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

对流层是影响人类和地面条件的天气系统的领域，而平流层是对流层天气上方变化更慢、规模更大的环流特征的所在地。然而，人们越来越意识到，平流层中的环流会影响对流层天气，而对平流层的适当表示对于中期天气预报中使用的数值模式是重要的。同样，众所周知，对流层中的环流扰动会影响平流层，但这种影响的既定理论强调的是被称为行星波的大而缓慢移动的急流曲折，而不是与锋面天气相关的更小、更快的天气波。但最近的结果表明，某些类型的天气扰动也会影响平流层。根据该奖项开展的研究旨在增进对这些天气扰动和平流层环流之间相互作用的了解。研究了三种类型的天气扰动：阻塞反气旋(导致持续天气条件的静止高压系统)、爆发性气旋生成(与美国东海岸的严重冬季暴风雪有关)和热带气旋的温带转换(当飓风从热带回归并与中纬急流相互作用时发生)。所有这些扰动都已被证明在下游方向上具有远场影响，因为它们能够扰动与急流相关的波导。以前的研究也提出了与平流层的联系，例如，阻止反气旋与后来的平流层突然变暖有关，几个众所周知的爆炸性气旋发生案例(包括1979年总统日风暴)都是在平流层向下传播波。这项研究将使用客观标准来确定这三种扰动的具体情况，并将这些情况细分为绕极平流层环流增强、增强、减弱或减弱的情况。分析将使用再分析数据集和作为可预报性评估平流层网络(SNAP)实验的一部分进行的扩展范围集合预报。这项工作具有更广泛的影响，因为通过更好地了解与恶劣天气有关的天气扰动伴随的平流层-对流层相互作用，可以提高天气预报技能的潜力。PI直接参与SNAP，这是为了解决业务中期预报社区中已知的问题而组织的。PI还将创建一个网页，专门用于平流层-对流层相互作用的实时诊断。该网页将作为一种教育工具，用于课堂环境中的实时预报讨论。除了这些更广泛的影响外，该项目还支持一名全日制博士生，并为一名MS学生提供暑期支持，从而促进该研究领域的下一代科学家。

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.