Evaluation of GEOS-CHEM Aerosol Optical Thicknesses : comparisons to satellite data for 2003
S. Generoso & I. Bey
LMCA, EPFL, Lausanne, Switzerland
Acknowledgements : F.M: Bréon (POLDER data),
Q. Li & R. V. Martin (Data for the Mie calculation)
T2 : projet / questions scientifiq
We plan to use GEOS-CHEM to ...
1. Characterize aerosol distributions (e.g. anthro. vs natural) / focus over the Asian continent and Pacific/Indian Oceans
2. Investigate processes (e.g. emission heights, deposition, transport …)
comparisons with multi observations (satellites, ground-based measurements)
T2 : projet / questions scientifiq
The method chosen to start
Year 2003 : Both POLDER & MODIS data
Large interannual aerosol events in Asia during spring/summer 2003 (to characterize)
Data : POLDER, MODIS, AERONET … (others are welcome)
GEOS-CHEM : version used v07-02-03
Resolution 2°x 2.5°
30 levels
GEOS 4
GEOS-CHEM : version v07-02-03
Modifications for this study :
--> AOT @ 550 & 865 nm on-line
--> biomass burning emissions for 2003 based on ATSR fire counts
ATSR fire count and emission inventories
Adapted from Generoso et al, ACP, 2003
Definition of “homogeneous” regions
An emission constant (g/detected fire) computed for each region
ATSR fire counts (night time)
Available 07/96 => 10/03
annual emission used in GEOS-CHEM
(XXX.bioburn. seasonal.geos.2x25)
Seasonal cycle, Interannual variations and Spatial distribution follow satellite observation
Emitted quantities depend on the inventories used
T2 : projet / questions scientifiq
Differences introduced in the BB emissions used in GEOS-CHEM ...
OC in kg /year (x 1010)
“ATSR” “CURRENT”
2000 1.70 2.11
2002 2.25 2.67
2003 2.00 2.34 (CLIM)
CURRENTLY USED IN GEOS-CHEM v-07-02-03
THIS STUDY
… in terms of emitted quantities :
… in terms of spatial distribution
CLIM
THIS STUDY
OCPO Emissions JUNE 03
kg /month
1.4 x 108 kg
7.3 x 108 kg
The POLDER mission
(Polarization and Directionality of the Earth Reflectance)
POLDER-1 : Nov 96 to Jun 97
POLDER-2 : Apr 03 to Oct 03
(On ADEOS)
Originality : polarization - over ocean and land
~ column aerosol load in the fine mode
Classical method - Over ocean only
AOT ~ column aerosol load
May 2003
Fine mode AOT
Total AOT
(Aerosol Optical Thickness)
Comparisons to POLDER AOT : FINE mode
Sulf + BC + OC + SSac
Overestimate in Northern Hemisphere (mainly sulfates over Europe)
Underestimate in B.B. regions
Comparisons to POLDER AOT: COARSE mode
DUST + SSc
Underestimate in Bay of Bengal
Dust export to Atlantic rather well represented
Conclusions
1. Biomass Burning emissions for 2003 available
May be underestimated
Can be provided when the ATSR data are available (from 96/07 to 03/10)
2. AOT @ 550 & 865 nm available
3. 1st comparisons to satellite data show that there is a lot to investigate
🡪 Dust export to Atlantic rather well represented
Additional slides
T2 : projet / questions scientifiq
... in terms of seasonal cycles
month
OC in kg C
Clim
2003 “ATSR”
2002 “ATSR”
2002 “Current”
Spatial distribution … modified
initial
ATSR 98
ATSR 00
Burnt Area 00
Better agreement with burnt area observations
ATSR vs other biomass burning sat. products
Sahel
Indonesia
North Australia
South America
ATSR
AVHRR
TRMM
GLOBSCAR
GBA2000
The ATSR night time restrictions show a seasonal cycle that is consistent with the other proxies