, the summer South Asian high and the North Pacific trough are stronger,
while the westerly jet stream over Asia and the easterly jet stream over South Asia strengthen. Also,
the Asian low and the North Pacific subtropical high are stronger in the lower troposphere. The
anomalous southerlies prevail at the midlatitudes of East Asia, accompanied by a more northward
Mei-yu front, and the anomalous westerlies prevail over South Asia. Summer rainfall increases in
North China, South China, and South Asia, while it decreases from the valley of the Yangtze River
to southern Japan, and near the Philippines. Moreover, the variability of the APO has a significant
positive correlation with the tropical cyclones over the western North Pacific during summer. Under
higher-index conditions, there are more tropical cyclones over the western North Pacific and the
tropical cyclones tend to occur more northward.
204
APPLICATION OF GRAPES REGIONAL MODEL IN SEVERE
WEATHER FORECASTING
Xindong PENG
The state key laboratory of severe weather, Chinese Academy of Meteorological Sciences, CMA
[email protected]
ABSTRACT
Severe weather in concerning with the Meiyu front and Typhoon is the most important
phenomena in China, especially in southeastern China. Heavy rainfall with strong wind usually
conduces to severe disaster. We have make use of the regional numerical model, which has been
developed at CMA, to do numerical forecast in Southeastern China and Northern China. The
numerical product is also used for weather forecasting during the Beijing 2008 Olympic Games.
The output of a global spectral model T213 is used as the environmental field of the regional
GRAPES. Surface (include AWS) and ship observations and soundings are used in the 3DVAR
system to refine the model initial data. Rolling prediction is carried out eight times every day in a
horizontally 0.12-degree spacing configuration.
Two cases will be shown in this paper. One is the case in the middle of June before the
Meiyu rainy season. Mesoscale convective systems embedded in a front cause a heavy rainfall at
the southeastern China. Active southwesterly in the monsoon area acts as an important transporter
of water vapor, which interact with a low system in South China and the western North Pacific
subtropical high. The model results show a quasi-static rain band along the continental line during
12-14 June 2008, which according with the observation. Another case shows a large Typhoon that
landed at Fujian on 28 July after its going through Taiwan previously. The structure is well simulated
in the model with a heavy rainfall area being located in the southeastern part. Analysis and
numerical results in detail will be shown in this presentation.
Both frontal rainfall and Typhoon are the main severe weather in summer monsoon system
in China. The analysis and forecasting of these systems help us to evaluate the model ability and to
improve the model dynamics and physics.
205
WEAKENING OF THE EAST ASIAN SUMMER MONSOON
IN AN ACCELERATED WARMING ENVIRONMENT
AFTER THE LATE 1980S
Bingyi WU1, Renhe ZHANG1, Yihui DING2 and Rosanne D’ARRIGO3
1
Chinese Academy of Meteorological Sciences, Beijing, China
2
National Climate Center, Beijing, China
3
Tree-Ring Laboratory, Lamont-Doherty Earth Observatory, Palisades, New York, USA
ABSTRACT
Observational analysis revealed a weakening trend of a dominant mode (M21) of the East
Asian summer monsoon (EASM) variability in recent decades. A persistent weakening of the EASM
mode has occurred in the late 1980s with a coherent negative phase since the early 1990s. The
persistent weakening of the EASM mode that occurred in the late 1980s can be attributed to an
accelerated warming environment characterized by spring increasing sea surface temperature
(SST), reduction of spring Arctic sea ice and Eurasian snow cover, and the spring weakened
land-sea thermal contrast. Accompanying the persistent weakening of the EASM mode, especially
after the early 1990s, significantly increased summer precipitation can be observed in South China
with decreased summer precipitation in north and northeast China. Although the weakening of this
EASM mode can well explain summer precipitation anomalies in South China after the late 1980s it
cannot be as the reason being responsible for summer precipitation anomalies in South China
during the period before the late 1970s.
206
TORRENTIAL RAINFALL MECHANISMS OF SEVERE TROPICAL
STORM BILIS (2006) AFTER ITS LANDFALL
Shuanzhu GAO1, Zhiyong MENG2, Fuqing ZHANG3, Lance F. BOSART4
1
China National Meteorological Center, Beijing, China
Department of Atmospheric Sciences, School of Physics, Peking University, Beijing, China
3
Department of Meteorology, the Pennsylvania State University, USA
4
Department of Atmospheric Sciences, University of Albany, USA
2
ABSTRACT
This observational study examines dynamical mechanisms that lead to torrential rainfalls
and severe flooding over large areas of south China induced by Bilis, a western Pacific severe
tropical storm that made landfall at the southeast coast of China on 13 July 2006 with remnant
circulation persisted over land until after 18 July 2006. The heavy rainfalls associated with Bilis
during and after its landfall may be divided into three stages. The first stage of the rainfall, which
occurs in Fujian and Zhejiang provinces, is directly induced by the inner-core storm circulation
during its landfall. The third stage of rainfall, which occurs along the coastal areas of Guangdong
and Fujian provinces, likely resulted from the interaction between Bilis and the South China Sea
monsoon enhanced by topographical lifting along the coast.
The second stage of the rainfall, which causes the most catastrophic flooding and is the
primary focus of the current study, occurs inland near the border regions between Jiangxi, Hunan
and Guangdong provinces. Using the final (FNL) analyses of Global Forecasting System (GFS) of
National Centers for Environmental Prediction (NCEP) and Weather Research and Forecasting
(WRF) model, the possible contributors to the second stage rainfall are examined. The result shows
that this stage of the rainfall is well collocated with a rich moisture convergence and favorable
instability conditions along with sufficient lifting from warm advection, topography, vortex-vertical
shear interaction, and attendant frontogenesis.
207
DECADAL RESEARCH REVIEW ON THE UNDERSTANDING
OF THE ASIAN MONSOON SYSTEM
QIAN Wei-hong
Department of Atmospheric Science, Peking University, Beijing, China
E mail: [email protected]
ABSTRACT
This paper is a decadal research review on the understanding of Asian monsoon system
starting from the South China Sea Monsoon Experiment (SCSMEX) in 1998. During the last decade,
new progresses of onset and evolution were achieved not only from the South China Sea (SCS)
summer monsoon but also from the South Asian monsoon and the East Asian summer monsoon in
the whole Asian region. Before decade, less acknowledge on the SCS summer monsoon is due to
lack of observation in the Southeast Asian region. However, a famous achievement was proposed
by Chinese scientists. There are two monsoon systems in the South Asian and the East Asian
regions, which are “connection” and “independence” of each other. After the SCSMEX, regional
onsets of rainy seasons were revealed. In the south of the middle-lower Yangtze River (Jiangnan),
the subtropical rainy season starts from early April. In the Indo-china peninsula (ICP), the summer
half-year rainy season begins from late April while the central SCS rainy season is rapidly onset on
middle May. As the onset of the central SCS summer monsoon, an advance northward is widely
observed from South Asia, the east part of the Tibetan Plateau, East Asia and the Northwest Pacific
region. A dry-wet transition of half-year spell is found in the subtropical Jiangnan, the ICP, and the
central SCS regions, respectively. The summer monsoon onset in the central SCS region results
first from any one or two rainfall advances of South China, the ICP, the east part of Philippine
Islands, and the south part of the SCS, respectively. Through the updated observational data and
renew analyzed idea, how many independence sub-monsoon systems have been examined and
their connections have been understood in detail. On the planetary scale over the region of the
Tibetan Plateau, the Asian continent, the Indian Ocean and the Pacific, two independence
monsoon systems in South Asia and East Asia are centered by the heat depression over the
plateau. Regional sea-land thermal contrasts surrounding the Asian continent form six
sub-monsoon systems with their monsoon depressions and rainfall. These systems are named
locally by the Southwest Asian (Arabian Sea) tropical summer monsoon, the South Asian (the Bay
of Bengal) tropical summer monsoon, the Southeast Asian (SCS) tropical summer monsoon, the
Northwest Pacific tropical summer monsoon, and the East Asian subtropical summer monsoon. In
spring, there are three monsoon systems in the Asia-Pacific region. In the east part of the plateau, a
topographical reversed trough is referred to as the spring monsoon system with its rainfall first
starting in the east part of South China since middle March and then extending westward. Stable
spring rainfall in the South Asia (Bay of Bengal) prevails over the regional monsoon depression
from middle April without the rainfall in the winter season. The seasonal precipitation along the East
Asian trough near Japan can be observed from winter to spring. In the winter season, two short
spells of precipitation occur in the pentad 5 and pentads 9-12 near the topographical reversed
trough along the Jiangnan region.
Keywords: Tropical monsoon, subtropical monsoon, South Asia, East Asia, Northwest Pacific, review
208
FEATURES OF LOW FREQUENCY OSCILLATION FOR
MOISTURE TRANSPORT DURING TYPICAL DROUGHT/FLOOD
YEARS OVER YANGTZE-HUAIHE BASIN
LIANG Ping1, CHEN Longxun2, HE Jinhai3
1
Shanghai Climate Center, Shanghai, China
Chinese Academy of Meteorological Sciences, Beijing, China
3
Nanjing University of Information Science & Technology, Nanjing, China
2
ABSTRACT
Using daily NCEP/NCAR reanalysis dataset and observational rainfall data from China for
the 1971-2000 period, the characteristics of low-frequency oscillation (LFO) for moisture transport
and its relations with rainfall during typical drought/flood years over Yangtze-Huaihe basin are
analyzed. Results are as follows.
Intraseasonal variation of rainfall amount over the Yangtze-Huaihe basin exhibits notable
30~60d low frequency oscillation during typical flood years but the contrary is true during typical
flood years. And obvious LFO exists in meridional moisture transport over the middle and lower
reaches of the Yangtze River during flood year while that is unnoticeable during drought year.
As for transportation of LFO over subtropical Asia, LFO of meridional (zonal) moisture
transport along 32.5°N（25°-30°N）may stem from the north-middle Pacific and propagate to 100°E,
but the propagation of moisture transport from the north-west Pacific to southeastern China has
important impacts on the violent LFO and its relating rainfall over the region. Over 110°-120 °E, LFO
of moisture transport flux convergence spreads northward from the South China Sea to 40°N and is
accompanied by the northward shift of the rainfall belt over eastern China during typical flood year.
As far as typical drought year is concerned, LFO of moisture transport without distinct meridional or
zonal propagation exhibits local activity feature either over tropics or over sub-tropics.
On the specific relationship between LFO of moisture transport and rainfall over
Yangze-huaihe basin, the anti-cyclonic low-frequency moisture transport circulation over the west
Pacific triggered by the northward propagation of cyclonic low-frequency circulation from the tropics
interacts with the moisture transport from the north of Yangze-huaihe basin, which is corresponding
to more rainfall during Meiyu period. On the contrary, inactive low-frequency perturbation without
northward propagation and anti-cyclonic low-frequency moisture transport circulation over the west
Pacific westward propagation may attribute to anomalously less rainfall during Meiyu period.
Key words: moisture transport; low frequency oscillation; drought/flood; Yangze-huaihe basin
209
THE IMPACT OF INTRASEASONAL OSCILLATIONS ON THE
ONSET AND INTERANNUAL VARIATION OF THE INDIAN
SUMMER MONSOON
Yanjun QI1, 2, 3, Renhe ZHANG*2, Tim LI4, Min WEN2
1
Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China
3
Graduate University of Chinese Academy of Sciences, Beijing, China
4
International Pacific Research Center and Dept. of Meteorology, University of Hawaii at Manoa, HI, USA
2
ABSTRACT
The role of the intraseasonal oscillation (ISO) on the seasonal and interannual variations of
the Indian summer monsoon is investigated based on the analysis of observational data. It is shown
that the ISO significantly contributes to the establishment of low-level westerlies during the
monsoon onset and developing period. The effect of the ISO on the annual cycle of the monsoon is
through nonlinear eddy momentum transport. On the interannual timescale, the Indian summer
monsoon rainfall exhibits a significant out-of-phase relationship with the ISO intensity over the
Indian monsoon region. The weaker the Indian summer monsoon, the stronger the ISO intensity is,
and vice versa.
Key words: Intraseasonal Oscillation (ISO), Indian summer monsoon
210
CHARACTERISTIC OF MESOSCALE CONVECTION SYSTEM
AFTER THE LANDFALL OF TYPHOON BILIS
CAI Ronghui1, LIU Zhixiong2, HUANG Xiaoyu3, QU Youming1
1
HuNan Meteorological Research Institute, China
LouDi the meteorological bureau of HuNan China
3
HuNan Provincial Meteorological Observatories, China
2
ABSTRACT
Using the FY2C infrared satellite cloud image、the water vapor image and TBB data, it was
analyzed that the characteristic and the structural evolution of the mesoscale convection system
before or after strong tropical storm Bilis landed . And using the high resolution mesoscale
numerical model(WRF) , it was simulated that structural evolution of the mesoscale convection
system in low pressure rainstorm in Zhejiang, Fujian, Jiangxi specially in Guangdong, Hunan
province after the Bilis landed. it was Analyzed that the impact of mesoscale convective systems
about typhoon moving westward in the process of changing the shape. The results show that: by
the interaction of southwest air flow of the subtropical high, the South China Sea monsoon and the
southeast circulation of the typhoon low pressure, a mesoscale disturbance had happened in the
macroscale low-level jet which located on the southeast side of the typhoon low pressure, also
named the mesoscale low jet disturbance, and there was strong convergence and lifting movement
on its left-front side , the mesoscale high-level jet was produced in high lifting updraft region, and
strong divergence happened on the right posterior side. Because of the strong perturbation, strong
convergence and strong Vapor flux transport of the macroscale low-level jet, it caused that the
mesoscale convection system was produced which located at the southeast side of typhoon low
pressure, there was the very good corresponding relations with the live precipitation distribution.
Keywords: Landfalling typhoon; South China Sea monsoon; Mesoscale convection system; Mesoscale high jet；Typhoon
shape
211
DELAYED IMPACT OF THE EL NIÑO EPISODES IN THE
CENTRAL PACIFIC ON THE SUMMERTIME CLIMATE
ANOMALIES OF THE EASTERN CHINA IN 2003 AND 2007
BAO Ming1, 2, HAN Rongqing3
1
Center for monsoon system research, Institute of Atmospheric Physics, CAS, Beijing, China
2
Department of Atmospheric Sciences, Nanjing University, Nanjing, China
3
National Climate Center, Beijing, China
ABSTRACT
In 2003 and 2007, the eastern China suffered similar summertime climate disasters with
severe floodings in the Huaihe River valley and hot wave in Southern Yangtze River delta and
South China. Using sea surface temperature (SST) data and outgoing longwave radiation (OLR)
data from the National Oceanic and Atmospheric Administration (NOAA) and reanalysis data from
the National centre for Environmental Prediction/National Centre for Atmospheric Research
(NCEP/NCAR), the 2002/03 and 2006/07 El Niño episodes and the anomalous subtropical
circulation in East Asia were analysed. Both the moderate El Niño episodes matured in the central
equatorial Pacific during the early winters. The zonal wind anomalies near the sea surface of the
western-central equatorial Pacific excite equatorial Kelvin waves propagating eastward and affect
the evolutions of the El Niño episodes. The subsurface temperature and SST anomalies in the
western equatorial Pacific during the decaying stage have a direct impact on the thermal state of
the western equatorial Pacific. Due to the active convections in the western equatorial Pacific in
early summer and the weak warm SST anomalies in the tropical western Pacific from spring to early
summer, the convection activities in the western Pacific warm pool showed the pattern in which the
anomalous strong convections only appeared over the southern regions of the tropical western
Pacific warm pool, which has effect on the meridional shifts of the western Pacific subtropical high
in early summer. The physical progress of the delayed impact of the El Niño episodes in the central
equatorial Pacific and their decaying evolution on the climate anomalies in the eastern China was
interpreted through the thermal state of the tropical western Pacific warm pool and the response of
the western North Pacific anomalous anticyclone.
Key words: El Niño episodes, impact, climate anomalies, the eastern China
212
ANALYSIS ON APPROACHING DEFLECTION PHENOMENON
OF TYPHOON LANDING AT COAST OF ZHEJIANG, FUJIAN,
AND TAIWAN
CHEN Hongyi, ZHANG Mei, YUAN Hongshen
Taizhou Meteorology Bureau, Zhejiang Taizhou, China
Yuhuan Meteorology Bureau, Zhejiang Yuhuan, China
ABSTRACT
Tropical cyclone (typhoon) often deflects when it is Landing at coast of ZHEJIANG, FUJIAN
AND TAIWAN, studying and grasping this kind of phenomenon rule is very significant for typhoon
extrapolation forecast. According to setting standard, phenomenon of the debarkation typhoon of
approaching deflection is analyzed and calculated, the conclusion that the path of landing typhoon
is overall deflecting left is obtained, and some experiences in extrapolation (path) forecast on
Zhejiang, Fujian, and Taiwan coast debarkation typhoon are listed.
213
PRELIMINARY INVESTIGATION OF THE UNUSUAL
CIRCULATION INDEX DURING LOW TEMPERATURE,
RAIN/SNOW, AND FROST DISASTER
CHEN Hui1, LIU Fenghuai2, LIU Fei3
1
Huai An Academy of Agricultural Sciences, China
2
Huai An Meteorological Administration, China
3
The University of Alabama in Huntsville, USA
ABSTRACT
Since January 10 2008, China, particularly the southern part, has experienced an extended
period of blizzards, hail and frost. Many provinces like Shanghai, Zhejiang, Jiangsu, Anhui, Jiangxi,
Henan, Hubei, Guangdong, Guangxi, and Chongqing have been severely affected. Average
temperature during January to February was 2～4℃ lower than normal; in some regions, the
average temperature dropped more than 4℃ than normal. In January, the average rainfall/snowfall
was generally more than usual; in most regions to the north of Yangtze River, the south of
southeastern, and the western Yunnan area, the precipitation ranges from 50% more ～ twice of
average; some regions even saw more than twice rain. In February, most part of Sichuan and
Chongqing, southern Yunnan area and most part of Guangxi had more rain/snow than usual. To
understand this wide-spread, long-extended unusual low temperature, rain/snow, frost severe
weather condition, this paper analyzes the circulation data since 1951 and has gained some
significant results and facts.
1. From August 2007 to February 2008, SOI remained higher than the same period of time
of previous years and reached 19 in February 2008, which is the all time maximum.
2. From December 2007 to February 2008, Atlantic and Europe pattern E remained higher
than the same period of time of previous years, whereas Atlantic and Europe pattern W remained
lower than the same period of time of previous years.
3. From December 2007 to February 2008, Index of the area of the polar vortex in the
Atlantic and Europe (sector 4, 30W-60E) remained lower than the same period of time of previous
years.
4. From December 2007 to February 2008, the ridge line of the subtropical high over the
western Pacific (110E-150E) remained north to the same period of time of previous years, and
reached 17 in January 2008, which is the all time maximum.
Above results show that Monsoon circulations exhibited some unusual features from the
end of summer to winter; therefore it shows some connection to the wide-spread low temperature,
rain/snow, and frost weather on January 10 2008 in China.
Note:
(1). The circulation data used in this paper is from the Climate Diagnostics and Prediction Division of the National Climate
Center.
(2). The average value in this paper is the average between 1971 and 2000.
214
ANALYSIS AND FORECAST OF THE HUAIHE RIVER BASIN
FLOOD BY USING SUBTROPICAL HIGH ETC. CIRCULATION
INDEX
CHEN Hui WANG Su YU Jihua
Huaian Meteorological bureau, Jiangsu, China
ABSTRACT
Huaihe River Basin was in a serious flood disaster in 2007 and 2003.By analysing
subtropical high etc. circulation index since 2000, the results show that when index of the area and
strength of the Northern Hemisphere subtropical high (5E-360E)、the area of the subtropical high
over the Pacific (110E-115W) and index of Tibetan Plateau（30N-40N、75E-105E）goes stronger
from winter to early spring of next year, index of European E-Atlantic circulation goes weaker from
autumn to early spring of next year, The occurrence of floods in the Huaihe River Basin has a good
relation to those changes. Physical meaning of this result is also relatively clear. Based on this
result, four methods was developed to forecast short-term climate. When one of these methods is
met, Huaihe River Basin flood will occur, and contrarily it will not happen. When using this method
to forecast floods from 2000 to 2008, the success rate is 9/9.There are three methods can be used
in the annual mid-March to mid-April. According to the information, relevant departments can
prepare for flood control so earlier that disaster is reduced to the minimum.
Key words: Huaihe River Basin Flood circulation index Forecast of short-term climate
215
CAUSUALITY ANALYSIS ON A SEVERE CHILLING ICE RAIN
AND SNOW FREEZING DISASTER WEATHER EVENT
IN EARLY 2008 IN GUANGXI
CHEN Ye-guo, NONG Meng-song
Guangxi Meteorological Observatory, Nanning, Guangxi, China
ABSTRACT
Based on the surface observational data and sounding data, the causes of the rare chilling
icy rain and snow freezing disasters event happened during January 12 to February 5 is
analyzed.Results show that the rare lasting and stable abnormal circulation over Eurasian continent
is the direct reason for the extreme event.The abnormality are mainly in the factors as follow. (1)
The favorable circulation background is high-pressure in the west and low-pressure in the east
which is benefit for the strong cold air moving to China. (2) The active tough is the motivation of the
warm and moist air flowing from Tibetan Plateau to China. (3) The invert layer existence in the
mid-low level is the main reason for large range icy rain occurrence.
Key words: Guangxi; chilling icy rain and snow; freezing hazard; causality
216
ANNUAL EVOLUTION OF PRECIPITATION IN FUJIAN
PROVINCE AND ITS RELATION TO EAST ASIAN MONSOON
CHI Yanzhen1, 2, XU Jinjing1, HE Fen1, WEN Zhenzhi1
1
Fujian Climate Center, Fuzhou, China
Nanjing University of Information Science and Technology, Nanjing, China
2
ABSTRACT
Herein the annual evolution of precipitation in Fujian Province and its relation to East Asian
Monsoon are investigated in the context of pentad rainfall from 66 stations in Fujian, day-to-day
gridded reanalysis from NCEP/NCAR, daily OLR( outgoing long-wave radiation ) from NOAA and
CMAP (Climate Prediction Center Merged Analysis of Precipitation) rain data. Results show that the
temporal and spatial distribution of precipitation in Fujian differ greatly from season to season , i.e.
wet season consists of Spring and Summer(from March to September ) while dry season includes
Autumn and Winter(from October to February ). The period of rainfall abruptly increasing( usually at
mid March ) is evidently earlier than the onset of tropical summer monsoon (or SCS summer
monsoon), however, the intensity and northward march to the continent of the latter effect
significantly the intensity and spatial structure of precipitation in Fujian , which is peaking at June.
On the other hand, the annual cycle of the rainfall bears an intimate relation to the subtropical
monsoon with the characteristics of rain belts starting, drifting and retreating, which lies on setting
up step by step but retreating rapidly. We confirm that the conclusions and farther research will be
in an effort to provide a new approach to predicting precipitation in Fujian related to the East Asian
monsoon.
Keywords: Annual evolution of precipitation in Fujian Province; SCS summer monsoon ; East Asian subtropical monsoon
217
STATISTICAL CHARACTERISTICS OF LANDFALLING
TROPICAL CYCLONE RAINFALL REINFORCEMENT
Mei-ying DONG1, 2, 3, Lian-shou CHEN1, Ying LI1
1
Chinese Academy of Meteorological Sciences/LASW, Beijing, China
2
Zhejiang Meteorological Observatory, Hangzhou, China
3
Nanjing University Of Information Science, Nanjing, China
ABSTRACT
According to the evolution of intensity of heavy rainfall, the concept of landfalling Tropical
Cyclone Rainfall Reinforcement (TCRR) is put forward in the paper. Thereafter, the daily TC rainfall
dataset from 1949 to 2006 (except 2002) is used to analyze the statistical characteristics. Results
show that the annual and monthly change of TCRR frequency (intensity) are significant and have a
steady (increase) trend during the past 57 years, where obvious increase for frequency and
intensity in the last decade. TCRR can happen from July to September with the highest frequency in
August and the intensity maximum in July. The high occurrence of TCRR locates in the southern
Guangxi and southern Shandong, and the intensity maximum occur in the eastern Dabie Mountain
in Anhui province. 9.7% landfalling TC can cause the TCRR, in which 83.8% make landfall on the
coastal areas of Zhejiang and Fujian province, displaying three typical tracks as northward,
westward and northwestward motion over land. Both maxima of frequency and intensity appear in
tropical depressions. About 2/3 TCs tend to slow during rainfall reinforcement. The asymmetric
distribution of TCRR maximum relative to TC is prominent, with high probability in the regions of
northeast, southwest azimuths and within 5 degree distance from the TC center.
Key words: statistical characteristics；tropical cyclone；rainfall reinforcement
218
ANOMALOUS WESTERN NORTH PACIFIC MONSOON TROUGH
AND TROPICAL CYCLONE ACTIVITIES
GAO Jian-yun1, ZHANG Xiu-zhi2, JIANG Zhi-hong3, YOU Li-jun
1
Fujian Climate Center, Fuzhou, China
National Climate Center, Beijing, China
3
Nanjing University of Information Science and Technology, Nanjing, China
2
ABSTRACT
A general survey was made of 1979-2005 tropical cyclones (TC) before a sequence is
established of the western North Pacific monsoon trough (MT) tropical cyclones (MTTC). Statistics
show that in May – October, 1979-2005, TCs originating from the South China Sea (SCS) and
western North Pacific (WNP) totaled 672, of which 491 had the origin in the monsoon trough (i.e.,
MTTCs), making up 73.1% of the total and 79.2% of the TCs landing on China in this period. It
follows that grasp of their activity features means the grasp of the main activity laws of WNP and
China-landing TCs. Based on the analysis of day-to-day circulation fields the MTs are categorized
as 1) SCS type, 2) SCS-WNP type, 3) reversal type, 4) triple-flow type and 5) WNP type. In terms of
the strength and position of May to October monsoon troughs, subtropical highs and
cross-equatorial flows on an annual basis, the 1979-2005 monsoon troughs are separated into such
annual types as the southwest- northwest-, and eastward of mean as well as normal. For the first
three MT anomalous annual types diagnostic study is conducted of TC formation favorable SST
and large-scale circulation fields, vapor transport, atmospheric apparent heat sources, apparent
vapor sinks, and zonal wind vertical shear, indicating that for the different MT annual types
differences in Pacific SST fields cause the disparity in the intensity of the Hadley and Walker
circulations, the positions of western Pacific subtropical high and South Asian high as well as the
intensity of cross-equatorial flows, thus producing TC genesis favorable thermal, dynamic and
environmental conditions, leading to remarkable differences in MTTC genesis area, frequency,
track and TC China-landing location.
Key words: western North Pacific, monsoon trough, tropical cyclone, effects
219
PHASE RELATIONS AMONG WESTERN NORTH PACIFIC
MONSOON, INDIAN MONSOON AND AUSTRALIAN MONSOON
Dejun GU1, Tim LI2, Zhongping JI3, Bin ZHENG1
1
Guangzhou Institute of Tropical and Marine Meteorology, and Key Open Laboratory for Tropical Monsoon,
China Meteorological Administration, Guangzhou, China
2
International Pacific Research Center, and Dept. of Meteorology, University of Hawaii at Manoa, USA
3
Guangzhou Central Meteorological Observatory, Guangzhou, China
ABSTRACT
The phase relationships of the SCS/WNP summer monsoon (WNPM) with the Australian
monsoon (AM) and Indian monsoon (IM) are investigated using observational rainfall, SST and
NCEP reanalysis data for the period of 1979-2005. It is found that WNPM has significant lead-lag
phase relationships with AM. A strong WNPM often follows a strong AM but leads a weak AM a half
year later. A significant simultaneous negative correlation appears between WNPM and IM. The
negative correlation coefficient reaches -0.64, exceeding the 99% significant level.
By examining the circulation and SST patterns associated with the in-phase and
out-of-phase relationships, several mechanisms are proposed. The in-phase relationship from AM
to the succeeding WNPM occurs primarily during the ENSO decaying phase. A warm SSTA in the
eastern Pacific induces a reversed anomalous Walker cell and causes a weak AM during El Nino
mature winter. Meanwhile, an anomalous anticyclone is induced in WNP through the Pacific-East
Asia teleconnection and is further maintained through a positive thermodynamic air-sea feedback,
leading to a weakened WNPM.
The out-of-phase relation from WNPM to the succeeding AM involves two different
scenarios: the El Nino early onset and El Nino decaying/La Nina developing. For the first scenario,
a warm SSTA in the eastern Pacific forces a Rossby wave response and low-level cyclonic shear
over WNP, which further enhances WNPM through Ekman-pumping induced boundary layer
convergence. As the SSTA develops toward boreal winter, it weakens the AM through the
anomalous Walker circulation. For the second scenario, the persistence of an anomalous
anticyclone during the El Nino decaying phase leads a weak WNPM. With the onset of La Nina in
the late year, the cold SSTA leads to a strong AM in boreal winter.
The simultaneous negative correlation between WNPM and IM appears during either the El
Nino earlier onset or the El Nino decaying/La Nina developing cases. In the former case, the SSTA
in the eastern Pacific on one hand leads to the cyclonic wind shear and thus a strong WNPM and
one the other hand anomalous subsidence over the Maritime Continent, which further suppress the
convection over India through an atmospheric Rossby wave response. In the latter case, a weak
WNPM results from the persistence of an anomalous low-level anticyclone from boreal winter to the
subsequent summer, whereas a strong IM is caused by a simultaneous cold eastern Pacific SSTA
in JJA, a basin-wide warming in the tropical Indian Ocean prior to the monsoon onset, or enhanced
convection in the Maritime Continent associated with the local Hadley circulation.
220
INTRODUCTION TO GLOBAL BICUBIC NUMERICAL MODEL
(GLO-BINM) AND ITS MATHEMATICAL NUMERICAL ANALYSIS
FOUNDATION — FOR A SIMULATION CASE OF NON-STATIC
AND TOTAL COMPRESSIBLE ATMOSPHERIC EQUATION SET
GU Xuzan
Institute of Heavy Rain, CMA, Wuhan, China
ABSTRACT
In this paper is brought to success Bicubic Numerical Model (BiNM for short), that is with
fitting of cubic curved spline / bicubic curved surface to the meshes discrete, physical fields of the
model atmosphere, and getting their first-order and second-order derivatives, and doing discrete
time integration for the forecast governing equations, and that is with a new algorithm of “bicubic
surface fitting - time step integration - bicubic surface fitting - ……”, and discuss BiNM‟s
mathematical numerical analysis foundation, i.e. the spline and its mathematical polar characters.
So, we point out that the Hermite bicubic curved patch in numerical analysis equivalent to the
Eulerian operator in meteorology, and indicate that, as spectrum model, BiNM has her
mathematical convergence with the spline and the bicubic surface as well as their optimum
second-order derivative, and identify that the slope and curvature of centred finite difference are
justly three point smoothed ones of that of the spline. Using a global BiNM with latitude-longitude
grid, and holding the non-static and total compressible, adiabatic and non-frictional, and so called
“shallow atmosphere” equation set in the spherical coordinate, along with explicit semi-Lagrangian
time discrete integration scheme, and with adopting re-analysis data of NCEP for getting an initial
model atmosphere, we give a good simulation case. Lastly, we have to say that, because
atmospheric motion be essentially non-linear, the future BiNM could judge the reasonable local
area, or simple point to be smooth, according to the bicubic surface slope or curvature of one
variable field, which must conform to the physical interpretation, and if some instability area,
because of non-linear motion, be accordingly an origin place of some weather system, a global
multi-nested / time-variation grid BiNM must to be developed in future.
Key words: Bicubic Numerical Model (BiNM), spectrum model, finite difference model, numerical analysis, non-static and
total compressible dynamic core, explicit semi-Lagrangian time discrete integration scheme, simulation case
221
COMPREHENSIVE ANALYSIS ON SNOW EVENTS BASED ON
DOPPOLAR WEATHER RADAR IN NINGBO
HE Caifen, HUANG Xuanxuan
Ningbo Meteorological Bureau, Ningbo, China
ABSTRACT
Seven snow processes in Ningbo during the winter of year 2004 and 2007 are contrasted in
the paper. The comparative analysis makes use of conventional observational data, sounding and
Doppler Radar Data in many aspects such as weather background, temperature stratification,
characteristics of radar echo and so on. The conclusions of the paper are as follows: Continuous
low temperature, rainy and snowy weather in winter of 2007 is mainly caused by the great pressure
difference between west (high pressure) and east (low pressure) , the abnormally northward
movement of the subtropical high, the active southern system in Bengal bay and the La Niña
Events.Southwest current in middle and upper, the temperature inversion in the lower and middle
level , the northerly winds in the lower and the surface temperature that is below 4 ℃ are the
necessary conditions for snow. The strength and the influencing area of southwest current
determine the strength of the snowfall. Existing of the melting layer whose temperature is above
0 ℃ in the lower-middle level, and the surface temperature below 0 ℃ are the characteristic of
the freezing rain temperature stratification .The snow characteristic are that depth of freezing layer
should much thicker than the melting layer or there no melting layer , meanwhile the surface
temperature should be below 4 ℃ too. Generally speaking, the reflectivity of snow is less than
30dBz, the horizontal and vertical gradient of reflectivity is small and the structure is uniform. The
relationship between the reflectivity and the strength of snowfall is not clear. The spectrum width is
below 4m/s. The echo top is basically less than 6km. Do consider analyzing the change of the
height of the 0 ℃-layer bright band to nocasting the precipitation nature .The Radar radial velocity
data on analysis was found that the change of the zero velocity line is nearly same as the variation
trend of the sounding wind in the vertical. So the Radar radial velocity data can clearly state the
distribution of the cold and warm advection, and the wind speed in the strong wind area of the
Radar radial velocity data is nearly same as sounding wind speed at the same altitude. The analysis
of the distribution of the zero velocity line is of great significance to forecast the snow‟s end time.
Key words: snow; freezing rain; climate background; temperature stratification; Echo Characteristics; 0 ℃-layer bright
band
222
THE RELATIONSHIP BETWEEN GLOBAL ATMOSPHERIC
CIRCULATION AND THE ANNUAL FREQUENCY OF TROPICAL
CYCLONES AFFECTING GUANGXI
HE Hui, OU Yi
Guangxi Climate Center, Nanning, China
ABSTRACT
Based on the NCEP/NCAR reanalysis data, the interannual variability of the frequency of
tropical cyclones (TC) affecting Guangxi and the atmospheric circulation background during spring
and the TC season are studied using the correlation and composite analysis methods in this paper.
The results show that: 1)The annual TC frequency has a remarkable liner decreasing trend and a
prominent stage characteristic.2)From surface to 200hPa, the global atmospheric circulation
anomalies are remarkably correlated to the annual TC frequency , and the correlations have good
persistence from spring to the TC season. 3) The Antarctic Oscillation (AAO) and the geopotential
height anomalies over Australia are negative. The western pacific subtropical high is weaker, and
retreats east and north. The Indian-Myanmar trough is more intensify than climate average one.
These circulation conditions are beneficial to the convection over Intertropical Convergence Zone
(ITCZ) near South China Sea. As a result, the frequency of TC affecting Guangxi is greater than
normal.
223
ANALYSIS ON SUPER HEAVY RAIN CAUSED BY THE
SUPER-TYPHOON ―SEPAT‖
HUANG Xiaoyu 1, 2, CHEN Yuan1, CAI Ronghui1
1
Key Laboratory of Hunan Province for Meteorological Disaster Prevention and Mitigation
2
Hunan Meteorological Office, Changsha, China
ABSTRACT
During 19～24 August 2007, sustained extremely heavy rain occurred in southeast Hunan
Province caused by the Super-TY “Sepat”. Using the conventional meteorological data, numerical
forecast products, satellite cloud image and Doppler radar data, the features of the case were
analyzed. Results show that, the case occurred because of that Typhoon trough combine with
southwest monsoon. it Strengthened the dynamic dondition of precipitation and was favorable for
the vapor flowing to China. The characteristic of mesoscale-βconvection system was analyzed in
cloud image. the echoes experienced the stages of initial genesis, helix band, merging, decreasing
and extinction. The movement changed from intruding northeastly, rotating around the radar,
moving out northeastly. The train effect is the major character of this event. Even though the averse
wind regions in the image of velocity, the well organized secondary circulation caused by
discontinuous meso-scale jet-core at the medium level of troposphere maybe the main reason to
form and sustain the train effect. At the low level, the spectral width is quite high and within the band
of severe echoes there is another extreme high center at high level, and at the medium level it is
very homogeneous. This indicates that the turbulence caused by surface friction is very strong and
the stable jet at medium level is the major reason of the long duration of the event.
Keywords: Super-Typhoon “Sepat”, super heavy rain
224
ANALYSIS OF ICE AND SNOW FALL DISASTER WEATHER
FROM TEMPERATURE DATA IN DA BIE MOUNTAIN AREA
MA Jianguo, JIANG Bing, LI Qiang
Lu’an Meteorological Bureau, Anhui, China
ABSTRACT
2008 has been the longest year of continuous snow falling in Da Bie Mountain area since
1949.(21days) The maximal snow cover depth area concentrates Anhui Province in Da Bie
Mountain area , is also that the deepest area of the whole nation snow cover depth , the maximal
snow cover depth is 54 cm of Da Bie Mountain area Jin Zhai County. Snow cover and frost for a
long time bring about bad effect to traffic, electric power, and day of people‟s life, especially the low
temperature, snow cover brings about the road surface icing, that is one kind of unobstructed bad
weather of serious harm floor disaster, the strong road surface freezes to cause the traffic of
mountain area to be interrupted reaching 20 days. The article analyzes the average temperature in
January over the years in Da Bie Mountain area.
By analyzing freezing and snow falling from 1971 to 2000 in Da Bie Mountain area in
January, it have discussed the law of the time change about snow cover and freezing , it also have
summed up the key factor of freezing and snow fall; At the same time by analyzing the cause of
sustained low temperature of area , ice and snow from temperature condition in Da Bie mountain
area in January, 2008, it can be seen: Stable, advantageous atmosphere circumfluence
circumstances, has provided condition to sustain low temperature snow falls and freezing. The
advantageous vertical temperature distribution is the direct cause of strong freezing. snow cover
and the low temperature forming the floor bring about the floor freezing a disaster; By analyzing
comparing with history value of forecast , and combining with the weather characteristic value of low
temperature , snow falls and frost, having built the forecast serves technological process of the
snow fall and road surface frost.
Key word：snow and ice disaster；temperature condition；forecast procedure
225
THE ROLE OF WINTER EURASIAN ATMOSPHERIC COLD
SOURCE IN SNOW STORMS OF SOUTH CHINA
Sulan NAN, Ping ZHAO
Chinese Academy of Meteorological Sciences, Beijing, China
ABSTRACT
Using station observations of the number of snowfall days (SFD) in China, and the National
Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR)
reanalysis for the period of 1953-2008, temporal variations of January SFD in South China and the
Eurasian Atmospheric Cold Source (EACS), and the relationship between them are investigated
statistically.
There is significantly positive correlation between the January EACS and SFD in South
China. The large-scale atmospheric circulation anomalies over the Eurasian continent are also
related to the EACS. When the EACS is high, an anomalous anticyclone appears over the East
European Plain and West Siberian Plain, which is favor of the forming and holding of blocking,
helpful for the persistent cold air into China; and an anomalous cyclone appears in South Asia and
East Asia, leading to the warm and wet air currents into China from South Asia, Bay of Bengal and
South China Sea. During the high EACS phases, the upward (downward) motions enhance (reduce)
in South China; the water vapor flux convergence (divergence) enhances (reduces). These
situations provide necessary circulation and water vapor conditions for the increase of snowfall in
South China; and vice versa. These anomalous atmospheric circulations also occur in January
2008 and lead to the infrequent snow storm disaster. The EACS in January 2008 is much higher
relative to the climatology and is the most outstanding in the recent 30 years, coinciding with snow
storms in South China. The EACS may be an indicator of January snow storms in South China.
226
ANALYSIS OF HUAI'AN CITY SNOWSTORM AND
LOW TEMPERATURE WEATHER
ON JANUARY 18TH TO 20TH IN 2008
QIN Chengyun, CHEN Hui, LIU Hongbin
Huai'an Meteorological Bureau, Huai'an, China
ABSTRACT
Huai'an City appeared snowstorm on January 18 to 20 in 2008.the article has used
conventional ground, high-altitude observation material and numerical prediction products, evolved
from the atmospheric circulation evolution of the situation, as well as the northern cold air activity
and the southern warm and humid air streams transportation and so on, promulgated this storm
synoptic process origin. The analysis had discovered: Before this storm weather occurs, the
southwest jet stream of 700 hPa and 500hPa has provided the sufficient water vapor condition for
the storm production. The warming - Shear line of 700hPa and 850hPa、the high-level divergence
and low-level convergence produced for the storm has provided the sufficient dynamic condition.
The northern cold air went south has uplift southwest warm and humid air streams, is trigger
mechanism which the storm produced, simultaneously has guaranted the temperature conditions
which the storm formed needs. ECMWF and Japan numerical forecasting's precipitation magnitude,
the precipitation region have the good reference function to the predictor.
Key words: Storm, weather system analysis, numerical forecasting product.
227
ANALYSIS ON INFLUENCE FACTORS OF THE ABNORMAL
LOW TEMPERATURE, SLEET AND FROST WEATHER IN
GUANGXI PROVINCE AT THE BEGINNING OF 2008
QIN Zhinian1, ZHONG Lihua2, LIU Lihong3, ZENG Peng2, FU He4
1
Guangxi Climatic Center, Nanning Guangxi, China
Guangxi Meteorological Science and Technology Service Center; Nanning Guangxi, China
3
Training Center of China Meteorological Administration, Beijing, China
4
Guangxi Research Institute of Meteorological Disasters Mitigation; Nanning Guangxi, China
2
ABSTRACT
During Jan.12 to Feb.20 of 2008, the low temperature, sleet and frost weather process
occurred in Guangxi, which duration is the longest and average temperature is the lowest since
1951, the cumulative temperature of process reached the standard of abnormal low. Circulation
features and indices of six remarkable low temperature and sleet processes at the corresponding
period in Guangxi were analyzed, then EMD research were carried out for two kinds of circulation
indices which have the obvious coherence, results showed that major circulation characteristics of
abnormal low temperature of Guangxi were dipole type of 500hPa circulation in the northern
hemisphere, the lower geopotential height in the western of China, the abnormal active trough and
stable high over Siberian or Mongolia. The active southern branch trough, stronger frontal zone in
Guangxi and trough in Mongolia were the necessary conditions for abnormal low temperature
synoptic. Frontal zone of Guangxi had been on the ascending phase of 8-year period and the
southern branch trough had been on the intense phase of 7-year period in 2008, both 2-year period
and 17-year period of the low temperature variation of Guangxi had been enhanced at the same
time, so that the low temperature, sleet and frost synoptic process happened in Guangxi province at
the beginning of 2008.
Key words: Guangxi; abnormal; low temperature; sleet; frost; influence factors
228
ANALYSIS OF JIANGSU SNOWSTORMS CLIMATE
CHARACTERISTICS
TAO Mei, XIANG Ying, XU Xiazhen, WANG Kefa, XIAO Hui
Jiangsu Climatic Center, Nanjing, China
ABSTRACT
This article analyzes decade variations, space distribution rules and climate characteristics
statistics of blizzards according to the observation data of snowstorms in Jiangsu form 1951 to 2008.
Analyze middle and high latitude circumfluence and tropical convective activities happened during
blizzards in 2008. Discuss the effect on blizzards by La Nina event. Compare with historical
snowstorms. Analysis showed that blizzards in Jiangsu mostly occur form November to March the
following year, most in February. There was no blizzard in 9 years from 1961 to 2008. And there
were 5 years without snowstorm in the sixties. The maximum number of dates of blizzard is 90 in
2008. There may be area blizzards in strong La Nina year, not always in weak La Nina year
however. Historical comparative analysis showed that, in the months of blizzards, index of Asian
zonal circulation is low, west wind circumfluence reduces, winter monsoon is strong, both West
Pacific subtropical high and north border of West Pacific subtropical high are strong and move
towards north and The India-Burma trough is deep.
Key words: blizzard La Nina Subtropical high over the west Pacific
229
EFFECTS OF THE TIBETAN PLATEAU AND THE MOUTAINS
OVER SOUTHEASTERN CHINA ON THE FORMATION
OF THE PLUM RAINS
WAN Ri-jin, ZHAO Bing-ke, YING Ming
Shanghai Typhoon Institute of the China Meteorological Administration, Shanghai, China
ABSTRACT
The Plum Rains (PR) to the south of the middle and lower reaches of Yangtze River over
southeastern China (SEC) is one of the important components of the East Asia Subtropical
Monsoon system. It is the result of the process of the marching northword of warm and wet
southwesterly with season warming. Climate mean data analyses and numerial model sensitivity
experiments are used to study the formation of PR. Data analyses shows, at lower troposphere,
SEC is located at the downstream of a southwesterly velocity center and there is mechanically
forced rise of the southwesterly flow by the moutains over SEC. As a result, there is strong
southwesterly velocity convergence and moisture convergence over SEC. That is the immediate
climatic cause of PR formation. Sensitivity numerical experiments shows, without the Tibetan
Plateau (TP), the southwesterly jet over SEC become stronger, its voticity increases, and PR
increases by 2 mm/d. In other words, with TP standing, its Sensible Heat Air Pump (SHAP) makes
the circulation‟s voticity increasing over its surrounding areas but decreasing over SEC by
dispersing Rossby waves and thus makes PR decrease. On the other hand, without the moutains
over SEC, the PR decreases by 2 mm/d and the rain belt shifts north to the Huaihe rivers reaches.
On the contrary, with the moutains lifting by 300 m, PR increases and the rain belt shifts south.
These indicating that the moutains over SEC can force the southwesterly rising and magnify PR. So
the moutains over SEC also has important effect on the formation of PR. Thus it can be seen, PR is
originally produced by the typical East Asia Summer Monsoon, which is caused by see-land thermal
contrast. PR is also affected heavily by the nearby huge plateau and moutains through their thermal
and mechanical forcing. These can help us to understand the origin of the summer monsoon and its
rains over East China.
Keywords: the Plum Rains, southwesterly jet, the Tibetan Plateau, the mountains over southeastern China, sensitivity
numerical model experiments.
230
THE DISTRIBUTION OF RAINFALL ASSOCIATED WITH EAST
ASIA MONSOON IN MEIYU SEASON
WANG Hui, YAO Jianqun, SHI Chunhong
Shanghai Weather Forecast Center, Shanghai, China
ABSTRACT
In the middle of last century, a significant achievement was made by Chinese
Meteorologists; a distinguished circulation over East Asia in summer was found which was different
from its counterpart over South Asia, the Indian monsoon circulation. Some further researching
improvements revealed the specific members of such East Asian monsoon circulation in 1980s; one
of them is Meiyu front which plays an important role in East Asia summer raining season. Soon later,
Chinese scientists discovered more facts about East Asian monsoon. Because the eastern Asia
continent surrounded by Indian Ocean to south and by Pacific Ocean to east and southeast, thus,
the difference of temperature between land and ocean can produce a vast relative lower pressure
over eastern Asian, which induces a vast cyclonic circulation at low level in far eastern Asian,
driving tropical currents flowing towards further north area; at the same time, the subtropical system,
such as the subtropical high, partly influenced by the temperature difference between Euro-Asian
continent and Pacific Ocean, can also lead the currents on its western periphery to a higher latitude.
So it is reasonable to think that the East Asian Summer Monsoon involves tropical and subtropical
parts in it. Chinese scientists used to describe them in names of tropical monsoon and subtropical
monsoon.
Therefore, the rainfall in East Asia and China is not only affected by one of these two
summer monsoons. This can be easily proved by confused statistic results of the rainfall over China
depending on only one element, tropical monsoon or subtropical monsoon. The rain pattern in East
Asia and China should be dominated by both behaviors of tropical and subtropical monsoon which
varies in a year. In order to get a relative clear image of rainfall distribution in China, an analysis
was performed to research the relationship between the most possibility of a rainfall pattern and the
different strength of tropical and subtropical monsoon, using the continuous records series of
tropical monsoon (South China Sea monsoon, hereafter SCSM) indices, subtropical monsoon
(hereafter STM) indices, and rainfalls over eastern China in more than 50 years. Based on the value
of two monsoon indices, all monsoon years were categorized into 9 types: abnormal strong SCSM
and abnormal strong STM years, abnormal strong SCSM and normal STM years, abnormal Strong
SCSM and abnormal weak STM years, normal SCSM and abnormal strong STM years …, etc.
accordingly 9 types of rainfall pattern over China were displayed.
Key words: Rainfall pattern; Meiyu season; Tropical monsoon; Subtropical monsoon
231
ON ZONAL SHIFT OF SUBTROPICAL HIGH IN CONSERVATIVE
ABSOLUTE VORTICITY CONTEXT
WanLi WANG1, 2, ZuWu WANG1
1
School of Resource and Environmental Science of Wuhan University, Wuhan, China
2
Wuhan Regional Climate Center, Wuhan, China
ABSTRACT
Via some exploration Subtropical High (SH) zonal shift may be controlled by a group of
basic equations including the Vorticity Equation; Geostrophic Equilibrium Equation; Thermal-wind
Equation; Static Equilibrium Equation and Equation of State depending on vital postulate that mean
zonal wind and absolute vorticity are both constant in atmosphere, Then the end outcome is
formula deduced as bellow
  0 
(TL  TH ) TE  TW
R2
(
)
2
x
2 Re cos  ( H   L )
  0 
vH  vL
Re cos 
Or
Here  is longitudinal value of the position of SH ridge point , unit is radian,  is a given
latitude value ,  0 is initial longitudinal value of the position of SH ridge point , Re2 is earth
angular momentum at equator, R is well known as gas constant, TL is temperature at low
pressure level , And TH is temperature at high pressure level. TE and TW is respectively
temperature at east side and west side . in addition   gz which is value of geopotential height
of pressure level, ( H   L ) denotes mean geopotential height between two pressure level,
(TE  TW x) is zonal temperature gradient meanwhile x is a distance of east to west or west to
east in unit of meter, (v H  v L ) indicates perpendicular shear of meridian wind. Main results (1) if
zonal temperature gradient is positive and becomes increasing then the point of Subtropical High
ridge will be withdrawn from west to east and vice verse. (2) Similarly the point of subtropical high
ridge will jump to east from west once shear of meridian wind is positive and changes into great, as
well as also vice verse. (3) Nearly at the ridge point, there is a zonal thermal circulation which
resembles Walker circulation with respect to thermal feature. (4) Finally the formula also involves
quasi indices of South Oscillation when Equation of State is considered. Perhaps this physical
model can advance our understanding about some new properties of SH when it moves in zonal
direction.
Key words: Subtropical High, east or west movement, meridian wind vertical shear, zonal temperature gradient, zonal
thermal circulation
Note: zonal is referred to in west-east or east-west direction and meridian means in north-south or south-north direction in
this paper.
232
MESOSCALE ANALYSIS OF A HEAVY RAIN EVENT
DURING MEIYU PERIOD IN 2007
WANG Xiaofang
Institute of Heavy Rain, Chinese Meteorological Administration, Wuhan 430074
E-mail:[email protected]
ABSTRACT
A rear-fed leading stratiform mesoscale convective system（RFLS MCS）was observed in
middle part of Hubei province during Meiyu Period of 2007. The stream structure and dynamical
feature of the RFLS in Jun 18th, 2007 are analyzed by LAPS developed by ESRL(Earth System
Research Laboratory), USA, using NCEP1°  1°daily reanalysis data, operational observation data
and radar data. The horizontal reflectivity structure observed by radar is as follows: convective cells
sometimes elongated and canted with respect to the convective line, a transition zone of lower
reflectivity, and an area of enhanced stratiform rain. The 18 June system has an overturning updraft
during its early stages, and produce leading stratiform precipitation. In mature stages the vertical
flow develops strongly, and the frontal stratiform echoes continue to strengthen. The
line-perpendicular vertical wind shear in low-middle troposphere layer increasing over time and the
surface cold pool weakening or keeping changeless over time are the main causes for which this
RFLS system updraft flow tilts frontward. The 18 June RFLS system mainly consists of three flow
branches: rear-to-front inflow, front-to-rear descending inflow and ascending flow which produce
stratiform cloud anvil by tilting the rear-to-front flow in the middle-upper troposphere layer. Front
uplifting action in convective area and strengthening ascending movement with the increasing wind
vertical shear are possible reasons of development of instability in convective area.
233
SITUATION ANALYSIS AND FORECAST OF THE
PRECIPITATION IN THE HUAI RIVER VALLEY DURING 2007
RAINY SEASON
WANG Yonghong, SONG Haiou, YU Jihua, Fei Hongwei, Bo Lianhong
HuaiAn Bureau of Meteorology, HuaiAn, China
E-mail: [email protected]
ABSTRACT
Regional continued rainy season precipitation occurred mainly in the process of subtropical
anticyclone‟s carrying into the North West, the northern edge of which provide full warm and wet air
currents to intersect with the cold air from the low pressure of Mongolia which is moving toward
south continually, all of which result in the shear line convergence zone between the Northwest and
the southwest airflow from the Yellow River to the Yangtze River, and finally, a sustained and
steady rain bands has been formed. The existence of the low-shear line and ground low pressure
promote and strengthen the development of the troposphere. In the Huai River Valley regional
precipitation in 2007, the low-shear line has played a vital role, which is present in almost all of the
strong precipitation, and coupled with frequent surface low-pressure system activities that promoted
the occurrence and development of the strong convection. In this paper, we will take an example of
the regional continued rainy reason precipitation in Huai River in July 2007 and analyze the
circulation system characteristics of the continued precipitation. The use of a number of numerical
prediction products will get the better effect in its short-medium-term forecasting.
Key words: continuity of the precipitation circulation features numerical prediction products forecasting service.
234
CHARACTERISTICS OF 500HPA CIRCULATIONS OF
CONSECUTIVE RAINSTORM EVENT IN PRERAINY SEASON IN
GUANGDONG IN 2008
Wen Jing1, Ji Zhongping1, 2, Xie Jiong’guang1
1 Guangdong Meteorological observatory, Guangzhou, China
2 The state key laboratory of severe weather, Chinese Academy of Meteorological Sciences, CMA, China
ABSTRACT
Guangdong had been suffered form the heaviest rainfall process in the late May to 18th June,
2008 since 1951. Based on the analysis of the large-scale 500hPa pentad average circulations of
the start, endurance and end of this process, the results show that, the endurance of the
two-trough-and-two-ridge or two-trough-and-one-ridge circulations in high latitude of Eurasian
continent supplies weak cold air for the heavy rainfall process, the trough over the Bay of Bengal
transfers sufficient vapor, and the intensification and westward stretch of the western Pacific
subtropical high strengthens the warm and moist stream to trigger the torrential rain event.
Key words: synoptic； blocking high； East Asia major trough； warm and moist stream； consecutive rainstorm；
Guangdong
235
VARIATION FEATURES OF SOUTH CHINA SEA (SCS)
CROSS-EQUATORIAL FLOW AND ITS RELATION TO
PRECIPITATION IN FUJIAN PROVINCE
XU Jinjing, CHI Yanzhen, WEN Zhenzhi, HE Fen
Fujian Climate Center, Fuzhou, China
ABSTRACT
Herein the variation features of South China Sea (SCS) cross-equatorial flow and its relation
to precipitation in Fujian Province are studied. It is turned out that: 1) the SCS cross-equatorial flow
has a tendency of increasing in winter and decreasing in summer in the near 44a; 2) in summer half
year, the intensity of SCS cross-equatorial flow has a better lag positive correlation and has a
obvious persistence from April to September; 3) there is a significant positive correlation between
cross-equatorial flow and Fujian precipitation in spring and former autumn and winter, The variation
of intensity and its persistence may provide reference for the short-term climate prediction of spring
precipitation in Fujian Province
Keywords: SCS cross-equatorial flow ; precipitation ; correlation analysis.
236
EXPERIMENTAL PREDICTION OF WESTERN NORTH PACIFIC
TROPICAL CYCLONE NUMBER
XU Ming, YING Ming, YANG Qiuzhen
Shanghai Typhoon Institute, China
ABSTRACT
A statistical model for the prediction of tropical cyclone (TC) activity has been developed
and applied to the western North Pacific. It aims to predict the number of tropical cyclones over a
certain period. The model is based upon regression analysis. The predictors for the regression
model are obtained by examining the lag correlations between the predictand and the synoptic
variables such as 500hPa height, sea level pressure, 200hPa wind speed, SST. The predictions
were carried out before TC season during 2005-2008, and the results of the prediction were
analyzed.
237
SOUTH CHINA SEA SUMMER MONSOON ONSET TIME AND
DROUGHT/FLOOD DISASTER DISTRIBUTION OVER
EAST ASIA REGION DURING SUMMER
YANG LIN1, 3, WEI Ying-ZHI 2, DING Yi-hui3, PAN Ning4
1
Fujian Climate Center, Fuzhou 350001, China
Fujian Meteorological Bureau, Fuzhou 350001, China;
4
3 National Climate Center, Beijing 100081, China; Fujian Meteorological Observatory, Fuzhou, China
E-mail: [email protected]
2
ABSTRACT
The drought/flood disaster often take place in East Asia region as a result of summer
monsoon transformation event years, South China Sea summer monsoon onset time and
corresponding atmosphere circumfluence state is an possibility importance forecast signal by
scientific research, this paper define disaster degree of drought/flood by summer precipitation
percentage, the relation between three typical South China Sea summer monsoon onset
time(earlier, later and normal) event years and the distribution of drought/flood disaster in East Asia
region is researched by compound diagnosis methods, using the data of the historical surface
precipitation observed at 529 stations in East Asia region, the conclusions is scientific signification
and application value. The preliminary results were as follows: (1) In the years when summer
monsoon over South China Sea onset early(figure 1 and figure 4), Yang-Zi river valley, the north
part of North-east China, some parts of Hua-bei Plain, the south part of South Korea, the south part
of Japan and the east of Mongolia, the summer rainfall was partial little, that easy emergence is
drought ; the east part of Hua-Nan region, Huai-He river valley, the north of Bo-Hai gulf, the
boundary of both China and Korea and the north of South Korea , summer rainfall was partial more ,
the easy emergence was flood. (2) In the years when the monsoon onset late(figure 2 and figure 5),
the south of Yang-Zi river, South-east cost, Hainan island, parts of North-east of China and the east
of Japan, was partial little, that easy emergence is drought ; the west of Hua-Nan area, Huai-He
river basin, most parts of Hua-Bei area, the east part of Nouth-East of China, the south of South
Korea and south of Japan, summer rainfall was partial more , the easy emergence was flood. (3) In
the years when the monsoon onset in normal time(figure 3 and figure 6), the south part of Hua-Nan
area, Yang-zi & Huai-He river valley, the boundary of both China and Korea, the boundary of both
China and Mongolia, some parts of South Korea and the south of Japan, the summer rainfall was
partial little, that easy emergence is drought ; But in the same condition, the west part of Jiang-Xi
province and most parts of Japan, summer rainfall was partial more , the easy emergence was
flood.
Acknowledgement: This research was funded by Natural Science Foundation of Fujian Province in 2004 under Grant
No.D0410026.
Keywords: South China Sea summer monsoon, onset time, East Asia region, drought/ flood disaster, distributing pattern
figure 1
figure 2
figure 3
figure 4
figure 5
figure 6
238
GLOBAL CLIMATE CHANGE AND EVOLVEMENT OF
THE SOUTH CHINA SEA SUMMER MONSOON (SCSSM)
ONSET TIME
YANG Lin1, 3, WEI Ying-zhi2, DING Yi-hui3, ZHANG Xiu-zhi3
1
2
3
Fujian Climate Center, Fuzhou, China; Fujian Meteorological Bureau, Fuzhou,China; National Climate
Center, Beijing,China
E-mail: [email protected]
ABSTRACT
The South China Sea summer monsoon (SCSSM) onset is not only considered as auspice
signal to the East Asian summer monsoon onset, but also a significant turning point or switch during
the abrupt transition of climate season in the Asian region. In this paper, the adaptation and
evolvement of SCSSM onset time was carried through relatively research in the background of
Global climate change, based on the data of the historical serial of SCSSM onset times offered by
Beijing Climate Center(BCC), we study and analyze its climatological characters of adaptation and
evolvement in multiple time-scale during near 55a (Fig.1 ).The preliminary results were as follows:
SCSSM onset time take place different adaptation and evolvement every years in the near 55a
under the impact of Global climate change, in the near half century (from 1951 to 2005), the
standard deviation of annual change rate of SCSSM is 1.73 pentads. Mean range of variation is 8 to
9 days. The earliest onset time is 25 pentads, the latest is 32 pentads, its variety extent is 7 pentads,
that is approximately 30-35 days. The mean onset time of SCSSM in near 55a is 28.78 pentads.
The changing adaptation process can be generally divided into two periods, in the first period which
lasted for 43 years from 1951 to 1993, the onset time fluctuated repeatedly between earlier and
later, the second period is from 1994 up to now when the onset time were obvious early. The
SCSSM onset time obviously early (less than 28 pentads) appeared 10 times, they are 1951, 1966,
1994, 1972, 1996, 1979, 1986, 1995, 2000 and 2001. The SCSSM onset time obviously late (more
than 30 pentads) appeared 9 times, they are 1970, 1973, 1987, 1991, 1954, 1956, 1971, 1981 and
1982. The SCSSM onset time basically normal (between 28 and 30 pentads) appeared 36 times
(including those years which the deflection is slim). The exact normal event years (equal to 29
pentads) appeared 14 times, they are 1952, 1953, 1955, 1958, 1962, 1965, 1967, 1969, 1974, 1978,
1983, 1984, 1988 and 1999. In the adaptation and evolvement process of SCSSM onset time,
basically normal event years dominate which take up 66%, obviously early event years take up 18%,
and obviously late event years take up close to 16%, after 1993, obviously early event years
manifold visibly.
Acknowledgement: This research was funded by Natural Science Founation of Fujian Province in 2004 under Grant
No.D0410026.
Keywords: Global climate change, South China Sea Summer Monsoon, onset index, adaptation and evolvement,
multiple time-scale
Fig.1 The frequency chart of small-wave of SCSSM onset time near 55a
239
THE RELATIONSHIP BETWEEN ENSO AND WINTER AVERAGE
TEMPERATURE OVER HONGZE LAKE
YANG Qingping1, ZHENG Yang2, FEI Hongwi3
1
Huaian Meteorological Bureau, Jiangsu, China
Jiangsu Institute of Economic & Trades Technology, China
2
ABSTRACT
This thesis analyses the average temperature in winter which covers the Hongze Lake. It is
concluded that the average temperature of the Hongze Lake increased 2℃ in the winters of the
past 47 years; the average temperature keeps above 2℃ in 1986-2006; The average winter
temperature is remarkably higher in 2006; in 2007, the average temperature of February is the
highest in the history, it is a year that the temperature is higher unconventionality; comparing with
the normal years, the middling ENSO has smaller influence on the average winter temperature of
the Hongze Lake area; After a weak ENSO , the average winter temperature in Hongze Lake area
will have a low trend, and the average temperature in February of the following year will drop more
than 1.5 ℃ in contrast with the average temperature in February of the last.
Key words：the Hongze Lake area, the average temperature in winter, being remarkably higher, ENSO
240
A NUMERICAL STUDY ON THE CHARACTERISTICS OF THE
WATER VAPOR TRANSPORT OF TROPICAL CYCLOON
INTERACTING WITH THE SOUTH CHINA SEA MONSOON
YE Chengzhi1, 2, 3, LI Yunying4
1. Institute of Heavy Rain, CMA, Wuhan 430074; 2 Hunan Meteorological Burean, Changsha, China
3. State Key Laboratory of Sever Weather, Chinese Academy of Meteorological Sciences, Beijing, China
4. Institute of Meteorology, PLA University of Science and Technology, Nanjing, China
ABSTRACT
After landing of the tropical storm of Bilis (200604), the low-pressure circulation resided in
the Chinese east coast areas for a quite long time, interacted with the south China sea monsoon,
and led to a recorded rainfall in the southeast part of Hunan province. In this study, based on the
multiple general observations, non-general fine grid‟s observations and the NCEP reanalysis data,
as well as the simulation and diagnosis data of meso-scale numeric model of AREM on this process,
a sensitive experiment had been designed in order to reveal the specific water vapor source and the
flowing channel in the Hunan southeast heavy rain process. The results show that the south China
sea monsoon acted as a key role in the water transportation in this heavy rain process, by the
Anti-clockwise rotating of the storm Bilis, the vapor accessed to the north of the low circulation
along with the strong wind of east side of the storm center. Afterwards, the increased northeasterly
brought the water vapor to the southeast of Hunan continuously.These two strong moisture current
intercrossed in the southeast of Hunan and formed a deeply wet layer and strong vapor
convergence here also the heavy rain area, and it was very contributed to the Bilis maintenance for
a long time to contribute the heavy rainfall. The vapors of condensed rainfall mainly came form the
convergence of lower layers‟ wind, making the low vapor up transported to the middle and high
levels through local air vertical convection. Inadition, the special terrain, interreacted with increasing
northeasterly current, also had a positive contribution to the intensity of this rainfall process.
Key words: the tropical storm of “Bilis”, heavy rain, the numerical simulation.
241
STUDY ON THE CHARACTERISTICS AND ITS CAUSE OF A
RARELY-SEEN LOW TEMPERATURE, FREEZING RAIN AND
SNOWFALL WEATHER EVENT OVER SOUTH CHINA
YE Chengzhi1, WU Xianyun2, WANG Qi3
1
Hunan Meteorological observatory, Changsha, China
2
Hunan Climate Center, Changsha, China
3
Hunan Meteorological Serve Center, Changsha, China
ABSTRACT
In the background of the Ural blocking high circulation sustaining in mid-high latitude over
Eurasia, four consecutive large scale disaster weathers of low temperature, freezing rain and
snowfall covered southern China during the period of Jan. 10 to Feb. 2, 2008. Using the multiple
conventional and non-conventional observations, and the NCEP reanalysis data, through studying
the whole freezing weather processes and the distribution of freezing rain, the features of
atmospheric circulation and water vapor transportation are diagnosed, and the causes of producing
different types of precipitation are investigated. The results show that, the atmospheric circulation
anomaly over Eurasia, the Ural blocking high , the East Asia trough, the west Pacific subtropical
high, the Indian and Burma trough and their abnormal arrangement provided large scale circulation
background for this disaster weathers of low temperature, freezing rain and snow; sustaining and
abundant water vapor transportation had a important influence on the intensity and scale of this
weather process, but the contributions of all water vapor sources were different in four weather
processes. In the first two, water vapor was mainly transported from the Qinghai-Tibet Plateau and
southeastern flow from the west Pacific subtropical high, the former had obvious influence on the
downstream precipitation. For the following two, water vapor was transported by the southwestern
flow from northeastern Bengal bay to northern the Indo-China Peninsula and southeastern flow
from northern South China Sea, the stronger vapor transportation was likely the main reason
leading freezing rain more lager area and higher intensity. Furthermore, the existing of colder water
drops in near ground and the establishing of warm-type inverse temperature above the thick cold
layers possibly are the key factor to maintain the bad weather process. Under the precipitation
condition, the increases of temperature and humidity near 700hPa, strong decrease of temperature
below 850hPa and that the mean temperature on the ground is lower than 0℃ provided the
significant indications for the freezing weather forecasting.
Key words: low temperature freezing rain and snowfall, the characteristics of evolvement, the cause of freezing rain
formation
242
ANALYSIS ON THE CAUSE FOR ABNORMAL
WATER-LOGGING IN FLOOD SEASON 2005 IN SANMING
ZHANG Dahua, SHEN Yongsheng, CHEN Yandie,
HAN Xiurong, WANG Zhengting
Sanming meteorological Bureau of Fujian Province, Sanming, China
ABSTRACT
Based on the statistical analysis for precipitation data in flood season (May and June) from
1961 to 2005 in Sanming, the tome and locality distribution characters and periodic variation
regulation of the water-logging years in flood season are revealed. The circulation characters of
abnormal water-logging in flood season 2005 are analyzed and compared with the ordinary year
average, using 500hPa monthly mean height field, the results as follows：
1．Month precipitation exceptionally much happened in 11 years and at 45 stations in May
and at one-year-average rate of 24.4% and in 14 years at 55 stations in June at one-year-average
rate of 31.1% from 1961 to 2005 in Sanming. Exceptionally water-logging and abnormal
water-logging in flood season happened at 4 years (in 1962, 1977, 1994 and 2005) with a rate of
one-year-average at 8.9%, among of them, abnormal water-logging in flood season happened at
one year (in 2005) with a rate of one-year-average at 2.2%。
2．Phenomenon of month precipitation exceptionally much occurred in May in history, the
phenomenon occurred most currently at middle-west stations of Sanming urban, Ninghua, Jiangle
and south station of Datian at a one-year-average rate of 11.1%. The same phenomenon happened
in June, mostly at west station of Qingliu in 7 years at a one-year-average rate of 15.5%, secondly
at middle-west stations of Sanming urban, Ninghua, Mingxi in 6 years at a one-year-average rate of
13.3%。
3．It was he main cause of abnormal water-logging in flood season 2005 that the east Asia
trough was obviously to the east, subtropical high area was larger and intensity was stronger than
average, but ridge line was obviously to the south。
4．Because of the position prediction of subtropical high ridge was moderate and stable in
May anb June. flood season of Sanming started early, ended late and lasted long. This was one
reason of abnormal water-logging of flood season in 2005.
243
ANALYSIS ON LARGE-SCALE CIRCULATION
CHARACTERISTICS OF MEIYU RAINSTORM AND THE
STRUCTURE OF MEIYU FRONT IN ZHEJIANG PROVINCE
DURING 2008
ZHANG Jian-Hai1, SHEN Jin-Dong2
1
Shaoxing Meteorological bureau, Shaoxing, China
2
Lanxi Meteorological bureau, Lanxi, China
ABSTRACT
Using the objective analysis and observation rainfall data, the large-scale circulation
characteristics and the structure of meiyu front of the two intense rainfall in zhejiang province during
2008 are contrast analyzed. The result are follows:（1）The 2008 is very typical Meiyu year since
1999, the total precipitation is 20% more than that in average years and has 5 systematic intense
rainfall processes in all during Meiyu period. （2）On the high level, Northly flow which locate in
northeastward of the stable and strong southern Asia high provide intense divergence field for
rainstorm region. The lower South-westly jet transports moisture which come from the Bay of
Bengal and South China Sea to rainstorm regin and constitutes a zonal shear line with eastly flow
which locate in northward of zhejiang, The maintaining of upper and lower jet and much warm-wet
moisture convergence provide favorable lifting mechanism and water vapour condition. （3）On the
middle level, Circulation situation at 500hPa has a sudden shift from single-blocking high type to
double-blocking high type which lead to long-time rainy day. Intense rainfall region corresponding to
Meiyu front is relatively low on temperature field and there is no gradient, on the other hand the
gradient of equivalent temperature and moisture is very obvious. （4）Contrast analysis of the
structure of Meiyu front between two intense rainstorm indicates that the distribution of first
rainstorm is near to west-east and the main rainfall stand on the front of Meiyu front, but the third
rainstorm has a Meridional distribution and the main rainfall locate in the middle of Meiyu front. On
the structure of thermal-wet, the gradient of temperature of the first rainstorm is greatly than that of
the third one.At the same time, the positive of vorticity and divergence of the first rainstorm on the
middle-low level of troposphere is more deeply than the third rainstorm.
Key words: Meiyu front, Rainstrom, Circulation Characteristic, Contrast analysis
244
CHARACTERISTIC OF LOW LEVEL EAST ASIAN WINTER
MONSOON AND THEIR IMPACT ON ANOMALOUS JANUARY
TEMPERATURE OVER CENTRAL CHINA
ZHANG Liping
Wuhan Regional Climate Center, Wuhan, China
ABSTRACT
Low level East Asian winter monsoon characteristic of samples long sleet over Hubei
Province in winter were analyzed with NECP/NCAR reanalysis of 850hPa wind. January 2008 the
anomalous displays in that as the Mongolian high pressure is strong, and Aleutian low pressure is
strong and westward, geostrophic wind or north wind over border of East Asian continents between
high and low pressure is strong, otherwise south wind is strong over the middle and lower reaches
of the Yangtze River and the south. A common of samples long sleet over Hubei Province in
January or February is that south wind is strong obviously over the middle and lower reaches of the
Yangtze River or the south, and there were large size of anomalous of anticyclone or cyclone over
the north of Pacific. By SVD between November 850hPa wind and next January temperature over
the Middle of China the results were indicated that when November on 850hPa anomalous of
cyclone over Aleutian is strong first, there were anomalous of cyclone over East of Island of Taiwan
or there were anomalous of anticyclone over the east second, following next January temperature
will be lower over the Middle of China, contrariwise.
245
RELATIONSHIP BETWEEN THE ASIAN-PACIFIC OSCILLATION
AND THE TROPICAL CYCLONE FREQUENCY
IN THE WESTERN NORTH PACIFIC
ZHOU BoTao1, CUI Xuan2, ZHAO Ping3
1
Lab. for Climate Studies, National Climate Center, China Meteorological Administration, Beijing,, China
2
National Meteorological Center, China Meteorological Administration, Beijing, China;
3
Chinese Academy of Meteorological Sciences, China Meteorological Administration, Beijing, China
ABSTRACT
The relationship between the Asian-Pacific oscillation (APO) and the tropical cyclone
frequency over the western North Pacific (WNP) in summer is preliminarily investigated through an
analysis of observed data. The result has shown clearly that APO is significantly and positively
correlated to the tropical cyclone frequency in the WNP. If APO is above (below) the normal in
summer, more (less) tropical cyclones will tend to appear in the WNP. The present study also
addresses the large-scale atmospheric general circulation changes underlying the linkage between
APO and the WNP tropical cyclone frequency. It follows that a positive phase of summer APO is
concurrent with weakened as well as northward and eastward located western Pacific subtropical
high (WPSH), low-level convergence and high-level divergence, and reduced vertical zonal wind
shear in the WNP, providing favorable environment for the tropical cyclone genesis, and thus more
tropical cyclones will come into being, and vice versa.
Keywords: Asian-Pacific oscillation, western North Pacific, tropical cyclone, atmospheric circulation
246
NUMERICAL SIMULATION AND PRECIPITATION ANALYSIS OF
TYPHOON BILIS (2007) AND KAEMI (2007)
ZHU Jian
Shaoxing Meteorological Office, Zhejiang Shaoxing, China
ABSTRACT
July 2006, Strong tropical storm Bilis(2007) and typhoon Kaemi(2007) landed in Fujian
Province. The two tropical cyclones were very similar on path, landing intensity and central
pressure. But Bilis had a broader raining regional than Kaemi. The impact on South China of Bilis
was far greater than Kaemi although Bilis was only a strong tropical storm. And this reason was
closely related to Bilis‟ long lifetime on land.
Bilis moved to west guided by easterly airstream south of subtropical high before its landing.
Cold air from the north could not be combined with the circulation of typhoon because of the
subtropical high. The westerly airstream was blocked in north of 40oN.Bilis had a very slow pace
and long lifetime after landing. A lot of wet warm air was transported into the typhoon circulation by
southwest monsoon and add to the energy attenuation of typhoon. The northerly airstream of Bilis‟
west side met southwest warm airflow from South China Sea at Nanling Mountains, and brought
heavy rain to Guangdong, Guangxi, Hunan and Jiangxi Province.
During the impact of Kaemi, the early situation was similar to Bilis.Later, Kaemi‟s residual
low-pressure connected with the north trough of low pressure at the east of Xi‟an City. Northern cold
air moved southward and the wet warm air moved northward by the way of
Jiangxi-Anhui-Shandong. Warm air and cold air met at Henan and Shandong, and heavy rainfall
caused serious flooding.
Numerical analysis showed that the moisture, dynamic and thermal conditions of Bilis was
better than Kaemi. The low-level jet offered moisture to the typhoon, and the continued supply of
water was very important to the typhoon‟s energy attenuation compensation. The configuration of
high-level divergence and low-level convergence formed a suction mechanism, which was
conducive to the maintenance of the typhoon strength. The frame of high-level positive helicity and
low-level negative helicity was a important reason of rainstorm. In the latter part of Bilis, the role of
Bilis was not the source of water vapor but to provide the uplift impetus conditions for the
precipitation. The southwest monsoon played the role of water vapor transmission. And the physical
mechanism of typhoons rainstorm was different with the general.
A forecast idea is summarized: (1) The typhoon landing on Fujian or Zhejiang Province will
move west under the guidance of easterly airstream in the south of subtropical high. If southwest
monsoon trough is very active, the wet warm air from southwest monsoon will add the loss of
typhoon energy and make a long-term maintenance of typhoon.So the precipitation in southern
China increase and the left side precipitation of typhoon path is greater. (2) If the subtropical high
weaken and east retreat and the westerly trough deepen and press south, the cold air will penetrate
into the typhoon circulation and increase the baroclinity of typhoon circulation. The precipitation will
increase significantly and the heavy rainfall may affect the northern region.
Keywords: rainstorm, numerical simulation, southwest monsoon, helicity, typhoon
247
THE RAINSTORM MECHANISM AND MOIST POTENTIAL
VORTICITY ANALYSIS OF SUPER TYPHOON WIPHA (2007)
ZHU Jian
Shaoxing Meteorological Office, Zhejiang Shaoxing, China
ABSTRACT
Typhoon Wipha (2007) moved to the northwest under the guidance of the southeast airflow
of the subtropical high marginal after generation. It landed in Zhejiang at 2:30 on September 19,
and then moved through Zhejiang Province, Anhui Province and Jiangsu Province. It moved into
the Yellow Sea finally. Because typhoon combined with the westerly trough, rain maintained for a
long time. Heavy rainfall attacked Zhejiang, Fujian, Jiangxi, Anhui, Jiangsu, Shanghai and
Shandong Province affected by the typhoon. And the largest wind speed was 55.3 m/sec in
Zhejiang‟s coastal.
Numerical simulation of typhoon Wipha was made, and the simulation resulted for
success.The moist potential vorticity was analyzed and the mechanism of rainstorm was
researched with the high-resolution simulation data. It was found that negative MPV1 on low level
had a positive correlation with rainstorm. The greater the absolute value of MPV1 the harder the
rain.MPV1 high-value associated with convection stable cold air.MPV1‟s low-value and
negative-value associated with warm and wet air which was convective instability. The evolution of
MPV showed the interaction of typhoon‟s wet warm air and dry cold air outside.MPV would be help
to the forecasting of typhoon‟s storm. When MPV1<0 and MPV2>0 in the lower troposphere, there
was a great probability of heavy rain.
The typhoon moved northward and combined with westerly trough. The dry cold air inserted
into warm air at the bottom and the baroclinic front zone formed where the  e contour was
intensive. The baroclinity increased and the cyclonic vortex enhanced. The wet baroclinic instability
triggered the release of the latent heat, which played a great role in developing and maintaining
heavy rain.
Positive MPV2 on 850hPa had a good relation with rainstorm district. A lot of wet warm air
from the sea was transported to the rainstorm district by low-level jet, and the rainstorm time was
extended. The strengthened low-level jet and the wet warm air would cause the increase of MPV2,
and the cyclonic vortex development, increasing the precipitation.
Keywords: rainstorm, numerical simulation, moist potential vorticity, slantwise vorticity development
248
World Weather Research Programme (WWRP)
Report Series
Sixth WMO International Workshop on Tropical Cyclones (IWTC-VI), San Jose, Costa Rica, 21-30 November
2006 (WMO TD No. 1383) (WWRP 2007 - 1).
Third WMO International Verification Workshop Emphasizing Training Aspects, ECMWF, Reading, UK, 29
January - 2 February 2007) (WMO TD No. 1391) (WWRP 2007 - 2).
WMO International Training Workshop on Tropical Cyclone Disaster Reduction (Guangzhou, China, 26 - 31
March 2007) (WMO TD No. 1392) (WWRP 2007 - 3).
Report of the WMO/CAS Working Group on Tropical Meteorology Research (Guangzhou, China, 22-24 March
2007) (WMO TD No. 1393) (WWRP 2007 - 4).
Report of the First Session of the Joint Scientific Committee (JSC) for the World Weather Research
Programme (WWRP), (Geneva, Switzerland, 23-25 April 2007) (WMO TD No. 1412) (WWRP 2007 – 5).
Report of the CAS Working Group on Tropical Meteorology Research (Shenzhen, China, 12-16 December
2005) (WMO TD No. 1414) (WWRP 2007 – 6).
Abstracts of Papers for the Fourth WMO International Workshop on Monsoons (IWM-IV) (Beijing, China, 20-25 October
2008) (WMO TD No. 1446) (WWRP 2008 – 1).
Proceedings of the Fourth WMO International Workshop on Monsoons (IWM-IV) (Beijing, China, 20-25 October 2008)
(WMO TD No. 1447) (WWRP 2008 – 2).