On the Factors Controlling the Development of Shallow Convection in Eddy-Diffusivity/Mass-Flux Models

Abstract

This study addresses key aspects of shallow moist convection, as simulated by a multiplume eddy-diffusivity/mass-flux (EDMF) model. Two factors suggested in the literature to be essential for the development of convective plumes are investigated: surface conditions and lateral entrainment. The model consistently decomposes the subgrid vertical mixing into convective plumes and the nonconvective environment. The modeled convection shows low sensitivity to the surface plume area. The results indicate that plume development in the subcloud layer is controlled by both surface conditions and lateral entrainment. Their impact significantly changes in the cloud layer where the surface conditions are no longer important. The development of shallow convection is dominated by the interactions between the plumes and the large-scale field and is sensitive to the representation of the variability of thermodynamic properties between the plumes. A simple two-layer model of steady-state convection is proposed to help understand the role of these processes in shaping the properties of moist convection.