Retrieving the effective radius of Saharan dust coarse mode from AIRS

Abstract

We show that the effective radius of the dust coarse mode can be retrieved from Aqua/AIRS observations, using a two step process. First, for each AIRS observation, the dust infrared optical depth, the mean altitude of the dust layer and an estimate of the temperature and water vapor profiles are obtained from 8 spectral channels, using a Look‐Up‐Table approach. Second, the effective radius is obtained from an additional AIRS channel (located at 9.32 μm), selected for its sensitivity to dust particle size and its insensitivity to dust particle shape or to other potential contaminants (ozone, for example). The dust coarse mode effective radius is retrieved from AIRS over the Atlantic Ocean for the period April to June 2003. It compares well with in situ measurements, transport model simulations and sun‐photometer retrievals. We find that the coarse mode effective radius decreases slightly with transport distance, from 2.4 μm to about 2 μm.