Transport and Confinement of Plumes From Tropopause-Overshooting Convection Over the Contiguous United States During the Warm Season

Tropopause-penetrating overshooting convection (OC) can transport tropospheric air into and affect the composition of the lower stratosphere. During the warm season, OC occurs frequently over the contiguous United States, and the transport of plumes from these events is modulated by the flow over North America, which throughout June to August is characterized by a large-scale anticyclone in the upper troposphere and lower stratosphere. This study uses data from the Next Generation Weather Radar and the ERA5 reanalysis to locate OC during May-August of 2008-2020. Evidence of convective transport is found well above the 380 K isentrope, which is the top of the lowermost stratosphere and also the top of the stratospheric middleworld. By initializing massless particles within the volume of OC above the tropopause, we perform trajectory calculations to simulate the transport of OC plumes. With three-dimensional diabatic trajectory modeling in isentropic coordinates using winds from ERA5, we quantify the confinement within the anticyclone and the number of trajectories transported into the tropical and extratropical stratosphere. By evaluating the trajectory residence time in the North American region, we find that July exhibits the strongest confinement, with about a quarter of trajectories staying in the region for more than 11 days. It is shown that, together with sufficient injection height, convective injection that occurs south of the jet and/or into anticyclonic regimes increases the chances of air remaining in the stratosphere. After 30 days, 45% of all air masses injected above the tropopause remain in the global stratosphere. Plain Language Summary Deep convection that reaches the tropopause, the boundary between the troposphere and stratosphere, can transport tropospheric air into the stratosphere. This type of transport is important because tropospheric air is rich in humidity and may contain anthropogenic emissions that can influence the composition and chemistry in the stratosphere. Deep convective events that penetrate the tropopause are common during summertime over the United States, and in this study we examine how air masses injected into the stratosphere by deep convection are transported over the global stratosphere. Results show that roughly a quarter of injected air masses may remain over North America for over 11 days, and after 30 days 45% of these air masses still remain in the global stratosphere.

Automated summary

Tropopause-penetrating overshooting convection can transport tropospheric air into the lower stratosphere and affect its composition. This study uses radar data and reanalysis to locate and simulate the transport of overshooting convection plumes over the United States. The results show that a significant number of air masses can remain in the stratosphere for extended periods, especially in July, and after 30 days, 45% of injected air masses still remain in the global stratosphere.