Satellite-based assessment of cloud-free net radiative effect of dust aerosols over the Atlantic Ocean

Abstract

Using eighteen months (June-August, 2000-2005) of spatially and temporally collocated Moderate Resolution Imaging Spectroradiometer (MODIS) and the Clouds and the Earth's Radiant Energy System (CERES) data from the Terra satellite over the Atlantic Ocean [10W-60W, 0-30N], we first separate the dust aerosol optical thickness at 0.55 μm (AOT) from the total column MODIS AOT. We then calculate the cloud-free TOA net radiative effect (NRE) of dust aerosols by accounting for diurnal effects and sample biases. The cloud-free NRE is -6.31 ±1.16 WM-2 and nearly twenty percent of the shortwave radiative effect (-7.75 ± 0.86 WM-2) is cancelled by the longwave radiative effect (+1.44 ± 0.57 Wm-2) indicating the importance of the dust aerosols in the thermal portion of the electromagnetic spectrum. This is the first multi-year satellite-based assessment of the NRE of dust aerosols indicating the importance of both the shortwave and longwave radiative effects of dust aerosols over the oceans unlike anthropogenic aerosols that have negligible TOA longwave radiative forcing effects. Copyright 2007 by the American Geophysical Union.