A Cumulus Parameterization for Climate Studies of the Tropical Atmosphere. Part I: Model Formulation and Sensitivity Tests

Abstract

A scheme for parameterizing the effects of cumulus convection for the maintenance of the thermodynamic structure of the tropical atmosphere is described. This parameterization is used in a one-dimensional model that represents the vertical structure of the atmosphere as a function of Chebyshev polynominals. The convective fluxes in this model are represented as a product of an ?effective? convective mass flux and cloud-environment differences in thermodynamic properties for a reference cloud. The conversion of cloud water to precipitation is assumed to be proportional to the cloud water content. The effects of shallow clouds on the thermodynamic structure new cloud base are represented by constraining the derivative of the mass flux near cloud base. An equilibrium assumption is used to obtain the mass flux associated with deep clouds. The sensitivity of the vertical distributions of the parameterized heating and moistening rates to cloud model assumptions is determined. The inefficient conversion of cloud water to precipitation significantly cools and moistens the upper portion of the cloud layer. The evaporation of rain significantly cools the lower layers, although in the moisture budget the evaporation of rain is less important than other effects. The importance of shallow clouds for maintaining the heat and moisture budgets near cloud base is clearly demonstrated.