Mineral dust plume evolution over the Atlantic from MISR and MODIS aerosol retrievals

We demonstrate how Multiangle Imaging Spectroradiometer (MISR) and Moderate Resolution Imaging Spectroradiometer (MODIS) space-based aerosol products provide complementary information, characterizing (1) transported desert dust plume extent over water, (2) aerosol optical thickness (AOT) evolution, and (3) particle size sensitivity and fraction spherical evolution for the thicker parts of these plumes. MODIS provides more extensive coverage, whereas MISR’s multiangle retrievals include dust properties and fill in areas where glint precludes MODIS optical depth retrievals, increasing by up to 50% dust plume surface area coverage compared to MODIS-only observations. These results can be used to improve dust aerosol representations in climate, forecast, and transport models. Extensive comparison of MISR and MODIS AOT retrievals with Aerosol Robotic Network (AERONET) observations in dusty regions show accuracies of about 20%; MISR Angstrom exponent is predominantly less than 1, in reasonably good agreement with AERONET. For four selected North African dust transport events, combined MISR and MODIS observations map systematic changes in retrieved plume surface area, on the basis of AOT contours; these reflect differences in aerosol dispersion and removal rates that must be reproduced by models. Within MISR retrieval uncertainties, Angstrom exponent and AOT fraction spherical are lower in the optically thicker parts of the plume by up to 30% and increase as the plume is transported across the ocean, as would be expected; retrieved single-scattering albedo values are $0.98 for all stages of plume evolution. For the cases studied, AERONET shows similar property patterns at points on either side of the Atlantic and indicates $15% decrease in aerosol coarse mode effective radius during transoceanic transport.