Upshear and downshear evolution of cloud structure and spectral properties

A dynamical model, in conjunction with a microphysical model designed to predict evolution of cloud droplet spectra, is employed to perform two-dimensional simulations of a small nonprecipitating cumulus cloud in the presence of wind shear. Upshear-downshear differences in terms of entrainment sites, mixing zones, degree of dilution, and spectral properties are investigated and compared to some observations. Results show no systematic differences between the upshear and downshear sides of individual cloud turrets composed of cloudy air of rather uniform age. However, important differences in the spectral properties are noted between new cloudy air growing on the upshear side of the cloud and older cloudy volumes dissipating on the downshear side of the cloud. It is found that stronger wind shear inhibits the interaction between cloud turrets of different ages.