DYNAMICS OF NONACTIVE PARTS OF CONVECTIVE CLOUDS

A model of the dynamically inactive parts of cumulus cloud (i.e., void of bulk, organized vertical drafts) is proposed. It is assumed that s uch parts of clouds consist of coarse filaments of saturated, droplet- containing air mixed with filaments of air free of liquid water and pe rhaps even unsaturated. During vertical motions saturated and unsatura ted filaments change their buoyancy according to dry- and wet-adiabati c processes, respectively, but being entangled with each other, they c annot develop separate vertical drafts of reasonable scale; the latter can form only if bulk net buoyancy occurs. A preliminary study of evo lution of such a mixture due to bulk vertical motion and internal homo genizing mixing (which both affect the latent sensible heat transition ) is made by means of a one-dimensional model. Results of a number of runs of the model are presented, confirming the supposition that cloud with such a structure can persist fairly long even in conditionally u nstable stratification. Some generalizations of these results and appl ications to real clouds are briefly discussed.