TOWARD CLOUD RESOLVING MODELING OF LARGE-SCALE TROPICAL CIRCULATIONS - A SIMPLE CLOUD MICROPHYSICS PARAMETERIZATION

This paper discusses cloud microphysical processes essential for the l arge-scale tropical circulations and the tropical climate, as well as the strategy to include them in large-scale models that resolve cloud dynamics. The emphasis is on the ice microphysics, which traditional c loud models consider in a fairly complex manner and where a simplified approach is desirable. An extension of the classical warm rain bulk p arameterization is presented. The proposed scheme retains simplicity o f the warm rain parameterization (e.g., only two classes of condensed water are considered) but introduces two important modifications for t emperatures well below freezing: 1) the saturation conditions are pres cribed based on saturation with respect to ice, not water; and 2) grow th characteristics and terminal velocities of precipitation particles are representative for ice particles, not raindrops. Numerical tests s uggest that, despite its simplicity, the parameterization is able to c apture essential aspects of the cloud microphysics important for the i nteraction between convection and the large-scale environment. As an e xample of the application of this parameterization, preliminary result s of the two-dimensional cloud-resolving simulation of a Walker-like c irculation are presented.