A New Parameterization for Shallow Cumulus Convection and Its Application to Marine Subtropical Cloud-Topped Boundary Layers. Part I: Description and 1D Results

Abstract

A new parameterization of shallow cumulus convection is presented. The parameterization consists of a mass flux scheme based on a buoyancy-sorting, entrainment?detrainment plume model. The mass flux scheme is coupled to a 1.5-order turbulence closure model with an entrainment closure for convective boundary layers. Model performance is verified using single-column-model simulations at relatively high vertical resolution of pure trade-cumulus convection and a cumulus to stratocumulus transition. Mixing rates, cloud cover, and vertical flux profiles, as deduced from previously published large-eddy simulation studies, are well reproduced by the parameterization. The model is used to demonstrate that height variations of lateral mixing rates can be successfully captured by a simple implementation of a buoyancy-sorting mechanism in the updraft cloud model. A companion paper describes the implementation of the scheme in a mesoscale model.