Aerosol Replenishment and Cloud Morphology: A VOCALS Example

Abstract

he impact of aerosol replenishment in a stratocumulus-topped boundary layer (STBL) on cloud morphology and albedo is examined using a large-eddy simulation (LES) model in conjunction with a prey?predator-type dynamical model following Koren and Feingold. In both the LES and the prey?predator models, the aerosol replenishment is represented as a relaxation term toward an ambient aerosol concentration with a time scale . The LESs suggest the existence of three distinct cloud regimes corresponding to different aerosol relaxation times. Specifically, for a small , the simulations are characterized by a large aerosol concentration, weak precipitation, relatively thick cloud depth, and closed cells. For a moderate , the simulated clouds exhibit open cellular patterns, in accordance with low aerosol concentration and moderate precipitation that oscillates in time. For a large , the aerosol may be depleted by intense drizzling and accordingly the cloud disappears. The critical aerosol relaxation times that separate these regimes vary with the ambient aerosol number concentration and cloud depth. Solutions from the low-order dynamical model with parameters relevant to the LESs are in general consistent with the LES results and provide further insight into the interplay among clouds, aerosol, and precipitation.