Evaporation of rainfall below convective clouds

The purpose of this study is to obtain a better understanding of the evaporation process between cloud base and ground for areas with cloud bases greater than 1.6 kilometers. To accomplish this a parameterization method of sub-cloud evaporation was compared with a direct calculation method developed in this study. Test cases indicated that the direct method was the better method for calculating evaporation rates below relatively high convective cloud bases. The direct method was modified to consider the effects of time, sub-cloud vertical velocities, environmental modification and rainfall duration on the evaporation process. The model was then applied to several cases based on typical atmospheric conditions for West Texas in order to evaluate evaporation beneath convective clouds. It was found that thunderstorms that develop in relatively warm and dry air masses, thus having high cloud bases will suffer large depletions in liquid water between cloud base and ground. Furthermore, it was found that seeding convective clouds in order to enhance rainfall may produce up to four times the amount of rainfall at the surface than that which would fall from the same storms with naturally occurring rainfall rates. It appeared that seeding clouds with the lowest possible bases would be the most beneficial.