Partitioning Mass, Heat, and Moisture Budgets of Explicitly Simulated Cumulus Ensembles into Convective and Stratiform Components

Abstract

Simulated data from the UCLA Cumulus Ensemble Model (CEM) are analyzed to partition mass, heat, and moisture budgets of cumulus ensembles into convective and stratiform components. A method based primarily on the horizontal distribution of maximum cloud draft strength below the melting level in a CEM grid column has been developed for this analysis. The stratiform region includes both precipitating and nonprecipitating anvils. The convective and stratiform components of mass, heat, and moisture budgets are distinctly different, in qualitative agreement with previous observational and modeling studies. In the heat and moisture budgets, the difference is due mainly to that in the phase change processes. In general, condensation/deposition dominate evaporation/sublimation in the convective region. All of these processes are more or less equally important in the stratiform region. Freezing occurs only in the convective region. Sublimation from snow/graupel in the stratiform region is much more important than in the convective region. Radiative effects in the stratiform component of the heat budget are as important as effects of phase changes, while radiative effects in the convective component are far less significant. The importance of the convergences of eddy fluxes, especially in the moisture budget, is confirmed. The convergences in the stratiform component are found to be parameterizable only if the vertical motions and the properties of both mesoscale updrafts and mesoscale downdrafts are known. The horizontal inhomogeneity within mesoscale updrafts/downdrafts is of secondary importance for parameterizing the convergences of eddy fluxes in the stratiform component.