Dynamics of Nonactive Parts of Convective Clouds

Abstract

A model of the dynamically inactive parts of cumulus cloud (i.e., void of bulk, organized vertical drafts) is proposed. It is assumed that such parts of clouds consist of coarse filaments of saturated, droplet-containing air mixed with filaments of air free of liquid water and perhaps even unsaturated. During vertical motions saturated and unsaturated filaments change their buoyancy according to dry- and wet-adiabatic processes, respectively, but being entangled with each other, they cannot develop separate vertical drafts of reasonable scale; the latter can form only if bulk net buoyancy occurs. A preliminary study of evolution of such a mixture due to bulk vertical motion and internal homogenizing 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 unstable stratification. Some generalizations of these results and applications to real clouds are briefly discussed.