Entrainment and the Temporal Development of the Microphysies of Convective Clouds

Abstract

This paper addresses the question of time changes in the cloud parcels comprising a cumulus cloud. Observations are analyzed which show how a cloud parcel begins its life on the upshear side of the cloud. As the cloud as a whole continues to develop upshear, the particular parcel is diluted by entrainment of dry air from above it, and the vertical cycling of cooled parcels formed in this way produces complex modifications of the cloud droplet spectra which can be traced in the observations. As this process continues, the parcel is found closer and closer to the downshear evaporating side of the cloud as the parcel is modified and ages. When sufficiently diluted, the whole cloud column subsides and evaporates. The largest cloud drops, and the ice particles, are found in the older, diluted, decaying side of the cloud.