Characterizing near-cloud aerosols using the MODIS ocean color product

Numerous studies have shown that clouds are surrounded by a several kilometer wide transition zone marked by strong variations in aerosol properties. This study examines the transition zone using the atmospheric correction parameters provided at 1 km resolution in the MODIS ocean color product: optical thickness and Angstrom exponent.

First, the study explores the way ocean data quality assessment flags may help atmospheric studies in balancing the competing needs for dense sampling and high accuracy. Using an optimal set of QA flags in examining a large region over the North Atlantic Ocean, the study then shows that optical thickness and particle size are systematically higher near clouds. Theoretical simulations show that the differences have strong radiative impacts that are especially large if the higher optical thicknesses are caused by aerosol particles as opposed to undetected cloud particles. The results imply that considering near-cloud areas and understanding the causes of near-cloud particle changes are critical for accurate calculations of aerosol radiative forcing.