Gravity waves, compensating subsidence and detrainment around cumulus clouds

Abstract

The cloud develops a horizontally averaged density variation with height which is neutrally buoyant with respect to a moist adiabat. The buoyancy difference between the cloud and the undisturbed sounding produces circulations that can be understood as spreading gravity waves which adjust the environmental buoyancy to be equal to the cloud buoyancy by compensating subsidence. Unlike the circulations inside clouds, this adjustment takes place without turbulent mixing. Hence, the "buoyancy adjust time' T1 during which the environment comes into rough buoyant equilibrium with the clouds is much shorter than the "mixing time' T2 which it takes a tracer, initially concentrated at some level, to become homogenized through the layer in a field of clouds. -from Authors