Methode de representation de la turbulence associee aux precipitations dans un modele tri-dimensionnel de convection nuageuse

Abstract

A method is presented for the parameterization of subgrid-scale processes in the framework of a three-dimensional micro-scale model which simulates the initiation of precipitation in the planetary boundary layer. The method uses truncated second-order moment equations which involve combinations of dynamical, thermodynamical and water variables; the water variables include water vapor, cloud droplets and rain water, with the hypothesis of a Marshall-Palmer raindrop distribution. The method is applied to the case of a trade-wind cumulus layer where water vapor content is artificially increased. As some approximations concerning the water variables are not easy to verify by experimental methods, results should be considered only as indicative; they show the extent to which a more complete parameterization of subgrid-scale processes may compensate for the inevitable lack of spatial resolution in an atmospheric boundary-layer model.