Net radiative effect of dust aerosols from satellite measurements over Sahara

Abstract

The clear‐sky aerosol top of atmosphere shortwave (SW) and longwave (LW) radiative effects over the Saharan desert (15–30°N, 10°W–30°E) are investigated based entirely on the satellite observations of aerosol optical thickness (AOT), surface albedo, surface temperature, surface emissivity, atmospheric water vapor content, and SW/LW fluxes. The Ozone Monitoring Instrument (OMI) on Aura and the Multi‐angle SpectroRadiometer (MISR) on Terra satellite are used to estimate AOT at 558 nm (EAOT) for June to September, 2005–2006 when the predominant aerosol type is dust. We then use these EAOT values in conjunction with broadband measurements from the Clouds and the Earth's Radiant Energy System (CERES) to calculate the top‐of‐atmosphere SW and LW flux radiative effect due to these aerosols. The difference in SW flux between desert surface and dust aerosols is found to be negligible due to the high surface reflectance over the Sahara desert. The instantaneous area‐averaged LW radiative effect is calculated as +11.4 Wm−2 with radiative efficiencies ranging from +11 to +26 Wm−2/AOT. The results indicate that net radiative effect of dust over the Sahara desert is dominated by the longwave effect in contrast to oceans where the shortwave effect dominates.