Evaluating the Impacts of Storm-Scale and Environmental Factors on Stratosphere-Troposphere Exchange Associated with Midlatitude Convection

Abstract

Stratosphere-troposphere exchange (STE) plays a crucial role in Earth’s climate; however, the significance of small-scale processes such as deep midlatitude convection to global STE remains understudied relative to large-scale processes. Tropopause-overshooting convection in the extratropics is especially important for stratospheric water vapor because the radiative forcing sensitivity of water vapor is greatest there. Thus, it is essential to understand what factors influence the strength and prevalence of overshooting storms and associated STE. The U.S.\ Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) field campaign during 2021 and 2022 was the first large-scale airborne project for which sampling stratospheric impacts from overshooting convection was a primary focus. Our research utilizes the extensive DCOTSS dataset in combination with radar, satellite, and environmental observations to investigate the relationships between observed lower stratosphere composition change and various storm and environmental characteristics. We use back trajectories to link aircraft observations to observed storms and environments. Our results demonstrate greater magnitudes of troposphere-to-stratosphere transport for above-anvil cirrus plume (AACP)-producing storms and mesoscale convective systems (MCSs). In addition, the most extreme enhancements in water vapor and other tropospheric gases occur where the tropopause height is low and the depth of overshooting is high, especially for AACP-producing storms. These results provide new insights into types of storms and environments that generate the greatest stratopsheric impact. We also investigate the impact of storm and environmental characteristics on pathways for hydration (air mass transport and mixing versus ice sublimation), finding that they also modulate the frequencies of each process at different altitudes. Namely, mixing is found to be most prevalent in AACP-producing storms and MCSs, which can help explain transport differences between water vapor and other gases.