The Role of Convectively Generated Rear-Inflow Jets in the Evolution of Long-Lived Mesoconvective Systems

Abstract

In this study, the structure of convectively generated rear-inflow jets and their role in the evolution of long-lived mesoconvective systems are investigated through an analysis of idealized three-dimensional simulations using a nonhydrostatic cloud model. Rear-inflow jets are generated within these systems in response to the upshear-tilting of the convective circulation, as the horizontal buoyancy gradients along the back edge of the expanding system create a circulation that draws midlevel air in from the rear. Within this framework, a wide range of rear-inflow strengths and structures are produced, depending on the magnitude of the ambient convective available potential energy (CAPE) and the vertical wind shear. In general, for environments characterized by weak-to-moderate vertical wind shear and weak-to moderate CAPE, the rear-inflow jet descends and spreads along the surface well behind the leading edge of the gust front, and the subsequent convective activity becomes weaker. However, for environments characterized by strong environmental vertical wind shear and strong CAPE, the rear inflow remains elevated to near the leading edge of the system, and strong, upright convective cells are maintained along the gust front. The influence of the rear-inflow jets on the evolution of these systems is examined through an extension of the recent theory of Rotunno et al., whereby the characteristics of the lifting produced at the leading edge of the system are controlled by the relative balance between the horizontal vorticity generated by the cold pool and the horizontal vorticity that is inherent in both the ambient vertical wind shear and the rear-inflow jet.