Convective influences on the upper troposphere and lower stratosphere over North America

2023.09.06 14:00-16:00



中國文化大學 大氣科學系

Convective storms not only modulate the tropospheric circulation but also exert a strong influence on the chemical composition and the circulation of the lower stratosphere. Storms that are especially strong can overshoot the tropopause and inject chemical species of tropospheric origin into the stratosphere. Aside from directly transporting air into the stratosphere, convection can also modulate circulation in the lower stratosphere through forced planetary waves. This talk gives an overview on the impacts of convection on the stratosphere, with a focus on the North American (NA) region. Preliminary results of the NASA Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) campaign show the strong hydrating effect of tropopause-overshooting convection (OC) on the lower stratosphere; we directly sampled convectively-influenced air with water vapor mixing ratio up to seven times the stratospheric background. Analysis based on weather radar data and air trajectory modeling suggests that almost half (45%) of air plumes originating from OC events remain in the stratosphere after thirty days, demonstrating the importance of OC over the U.S. on the global stratosphere. Injected air masses are often confined by an upper-tropospheric anticyclone over NA, and thus we are also interested in the dynamics of the anticyclone. We investigate the relationship between the anticyclone and precipitation in the North American Monsoon, and find that increased monsoonal precipitation is associated with a zonally-expanded anticyclone size, with the expansion being more notable towards the west.