Evaluation of GEOS-CHEM Evaluation of GEOS-CHEM Aerosol Optical Thicknesses : Aerosol Optical Thicknesses : comparisons to satellite data comparisons to satellite data

for 2003for 2003

S. Generoso & I. Bey

LMCA, EPFL, Lausanne, SwitzerlandLMCA, EPFL, Lausanne, Switzerland

Acknowledgements Acknowledgements : F.M: Bréon (POLDER data),: F.M: Bréon (POLDER data),

Q. Li & R. V. Martin (Data for the Mie calculation)Q. Li & R. V. Martin (Data for the Mie calculation)

T2 : projet / questions scientifiq

We plan to use GEOS-CHEM to ...We plan to use GEOS-CHEM to ...

1.1. Characterize aerosol distributions (e.g. anthro. vs natural) / focus over the Asian continent and Pacific/Indian Oceans

2.2. Investigate processes (e.g. emission heights, deposition, transport …)

comparisons with multi observations (satellites,

ground-based measurements)

T2 : projet / questions scientifiq

The method chosen to startThe 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 ATSR fire count and emission inventoriesinventories

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 Differences introduced in the BB emissions used in GEOS-CHEM ...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 in terms of terms of spatial spatial

distributidistributiononCLIM

THIS STUDY

OCPO Emissions JUNE 03

kg /month

1.4 x 108 kg

7.3 x 108 kg

The POLDER missionThe POLDER mission(Polarization and Directionality of the Earth Reflectance)

POLDER-1 : Nov 96 to Jun 97POLDER-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 AOTTotal AOT

(Aerosol Optical Thickness)

Comparisons Comparisons to POLDER to POLDER AOT : FINE AOT : FINE

modemode

Sulf + BC + OC + SSac

Overestimate in Northern Hemisphere (mainly sulfates over

Europe)

Underestimate in B.B. regions

Comparisons to Comparisons to POLDER AOT: POLDER AOT: COARSE modeCOARSE mode

DUST + SSc

Underestimate in Bay of Bengal

Dust export to Atlantic rather

well represented

ConclusionsConclusions

1.1. Biomass Burning emissions for 2003 available

May be underestimated

Can be provided when the ATSR data are available (from 96/07 to 03/10)

2.2. AOT @ 550 & 865 nm available

3.3. 1st comparisons to satellite data show that there is a lot to investigateto investigateOverestimation 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 slidesAdditional slides

T2 : projet / questions scientifiq

... in terms of seasonal cycles... in terms of seasonal cycles

month

OC

in

kg

C

Clim

2003 “ATSR”

2002 “ATSR”

2002 “Current”

Spatial distribution … modifiedSpatial distribution … modified

initial

ATSR 98

ATSR 00

Burnt Area 00

Better agreement with burnt area Better agreement with burnt area observationsobservations

ATSR vs other biomass burning sat. ATSR vs other biomass burning sat. productsproducts

Sahel

IndonesiaNorth Australia

South America

ATSR AVHRR TRMM

GLOBSCAR GBA2000

The ATSR night time restrictions show a The ATSR night time restrictions show a seasonal cycle that is consistent with the other seasonal cycle that is consistent with the other

proxies proxies