A Stratocumulus Model with an Internal Circulation

Abstract

An updraft and downdraft circulation model based on a mass flux representation of convective fluxes is incorporated into a classic cloud-topped, mixed layer model. The convective mass flux is assumed to be proportional to the convective velocity scale. The closure is obtained by assuming that the turbulent kinetic energy consumption due to entrainment is a small portion of its production due to buoyancy. The model is used to study how cloud-top entrainment instability, partitioning or radiative cooling, and drizzle affect the boundary layer, and the stratocumulus circulation. The results obtained with the model indicate that the intensity of the internal circulation may be critical in regulating the structure of stratocumulus clouds so that the cloud-top entrainment instability as it is presently used is not sufficient to define the breakup of stratocumulus. The vertical distribution of radiative cooling in the mixed layer is found to decrease the amplitude of the diurnal cycle of the cloud thickness. Precipitation processes are incorporated into the model to study their effects on the bulk properties of the boundary layer.