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 (NEXRAD) and the ERA5 reanalysis to locate OC during May–August of 2008 to 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.

The warm rain process is an important part of shallow cumulus convection and can influence both cloud microphysics and cloud radiative effects. Model studies suggest that as shallow cumulus grow in size, the likelihood of warm rain increases due to a decreasing impact of entrainment on cloud updrafts. This implies a reduction in evaporative effects near cloud center that may result in more efficient conversion from cloud water to precipitation as cloud size increases. While these findings have been illustrated with cloud resolving models, the likelihood of precipitation and the sensitivity of precipitation efficiency to cloud size has not yet been tested by global observations. A-Train satellite observations, with sensors sensitive to both cloud and precipitation water, can be used to examine shallow cumulus behavior with cloud size. We combine CloudSat and MODIS observations to create a warm cloud climatology by identifying warm oceanic contiguous cloud objects with top heights below the freezing level from August 2006 - December 2010. The characteristics of each cloud object, including cloud top height, along-track extent (size), vertical reflectivity gradients, integrated cloud and precipitation water, and column water vapor (CWV) environment, are calculated. As a proxy for warm rain efficiency, the ratio of precipitation to cloud water is also analyzed for varying cloud object sizes. For a fixed top height, our results show rain likelihood increases with cloud size. Our initial results support the hypothesis that as shallow cumulus size increases and/or environmental moisture increases, shallow cumulus updrafts are able to support larger droplets that are more likely to fall out as rain. Planned analysis will determine how our proxy for warm rain efficiency changes with cloud size.