Abstract
The structure of vorticity fields of cumulus clouds is studied using a three-dimensional numerical convection model developed by Clark (1977, 1979. 1981). The analysis of the model results suggests that 1) it is justified to neglect the solenoidal effect in cloud vorticity dynamics; and 2) the effects of vertical advection and twisting of vorticity, while both are very important to the local structure, cancel each other when averaged over a cloud horizontal cross-section. Consequently, 3) the cloud vorticity in the mean is controlled mainly by horizontal convergence/divergence of vorticity through cloud boundary and satisfies a very simple conservation equation. Furthermore, the model results also suggest that 4) clouds can induce a very strong horizontal eddy flux of vertical vorticity. The magnitude of this flux is of the order 10−4 m s−2 on the basis of a unit fractional cloud coverage. These results support the hypothesis introduced by Cho and Cheng (1980).
