Aerosol retrievals from MSG SEVIRI over ocean using AVHRR-like algorithm

The current operational algorithm used to retrieve aerosol optical depth and Ångström exponent over ocean from the solar reflectance bands of the Advanced Very High Resolution Radiometer (AVHRR) flown onboard NOAA polar orbiting satellites has been adapted to the corresponding channels of the Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) flown onboard the Meteosat Second Generation (MSG) geostationary platform. By examining two specific dust events from 3-5 March and 12-13 October 2004 we show how a detailed description of the dust loading through the diurnal cycle can be obtained. Snapshot comparisons with spatially resolved retrievals from the MODerate resolution Imaging Spectrometer (MODIS) instruments flown on the Terra and Aqua polar platforms show qualitative agreement with SEVIRI retrievals. In addition to the generic aerosol model used in the NOAA/NESDIS algorithm, which was tuned to optimize retrievals over global ocean, three microphysical models, specifically proposed in the aerosol literature for desert dust, have also been tested. Comparisons of the diurnal variation seen in the SEVIRI retrievals with available ground based Aerosol Robotic Network (AERONET) observations from two coastal stations suggests that the phase functions associated with these three dust representations result in unrealistic time dependent behavior. This tendency is removed when the more generic aerosol representation used in the NOAA/NESDIS algorithm is employed.