Constraining the Quantity of Tropospheric Air Irreversibly Transported to the Lower Stratosphere via Tropopause-Penetrating Convection with In Situ Observations

There is increasing observational evidence of the convective penetration of the lower stratosphere at mid-latitudes, particularly in the summertime North American and Asian Monsoon regions. It is theorized that gravity wave breaking and turbulent mixing associated with this tropopause-penetrating convection leads to the irreversible deposition of water as ice in the stratosphere, which then rapidly sublimates in the undersaturated environment. Tropopause-penetrating convection may also deliver tropospheric air directly to the overworld stratosphere, with further implications for the chemical composition of this region. In the present analysis we utilize a mix of simultaneously obtained in situ measurements of long-lived trace species to constrain the quantity of tropospheric air that is transported via convection. The trace species considered include CO, CH₄, CO₂ and O₃, and were acquired aboard NASA's ER-2 in encounters with convectively sourced plumes the Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) mission. A simple mixing model is used to constrain contributions from multiple source regions for air in the lower stratosphere over the U.S. in summer, including the contribution from tropopause-penetrating convection. Preliminary results from the largest outflow plume sampled during SEAC4RS do not show evidence for a large influx of tropospheric air, even where water vapor is significantly elevated. Instead, the data show evidence for convectively induced vertical "down mixing" of older stratospheric air into the plume regions, which is consistent with gravity wave breaking and the associated vertical overturning of isentropes.