A Persistent Regime of Organized Convection without a Mesoscale Downdraft

Theoretical models of the steady circulation of organized convection and squall lines have identified the important features that help maintain their overarching structure and longevity. These models, along with observations and simulations, have resulted in two common descriptions of organized mesoscale convective systems: the first regime is comprised of a front-to-rear jump updraft, an overturning updraft, and a well-developed rear-to-front downdraft circulation; and the second regime is similar to the first but without the overturning updraft branch. The theoretical models, however, identify another regime of organized convection that is comprised of jump and overturning updrafts but without a mesoscale downdraft circulation. This regime has received relatively little attention, presumably because these systems are less intense and do not contain a downdraft circulation that is normally thought to be a fundamental requirement for system longevity.

In this study we present a series of idealized model simulations of self-organizing convection that contain a persistent and robust regime of organized convection that does not have an established mesoscale downdraft circulation. The regime is comprised of well-defined jump and overturning updrafts, consistent with the regime identified by the theoretical models. Interestingly, despite its lack of downdraft circulation, the regime is shown to persist for tens of hours, undergoing periodic bursts of enhanced convective activity. In this presentation we will describe the structure and dynamics of this convective regime, explore its sensitivity to model configuration and environmental conditions, and describe its behaviour in two and three dimensions.