Entrainment in Cumulus Clouds

Entrainment of dry air into cumulus clouds influences the development of the clouds in a major way. The many aspects of the entrainment process are examined in this paper by critically reviewing the literature from the time when investigations began. It is an interesting time in the evolution of the study of cumulus clouds with the advent of different models and several new instruments. Traditional entraining plume and thermal models that received considerable attention during the early years are being replaced by episodic-type mixing models. Recent observations of the source of entrained air are in part responsible for the new thinking, but the ideas really originate with the suggestion made by Squires more than 40 years age that vertical rather than horizontal mixing causes the dilution of cumuli by the process of penetrative downdrafts.