An Observational Analysis of Entrainment in Deep Convection

Abstract

A critical factor affecting overshooting tops in deep convection is the entrainment of dry free tropospheric air, which reduces updraft magnitudes and may reduce the overall storm depth. The goal of this work is to improve our understanding of the environmental factors controlling entrainment using a large data set of observed thunderstorms. We accomplish this by investigating the estimated radar‐observed level of neutral buoyancy (LNB), that is, the level of maximum detrainment (LMD), to the LNB predicted for an undiluted parcel, tropopause height, and other environmental parameters from reanalysis data over the central and eastern United States during May‐August of 2021–2022. Specifically, we consider how variability in storm modes, environments, and months might impact the magnitude of convective effective entrainment. Overall, we find that effective entrainment is lowest in environments with stronger lower tropospheric shear, a drier 2–6 km layer, higher lifted condensation level, lower most unstable convective available potential energy (MUCAPE), and higher entraining CAPE (ECAPE)/MUCAPE ratio. In particular, LMD is closer to both the LNB and tropopause within stronger lower tropospheric shear and higher ECAPE/MUCAPE ratio environments, such that these storms have greater tropopause‐overshooting potential. This work presents the first systematic evaluation over the mid‐latitudes of how parcel theory predicts storm depth over a large sample of storms and provides valuable insight into factors that impact effective entrainment. These results can be used to inform our understanding of the relationship between convective environments, the resulting storms, and the potential of those storms to reach the stratosphere.