Case studies of frictional dissipation in numerically simulated clouds

Abstract

The effects of parameterized eddy diffusion of heat and momentum in numerically simulated convective clouds are investigated by means of a two-dimensional model. The numerical experiments include both variable and constant exchange coefficients, and the results are compared with those of experiments where diffusion is omitted altogether. The comparison shows that without eddy diffusion the simulated cloud development is unrealistically intense. In contrast, both types of simulated eddy diffusion prevent excessive developments and produce clouds whose overall features are similar to those of observed clouds. Of the two types of parameterized diffusion, the one whose eddy exchange coefficient is variable appears to give the best results. This is reflected in a more realistic initial stage of cloud development and stronger turbulent entrainment near cloud boundaries in agreement with observations.