With use of the model of the steady-state entraining cumulus draft, it is possible to describe the formation and structure of the downdraft observed at the down-shear edge of an oceanic trade-cumulus cloud. The observations are airplane traverses made at several levels giving the temperature, humidity, and vertical draft structure in cloud and environment, and a nearby pilot-balloon run. It is found that this downdraft must be mixing primarily with the updraft; that it gains its negative buoyancy mainly from evaporation; and that it is permitted to go through a life cycle of formation, strengthening, and decay which is closely dependent upon that of the updraft.
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Joanne Starr Malkus (1955) studied this question.