Parameterization of Trade-Cumulus Cloud Amounts

Abstract

Abstract A scheme for parameterizing the fractional cloud coverage of trade cumuli is developed which gives the cloud cover in terms of the cloud-layer relative humidity and the liquid water content of the convective elements. This parameterization gives good agreement with cloud observations obtained during the Atlantic Trade-Wind Experiment, 1969. The scheme was incorporated into a simple one-dimensional model of the thermodynamic structure of the trade-wind boundary layer in order to evaluate the dependence of cloud cover on sea surface temperature, surface wind speed, and radiative processes. For steady-state conditions over relatively cold water (∼16°C), the cloud cover decreases as sea surface temperature increases while over warmer water (∼24°C) there is a slight increase in cloud cover as the sea surface temperature increases. When used in a downstream mode, the model structure obtained by moving from cold to warm water can be used to evaluate the effect of advection. Over cold water, the advectiv...