Wet Equivalent Potential Temperature and Enthalpy as Prognostic Variables in Cloud Modeling

Abstract

The bulk thermodynamic consequences of nonreversible phase changes and of the precipitation process are emphasized. Two predictive quantities are proposed, either of which can be used as a prognostic thermodynamic variable, instead of temperature or of potential temperature, in numerical models of convective clouds. The use of these new variables decreases the coupling between the dynamical and the thermodynamical equations and is shown to induce smaller errors under most circumstances involving physical processes such as the freezing of supercooled drops and the evaporation in undersaturated air. The respective advantages of both variables are discussed; the choice between them is shown to depend upon the phenomena to be simulated.