SiB3 Modeled Global 1-degree Hourly BiosphereAtmosphere Carbon Flux, 1998-2006
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Abstract
The Simple Biosphere Model, Version 3 (SiB3) was used to produce a
global data set of hourly carbon fluxes between the atmosphere and the
terrestrial biosphere for the years 1998-2006. These data represent the
global net ecosystem exchange of carbon dioxide between the planetary
boundary layer and the surface vegetation layer. Following atmospheric
convention, flux is defined as positive into the atmosphere and negative
into the surface vegetation.
The raw data are represented as hourly fluxes for 14637 land points. A
processing program [sib_process_flux.f90] is provided and can be used
in conjunction with a land mask [sib_mask.nc] to process the data into
hourly, daily-mean or monthly-mean fluxes on a global 1x1 degree
Cartesian grid. The monthly-mean SiB3 fluxes were compared to
TRANSCOM fluxes (Gurney et al., 2007) for years 2000-2005 as a
means of evaluating overall behavior of the model. In general, SiB3
fluxes are within the error bars of the TRANSCOM results.
These data are a carbon cycle reanalysis, which may be thought of as
analogous to NCEP meteorological reanalysis products. Carbon fluxes
have been used by a large community of atmospheric transport
modelers to create reanalysis of CO2 concentrations and the results have
been evaluated against observations. In addition, the reanalyzed flux
and CO2 fields are important for designing future observing strategies
for the global carbon cycle.
Background Information
Investigators:
Ian T. Baker ([email protected])
A. Scott Denning ([email protected])
Project:
Simple Biosphere Model, Version 3 (SiB3)
Atmospheric Science Department
Colorado State University
Data Set Title:
SiB3 Modeled Global 1-degree Hourly Biosphere-Atmosphere Carbon
Flux, 1998-2006
Site: �Global (gridded)
����������� Westernmost Longitude: -180 W
����������� Easternmost Longitude: 180 E
����������� Northernmost Latitude: 90 N
����������� Southernmost Latitude: -90 S
Data Set Citation:�
Baker, I. T. and A. S. Denning. 2008. SiB3 Modeled Global 1-degree
Hourly Biosphere-Atmosphere Carbon Flux, 1998-2006. Data set.
Available on-line [http://daac.ornl.gov/] from Oak Ridge National
Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee,
U.S.A.�doi:10.3334/ORNLDAAC/
Product Description:�
The spatial and temporal variations of CO2 flux in response to real
weather events are important for evaluating our understanding of carbon
exchange processes. This data set represents the global net ecosystem
exchange (NEE) of carbon between the atmosphere and the terrestrial
biosphere; specifically, the flux of CO2 between the planetary boundary
layer (PBL) and the surface vegetation layer. Following atmospheric
convention, flux is defined as positive into the atmosphere and negative
into the surface vegetation. The flux data were generated using the
Simple Biosphere Model, Version 3 (SiB3).
The raw data are represented as hourly fluxes for 14637 land points. A
processing program [sib_process_flux.f90] is provided and can be used
in conjunction with a land mask [sib_mask.nc] to cast the vector of land
points onto a global 1x1 degree Cartesian grid with hourly, daily-mean
or monthly-mean flux.
Data File Information:�
Raw hourly data are contained in files with the format:
SiB3.0_Cflux_YYYY_MM.nc
Where YYYY denotes year, and MM month. These files contain the
vectors (length 14637) of land-only data for each hour of the given
month. The 72 files are NetCDF formatted (about 40 mb each).
There is also a processing program [sib_process_flux.f90] and a
landmask file [sib_mask.nc]. The processing program reads the vector
of land points and scatters them to a global grid of hourly, daily or
monthly-mean fluxes. The landmask file provides locations of grid
centers for the global grid as well as mapping between the vector of
SiB3 points and the 2-dimensional global map.
There are no missing data. The entire grid is present for the years
included in this data set.
The data set was last modified 17 June 2008.
Methods and Materials:�
Model Description:�
The CO2 fluxes were created using the Simple Biosphere Model,
Version 3 (SiB3). SiB is based on a land-surface parameterization
scheme originally used to compute biophysical exchanges in climate
models (Sellers et al., 1986), but was later adapted to include ecosystem
metabolism (Sellers et al., 1996a; Denning et al., 1996a). The
parameterization of photosynthetic carbon assimilation is based on
enzyme kinetics originally developed by Farquhar et al. (1980), and is
linked to stomatal conductance and thence to the surface energy budget
and atmospheric climate (Collatz et al., 1991, 1992; Sellers et al.,
1996a; Randall et al., 1996). The model has been updated to include
prognostic calculation of temperature, moisture, and trace gases in the
canopy air space, and the model has been evaluated against eddy
covariance measurements at a number of sites (Baker et al., 2003;
Hanan et al., 2004; Vidale and Stöckli, 2005). SiB has been coupled to
the Regional Atmospheric Modeling System (RAMS) and used to study
PBL-scale interactions among carbon fluxes, turbulence, and CO2
mixing ratio (Denning et al., 2003) and regional-scale controls on CO2
variations (Nicholls et al., 2004; Corbin, 2005; Wang et al., 2007).
Other recent improvements include biogeochemical fractionation and
recycling of stable carbon isotopes (Suits et al., 2004), improved
treatment of soil hydrology and thermodynamics, and the introduction
of a multilayer snow model based on the Community Land Model (Dai
et al., 2003). Direct-beam and diffuse solar radiation are treated
separately for calculations of photosynthesis. The model is now referred
to as SiB3.
Historically, SiB has used prescribed vegetation parameters derived by
remote sensing (Sellers et al., 1996b). At global scales, this approach
allows realistic simulation of spatial and temporal variations in
vegetation cover and state (Denning et al., 1996; Schaefer et al., 2002,
2005). At the underlying pixel scale, however, phenology products
derived from satellite data must be heavily smoothed to remove
dropouts and artifacts introduced by frequent cloud cover. An inevitable
trade-off between cloud-induced “noise” in the leaf area and time
compositing systematically stretches the seasonal cycle by choosing
data late in each compositing period in spring, and early in each
composite in fall.
These simulations used 15-day Normalized-Difference Vegetation
Index (NDVI) data from (Tucker et al., 2005) to specify phenology.
Land cover classification is provided by data from Defries and
Townshend (1994). Following Los et al. (2000), we have removed
seasonal cycle from NDVI in broadleaf evergreen (tropical) forests. The
rationale is that the change in Leaf Area Index (LAI) or fraction of
absorbed Photosynthetically Active Radiation (fPAR) are small
compared to NDVI variability induced by cloud or aerosol masking.
Meteorological forcing is provided by NCEP
(http://www.cdc.noaa.gov/) 2-degree data regridded to a 1-degree
Cartesian grid. Driver data are available at 6-hourly increments,
interpolated to the 10-minute model time step. Radiation forcing is
normalized by solar zenith angle.
Data Processing:�
Annual NEE at each land point is constrained to be zero, following
Denning et al. (1996b).
Raw data are represented as hourly fluxes for 14637 land points. The
processing program [sib_process_flux.f90] can be used in conjunction
with the landmask [sib_mask.nc] to cast the vector of land points onto a
global grid with hourly, daily mean or monthly-mean flux.
Spatial Coverage:�
Global
Spatial Resolution:�
Fluxes are simulated on a 1x1 degree Cartesian grid. SiB operates on
land points only, of which there are 14637 on the 1x1 degree grid. A
landmask file [sib_mask.nc] provides locations of grid centers for the
global grid as well as mapping between the vector of SiB3 points and
the 2-dimensional global map.
Temporal Coverage:�
1998-2006
Temporal Resolution:�
Hourly
Data Usage Guidance:�
Quality Assurance and Quality Control:�
The monthly-mean SiB3 fluxes were compared to TRANSCOM flux
data available for years 2000-2005 (Gurney et al., 2007) as a means of
evaluating overall behavior of the model. These comparisons are shown
below (SiB3 model 2006 annual cycle is shown also). In general, SiB3
fluxes are within the error bars of the TRANSCOM results.
�
Several biases are apparent, particularly the tendency of SiB to overestimate wintertime efflux in Boreal North America, Boreal Asia,
Temperate North America, and Europe. This may be due in part to the
the constraint on SiB of an annual NEE of zero at all locations
(Denning et al, 1996b); there are no sources or sinks in SiB. There is
generally excessive model uptake in Boreal North America, insufficient
uptake in Temperate North America, and a 2-month lag in the seasonal
cycle in North Africa. In general, however, the comparison of SiB
fluxes to TRANSCOM fluxes is favorable.
Other Relevant Information about the Study:�
Funding for This Investigation:
This work has been supported by the National Science Foundation
Science and Technology Center for Multi-Scale Modeling of
Atmospheric Processes, managed by Colorado State University under
cooperative agreement No. ATM-0425247. It has also been supported
by NASA contracts NNX06AC75G SUPP1 (Atmospheric Modeling,
Assimilation and Source-Sink Estimation for the Carbon Cycle) and
NNG05GF41G #01 (Constraining the CO2 Missing Sink).�
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Point of Contact:�
Ian Baker
Atmospheric Science Department
Colorado State University
1371 Campus Delivery
Fort Collins, CO 80523-1371
Voice: 970-491-4948
Fax: 970-491-8449
Email: [email protected]
Revision Date:�Tuesday, July 22, 2008