Micro- and Macro-Structures of Numerically Simulated Convective Clouds

Abstract

This article describes four numericals experiments in Moist convection conducted by means of a two-dimensional dynamic model. In addition to the usual macrophysical processes included in such models, it incorporates the microphysical processes governing condensation and handles the interactions between the two types of processes. More specifically, the model predicts supersaturation, droplet growth, size spectra, liquid water content, excess temperature, motion, and dynamic pressure at 961 grid points. Convection is initiated by means of a bubble which is buoyant because of excess temperature and, in one case, excess momentum as well. Condensation takes place on a specified population of sodium chloride nuclei representing maritime conditions. Results are compared with field observations of maritime cumuli near the eastern Australian coast and continental cumulus mediocris near Flagstaff, Ariz. In many respects, there are close similarities between the natural and simulated clouds including a remarkably close agreement between observed and computed dispersion coefficients. On the whole, this comparison of observed and simulated cloud data is most encouraging to further experiments in cloud simulation. Coalescence was not incorporated into the main computer program, but some coalescence experiments were run for a single-parcel model. These experiments showed that had coalescence been included in the two-dimensional model, it would have produced rain in some of the clouds within a span of 20?30 min.