Simulated Impacts of Tropopause-Overshooting Convection on the Chemical Composition of the Upper Troposphere and Lower Stratosphere

Tropopause-overshooting convection transports air from the lower troposphere to the upper troposphere and lower stratosphere (UTLS) where the resulting chemistry and mixing of trace gases can modify the radiation budget. While recent work has examined output from model simulations as well as aircraft and satellite observations of the impacts of tropopause-overshooting convection on UTLS composition, the range of potential impacts and their dependence on characteristics of storms and their environments is not known. Here, two 10-day periods, one representative of springtime convection and one representative of summertime convection, were simulated with the Weather Research and Forecasting (WRF) model with Chemistry to examine the range of UTLS composition impacts from tropopause-overshooting convection. Overall, springtime convection has a larger impact on UTLS composition than summertime convection, with a net effect of increasing water vapor (H2O) in the lower stratosphere and increasing ozone (O-3) in the upper troposphere. Springtime convection frequently increases the domain average H2O mixing ratio in the lowermost stratosphere by over 20% while changes in stratospheric H2O from summertime convection are much lower (similar to 7%-11% increase), reflecting a dependence of the maximum possible H2O increase on UTLS temperature. Increases in upper troposphere O-3 mixing ratios span the range 8%-19% from springtime convection and are minimal from summertime convection. Changes in the composition of the UTLS from tropopause-overshooting convection are largely dependent on the height and temperature of the tropopause, with the largest changes being in environments with relatively low tropopause heights between 11 and 13 km (typical of springtime environments in the United States).

Automated summary

The study found that the impacts of tropopause-overshooting convection on UTLS composition depend on storm and environmental characteristics, with springtime convection having a larger impact on UTLS composition compared to summertime convection. The main effects include an increase in water vapor and ozone mixing ratios, particularly in the lower stratosphere and upper troposphere.