Detailed Examination of Upper Troposphere Lower Stratosphere Composition Change from In Situ Observations of Active Convection in the United States

Tropopause-overshooting convection in the midlatitudes provides a rapid transport pathway of air from the lower troposphere to the upper troposphere and lower stratosphere (UTLS), and can result in the formation of above-anvil cirrus plumes (AACPs).  Recent in situ observations from the Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) field campaign are used to examine impacts from active overshooting convection on UTLS composition. There are little to no prior airborne observations of active overshooting convection, making observations from this flight valuable to interpreting and exploring processes seen in idealized modeling studies. DCOTSS research flight 13 on May 31^st, 2022 sampled active overshooting convection over the state of Oklahoma for more than three hours with the NASA ER-2 high-altitude research aircraft. Additionally, an AACP was bisected during this flight, providing the first such extensive sampling of this phenomena. This study aims to provide a detailed understanding of changes in the UTLS composition from active overshooting convection and AACPs using the in-situ observations from this flight. The observations reveal multiple pronounced changes in air mass composition and stratospheric hydration. In agreement with prior modeling studies, maximum altitudes of water vapor enhancement were much higher than altitudes of mostly passive trace gas composition change. Stratospheric water vapor enhancements reached nearly a factor of four over background levels at a maximum altitude of 16.56 km and a potential temperature of 389.76 K. Carbon monoxide, a tracer of tropospheric origin, showed enhancements of a factor of two over background levels at a maximum altitude of 15.76 km and potential temperature of 363.6 K. There is a notable positive correlation between water vapor and ozone near the bisection of the AACP, which seems to be the result of horizontal mixing. It appears that the water vapor enhancement within the AACP was limited to the saturation mixing ratio of the low temperature environment.