FIELD VERIFICATION OF THE RELATIONSHIP BETWEEN ENTRAINMENT RATE AND CUMULUS CLOUD DIAMETER.

Abstract

A study has been conducted with the aim to verify an expression which relates the entrainment rate in a cumulus cloud to the diameter of that cloud, where the entrainment rate is defined as the fractional increase in cloud mass due to mixing with the environment, per unit height. A series of airplane penetrations of relatively small cumulus clouds, conducted during the summer of 1971, was used as a data base for making entrainment calculations. When a stratification of 23 cloud passes was analyzed, a strong inverse diameter dependence on the mixing rate was evident. For six cloud passes that were described as vigorously growing, well-defined, single isolated towers, the inverse relation was even stronger. There was a strong indication that the cumulus clouds studied were best described as the end result of an evolution of a series of starting plumes, rather than as purely plume or bubble elements.