Tropopause‐overshooting convection in the midlatitudes rapidly transports lower troposphere air and cloud material to the upper troposphere and lower stratosphere (UTLS), with notable events resulting in the formation of above‐anvil cirrus plumes (AACPs). However, there is limited understanding of how transport driven by overshooting convection and AACP properties are modified by variations in UTLS environments, especially the extent of stratosphere‐to‐troposphere (i.e., downward) transport. Here, AACP development and UTLS transport sensitivities to lower stratosphere stability and the UTLS wind environment are evaluated. The Bryan Cloud Model is used to simulate midlatitude supercell convection and evaluate resulting UTLS composition changes within two common midlatitude thermodynamic environments: a single tropopause and a double tropopause, and two UTLS wind environments: one with a stronger stratospheric wind profile supportive of frequent gravity wave breaking and AACP development and the other with a weaker stratospheric wind profile to suppress gravity wave breaking and discourage AACP formation. Multiple passive tracers and water vapor concentrations are used to evaluate the exchange of air between the troposphere and stratosphere and transport confined to each layer. It is found that greater troposphere‐to‐stratosphere transport (TST) and stratospheric hydration occurs in storms with AACPs, while stratosphere‐to‐troposphere transport (STT) is greater in storms without AACPs. This STT is facilitated by a mechanical oscillation induced by the overshoot. AACP‐producing storms have increased downward transport of stratospheric overworld air to the lowermost stratosphere, which is enhanced within a double tropopause environment. More expansive AACPs, deeper overshoots, and greater TST also occurs in double tropopause environments.

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Tropopause Polar Vortices (TPVs) are coherent circulations that occur over polar regions and can be identified by a local minimum in potential temperature and local maximum in potential vorticity. Numerous studies have focused on TPVs in the Arctic region, however, no previous studies have focused on the Antarctic. Given the role of TPVs in the Northern Hemisphere with surface cyclones and other extreme weather, and the role that surface cyclones can play on moisture transport and sea ice breakup, it is important to understand whether similar associations exist in the Southern Hemisphere. Here, characteristics of TPVs in the Antarctic are evaluated for the first time under the hypothesis that their characteristics do not significantly differ from those of the Northern Hemisphere. To improve understanding of Antarctic TPV characteristics, this study examines TPVs of the Southern Hemisphere and compares them to their Northern Hemisphere counterparts from 1979-2018 using ERA-Interim data. Common characteristics of TPVs including frequency, locations, lifetimes, strength, and seasonality are evaluated. Results indicate that topography correlates to the geographic distribution of TPVs and the locations of local maxima TPV occurrence, as observed in the Northern Hemisphere. Additionally, TPVs in the Southern Hemisphere exhibit seasonal variations for amplitude, lifetime, and minimum potential temperature. Southern Hemisphere TPVs share many similar characteristics to those observed in the Northern Hemisphere, including longer summer lifetimes.The association of Southern Hemisphere TPVs and surface cyclone frequency is explored, and it appears that TPVs have a precursory role to surface cyclones, as seen in the Northern Hemisphere.

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