A Climatological and Forecast Perspective on the Lower Stratospheric Environment During Synoptic Waveguide Perturbation Events

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The troposphere is the domain of weather systems that affect people and conditions on the ground, while the stratosphere is home to more slowly varying and larger scale circulation features which lie above tropospheric weather. Yet there is increasing awareness that the circulation in the stratosphere can affect tropospheric weather, and a proper representation of the stratosphere is important for numerical models used in medium-range weather forecasting. Likewise, circulation disturbances in the troposphere are known to affect the stratosphere, but the established theory for this influence emphasizes large and slowly moving jet stream meanders known as planetary waves rather than the smaller and faster synoptic waves associated with frontal weather. But recent results suggest that certain kinds of synoptic disturbances can also affect the stratosphere. Research conducted under this award seeks to advance understanding of the mutual interaction between these synoptic disturbances and the stratospheric circulation. Three types of synoptic disturbances are investigated: blocking anticyclones (stationary high pressure systems which induce persistent weather conditions), explosive cyclogenesis (which is associated with severe winter snowstorms along the US eastern seaboard), and the extratropical transition of tropical cyclones (which occurs as hurricanes recurve out of the tropics and interact with the mid-latitude jet streams). All of these disturbances have been shown to have a far-field influence in the downstream direction, through their ability to perturb the waveguide associated with the jet streams. Previous research has also suggested connections to the stratosphere, for instance blocking anticyclones are associated with later sudden stratospheric warmings, and several well-known cases of explosive cyclogenesis (including the 1979 President's Day storm) were preceded by downward wave propagation from the stratosphere. The research will be conducted using objective criteria to identify specific instances of the three types of disturbances, and to subdivide these into cases in which the circumpolar stratospheric circulation is strengthening, strong, weakening, or weak. The analysis will be conducted both using reanalysis datasets and extended-range ensemble forecasts performed as part of the Stratospheric Network for the Assessment of Predictability (SNAP) experiments.The work has broader impacts due to the potential for improvement in weather forecast skill that can come from a better understanding of stratosphere-troposphere interactions accompanying synoptic disturbances that are associated with severe weather. The PI is directly engaged in SNAP, which has been organized to address issues known in the operational medium-range forecast communities. The PI will also create a webpage devoted to real-time diagnostics of stratosphere-troposphere interaction. The webpage will serve as an educational tool for use in real-time forecast discussions in a classroom setting. Beyond these broader impacts, the project supports a full-time PhD student and provide summertime support for an MS student, thereby promoting the next generation of scientists in this research area.