Simulations of Cloud/Radiative Responses to Variations in Cloud Condensation Nuclei (CCN)

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9529321 Cotton In this project, the principal investigator and colleagues will examine some of the proposed mechanisms by which anthropogenic cloud condensation nuclei (CCN) may alter the microstructure, macrostructure, and radiative properties of marine stratocumulus clouds. The research should provide important insights necessary for the development of improved parameterization of aerosol/cloud microphysics/ cloud dynamics interactions that can be used in large-scale atmospheric models. The research involves the application of a sophisticated large eddy simulation (LES) model with explicit, bin-resolving microphysics (EM). The approach will be to perform cloud-resolving simulations of cases observed during the Atlantic Stratocumulus Transition Experiment (ASTEX) and to evaluate the credibility of those simulations by comparing the simulated data with observed cloud features. The PI will also perform sensitivity experiment in which the concentrations and vertical profiles of CCN are varied. From these simulations, he hopes to determine if modest increases in concentrations of CCN directly alter cloud albedo significantly, or alter cloud coverage, or alter entrainment in the cloud boundary layer, or whether the marine boundary layer may be bistable with respect to the production rates of CCN. This project is being supported as a contribution to NSF's Role of Clouds, Energy, and Water in Global Climate Change (ROCEW) Program. ***