Stratocumulus cloud deepening through entrainment

Abstract

It is shown that under a fairly wide range of realistic conditions, stratocumulus cloud-top entrainment actually tends to deepen an existing cloud layer, or tends to produce clouds in an unsaturated mixed layer, even though the entrained air is warmer and drier than the mixedlayer air. These results do not depend on any particular theory of what determines the entrainment rate; they imply that the cloud-top entrainment instability discussed by Randall and Deardorff does not necessarily tend to destroy a layer cloud; it sometimes only makes the cloud deepen. Examples are presented, using the representative soundings of McClatchey et al., the marine-layer data of Neiburger et al., and results from a simulation produced with the UCLA general circulation model.