NASA - National Aeronautics and Space Administration

This paper examines the potential effects of Saharan dust intrusions on the microphysical structure and optical properties of anvil-cirrus clouds. A series of 3-D LES simulations were initialized and forced by output data from mesoscale simulations in a previous study, in which we analyzed the impact of the enhanced low-level concentrations of cloud-nucleating aerosols on the characteristics of convective storms. The effects of enhancing aerosol concentrations on the ice-particle size distributions as well as some of their moments were analyzed as the LES model domain followed the trajectory of the simulated cirrus cloud. The experimental design was based on aerosol concentrations observed over the peninsula of Florida toward the end of the CRYSTALFACE field campaign held during July 2002.

Results indicate that variations in the concentrations of nucleation aerosols have a significant effect on the optical properties and lifetime of cirrus anvil clouds. In addition, enhancing low-level aerosols can affect the radiation budget, leading to surface radiative cooling. Both IFN and CCN enhancements show important effects; however, results suggest that CCN and GCCN play a more dominant role.