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 Characterize aerosol distributions (e.g. anthro. vs natural) / focus over the Asian continent and Pacific/Indian Oceans 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 v Resolution 2°x 2.5° 30 levels GEOS 4 GEOS-CHEM : version v Modifications for this study : --> 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 ) “ATSR”“CURRENT” (CLIM) CURRENTLY USED IN GEOS-CHEM v THIS STUDY … in terms of emitted quantities :

… in terms of spatial distribution CLIM THIS STUDY OCPO Emissions JUNE 03 kg /month 1.4 x 10 8 kg 7.3 x 10 8 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 Biomass Burning emissions for 2003 available May be underestimated Can be provided when the ATSR data are available (from 96/07 to 03/10) & 865 nm available 3. to investigate 3. 1 st comparisons to satellite data show that there is a lot to investigate  Overestimation of fine mode AOT in Northern Hemisphere (mainly sulfates)  Underestimation of fine mode AOT in BB regions  Underestimation of coarse mode AOT in Bay of Bengal  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 Australi a South America ATSR AVHRR TRMM GLOBSCAR GBA2000 The ATSR night time restrictions show a seasonal cycle that is consistent with the other proxies