Statistical Analysis of Cumulonimbus Anvil and Surrounding Aerosol Properties Retrieved by MODIS in Subtropical and Tropical Regions

In a contribution to a study of the factors controlling cumulonimbus anvil crystal size, here we present a statistical analysis of MODIS cloud and aerosol data from southern Florida, where the CRYSTAL-FACE field campaign took place in 2002, and a region from the central Pacific. We have developed simple algorithms that identify monolithic anvil shields and their more likely core regions, as well as aerosol data within a specified distance from the anvil shield edges. We then calculate relevant statistical properties of each anvil and its associated aerosols, including minimum effective cloud particle radius and peak aerosol optical depth. Choosing the July 2002 time period for Florida and the March 2004 time period for the tropical Pacific, we find that useful data on convection in both regions is provided only by the Aqua platform. Initial results show a slight decreasing trend of cloud particle size with aerosol optical depth in Florida and a slight increasing trend in the Pacific. The Pacific exhibits a wider range of aerosol optical depths and minimum and peak cloud particle radii than Florida. However, the greater anvil size and extent of low-cloud coverage limit successful aerosol retrievals over the central Pacific significantly more than over southern Florida, where aerosol data is often robust. Significant day-to-day variation in aerosol optical depth and cloud particle size is present in both regions, suggesting that these areas are well suited for studying the effects of varied aerosol regimes on cloud development. Using cases identified with MODIS retrievals as described here, future work will focus on the use of a mesoscale model with detailed cloud and aerosol microphysics to decouple aerosol and meteorological influences on anvil cloud properties.