Scale selection in locally forced convective fields and the initiation of deep cumulus

Abstract

Evidence is presented in this paper for the possible existence of a class of solutions when deep convection is allowed to evolve in the context of a thermally forced field of shallow convection. This class of solutions is neglected when one visualizes the growth of severe local storms in terms of buoyant bubbles in an otherwise tranquil atmosphere. Considering deep cumulus initiation as a field problem severely limits the concept of an isolated cloud. Individual clouds may owe much of their structure to the existence of, and interaction with, the field of thermally forced deep normal modes. The importance of the local forcing terms is demonstrated here through a numerical simulation of the evolution of deep and severe convection out of a locally forced shallow cloud field in the absence of large scale forcing. Finally, the interaction of a moving storm system in its severe stage with the boundary-layer modes appears to provide one explanation for the spatial and temporal distribution of new convective cells in a multicellular storm system. -from Authors