Improving our Understanding of Cross-Tropopause Transport with Idealized Simulations of Convection

Overshooting convection has been shown to significantly alter the chemical makeup of the upper troposphere and lower stratosphere, ultimately impacting the Earth’s climate system. For instance, three-fold increases in water vapor concentrations within the stratospheric overworld (θ > 380 K) have been directly tied to overshooting convection. Significant enhancements in water and lower-tropospheric pollutants have also been observed recently at θ > 460 K (altitude > 19 km). However, observations are not sufficient for completely understanding the three-dimensional structure of plumes originating from overshooting convection. Determining the full magnitude of the resulting stratospheric hydration remains a challenge due to the rapid spatiotemporal evolution typical of convective environments and the inability to safely sample updrafts in situ with aircraft instrumentation.

To fill this gap and improve our understanding of the three-dimensional characteristics of these plumes of boundary layer air detrained above the tropopause, high-resolution simulations using the CM1 idealized cloud model will be presented for a supercell and non-supercell case. Because supercells tend to be the strongest storms with the most robust, entrainment-resilient updrafts, it is hypothesized that they produce deeper overshoots with more air originating near the surface being detrained farther into the stratosphere. The goal of this work was to determine if, and to what extent, supercells have a greater impact on stratospheric chemistry. To help answer this, the maximum altitudes influenced by convective transport were determined for each case using passive tracers and forward trajectories initiated within both a near-surface layer and the overshooting tops of each storm. Furthermore, calculating what proportion of the trajectories immediately return to the troposphere versus remaining in the stratosphere showed how much updraft air was irreversibly transported above the tropopause. Lastly, the magnitudes of tracer and water vapor concentrations showed the amount of transport for each storm type, with water vapor budgets evaluated for parcels originating in the overshoots to reveal the relative contributions of various microphysical processes to stratospheric hydration.