RAIN PRODUCTION IN CONVECTIVE CLOUDS AS SIMULATED IN AN AXISYMMETRICAL MODEL WITH DETAILED MICROPHYSICS .1. DESCRIPTION OF THE MODEL

A hydrodynamic nonhydrostatic anelastic numerical model of an axisymme tric convective cloud is described in which the microphysical processe s are treated in detail for different species of hydrometeors: drops, ice crystals, graupel, and snow particles. The size distribution funct ion for each type of particle is divided into 34 spectral bins. In eac h spectral category two physical moments of the distribution function (number and mass concentration) are independently calculated using the method of moments. The following physical processes are computed: nuc leation of drops and ice crystals, freezing of drops, diffusional grow th/evaporation of drops and ice particles, collisional coalescence of drops and ice particles, binary breakup of drops, melting of ice parti cles, and sedimentation. The model describes the different stages of c loud development, the formation of ice, its growth by deposition and r iming, the formation of graupel, and the precipitation stage. Analysis of the distribution functions for the different species provides insi ght into the different microphysical processes active in rain formatio n in mixed clouds. As an illustration of the capability of the model, the simulation of a mixed-phase continental cloud is presented.