Methode de representation de la turbulence d'echelle inferieure a la maille pour un modele tri-dimensionnel de convection nuageuse

Abstract

Significant improvements are occurring in the representation of physical processes in atmospheric convection models. They should go along with parallel improvements in the parameterization of subgrid scale turbulent processes. This problem appears to be particularly delicate in the presence of clouds, due to the local release of latent heat. Two important points are the choice of adequate turbulent thermodynamic variables and of the method for truncating the statistical moment equations. These topics are discussed here within the framework of the three-dimensional convection model under development at the Laboratoire de Meteorologie Dynamique. Assuming the need for at least a simplified second-order closure, two improvements are tested on a numerical simulation of the Porto Rico experiment conducted by the National Center for Atmospheric Research (U.S.A.) in 1972. They concern the use of a rate equation for sub-grid scale turbulent kinetic energy and of specific variables which are approximately conserved in the condensation process.