Closure Assumptions in the Cumulus Parameterization Problem

Abstract

Physical processes associated with condensation of water vapor are inherently nonlinear and, therefore, their collective effects can directly interact with larger-scale circulations. But most individual clouds, in which condensation takes place, are subgrid-scale for the conventional grid size of general circulation and numerical weather prediction models. Then, for a set of model equations to be closed, we must formulate the collective effects of subgrid-scale clouds in terms of the prognostic variables of grid scale. This is the problem of cumulus parameterization in numerical modeling of the atmosphere.