Aerosol Direct Radiative Effect from OMI Concept and First Results

2008 OMI Science Team Meeting, Helsinki, Finland

Aerosol Direct Radiative Effect from OMI

Concept and First Results

B. Veihelmann, P. Wang, J.P. Veefkind, P.F. Levelt

Royal Netherlands Meteorological Institute

2008 OMI STM, Helsinki, Finland Slide 2

B.Veihelmann, Royal Netherlands Meteorological Institute (KNMI)

Overview

Aerosol Direct Radiative Effect (DRE)

at the top of the atmosphere from OMI Concept Comparison with reference data 2 nice images Conclusions



Concept

multi-wavelength algorithm (OMAERO product) radiance in 14 wavelength bands, 340-500 nm Aerosol Optical Thickness (AOT)

best fitting aerosol model (out of 50 models)

refractive index, size distribution, height

model atmosphere of best fitting aerosol model upwelling flux at TOA Direct Radiative Effect DRE = flux() – flux(fit)



Concept

fluxes at TOA parameterized

precalculations with Doubling Adding Code KNMI (DAK) spherical albedo S transmission term T flux at top of the atmosphere for black surface Fpath

efficient flux calculations for any given Lambertian surface albedo a sun-satellite geometry elevation

)1( aS

aTFF pathTOA



Comparison with reference data EUCAARI intensive observation phase

cloud - aerosol measurement campaign May 2008 at Cabauw, the Netherlands

radiative transfer simulations AOT & SSA from ground-based sun-photometer profiles from radiosondes excellent agreement with ground-based

measurements of broad-band flux

=> reference for DRE from OMI -range 362-452 nm at top of atmosphere



Simulations for Cabauw

site

OMI

Nearest pixel

OMI

average 50 km radius

OMI

average 50 km radius

Albedo consitent with Cabauw data

consitent with Cabauw data

consitent with Cabauw data

from climatology

Flux TOA W/m2 30.4 29.7 31.1 30.1

DRE TOA W/m2 -3.6 -3.6 -5.0 -2.2

AOT 0.2 0.2 0.4 0.1

Vertical dist. 0-1 km 0-2 km 0-2 km 0-2 km

SSA 484 nm 0.89 0.95 0.95-0.97 0.95

Comparison with reference data



March 2006 aerosol transport event

0 2 4 6 8AOT

-40 -30 -20 -10 0DRE (W/m2)

sun-glint



Conclusion DRE at TOA from OMI?

first test indicates that numbers are meaningful relevance of DRE in UV-VIS?

340-500 nm ~15% of irradiant solar energy percentage of DRE larger:

aerosol scattering & absorption ~ -a

Rayleigh scattering enhances absorption by aerosols sensitivity to surface albedo

ocean BRDF implementation envisaged land BRDF?

cloud screening using independent information MODIS cloud mask?

Aerosol Direct Radiative Effect from OMI Concept and First Results

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