Cloud-base fluxes in the cumulus-capped boundary layer

A closure for the fluxes of mass, heat, and moisture at cloud base in the c umulus-capped boundary layer is developed. The cloud-base mass flux is obta ined from a simplifed turbulence kinetic energy (TKE) budget for the sub-cl oud layer, in which cumulus convection is assumed to be associated with a t ransport of TKE from the sub-cloud layer to the cloud layer. The heat and moisture fluxes are obtained from a jump model based on the vi rtual-potential-temperature equation. A key part of this parametrization is the parametrization of the viaual-temperature flux at the top of the trans ition zone between the sub-cloud and cloud layers. It is argued that pressure fluctuations must be responsible for the transpo rt of TKE from the cloud layer to the sub-cloud layer.