Scale Selection in Locally Forced Convective Fields and the Initiation of Deep Cumulus

Abstract
Deep cumulus dynamics has often been treated as an initial value problem where the long time effect of surface energy fluxes are neglected. Initiation is often assumed to follow from a strong localized deformation of the flow field, which is elsewhere quiescent. In nature, however, the atmosphere is rarely found in an undisturbed condition just prior to the inception of deep growth. One likely cause of widespread motions is the natural modal response of the environment to surface energy fluxes which results in a field of disturbances. 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 term 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 clou... Abstract Deep cumulus dynamics has often been treated as an initial value problem where the long time effect of surface energy fluxes are neglected. Initiation is often assumed to follow from a strong localized deformation of the flow field, which is elsewhere quiescent. In nature, however, the atmosphere is rarely found in an undisturbed condition just prior to the inception of deep growth. One likely cause of widespread motions is the natural modal response of the environment to surface energy fluxes which results in a field of disturbances. 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 term 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 clou...