Numerical and Observational Studies of UTLS Potential Vorticity Dipoles in Midlatitude and Tropical Cyclones

中纬度气旋（MC）和热带气旋（TC）是对社会产生重大影响的主要风暴。它们复杂的演变过程受对流层上部和平流层下部大气中尺度运动的影响。研究人员发现，这些气旋内的强对流上升气流可以在UTLS中诱导反向旋转的空气循环，称为位涡（PV）偶极子。在风暴顶部附近，这些偶极子产生水平气流增强（或“小喷流”）和强烈扰动，可以显著改变风暴的演变和降水量。本研究旨在探讨这些ULTS功能相关的MC和TC。新出现的结果可以提高我们预测大风暴的能力，有助于尽量减少其影响。特别是PV偶极子的负异常是惯性不稳定的，可以促进降水和改变中尺度和天气系统的演变。再加上偶极子的方向，射流似乎形成的结果，在水平速度的差异，在上升气流相比，周围的UTLS空气。研究人员假设，在MC中，射流将与环境流相反，负PV异常位于流的左侧。而在TC中，小射流将与低对流层气旋流的意义相同，惯性不稳定成员径向向外。为了验证这一假设，该提案将对广泛的MC和TC案例中UTLS中的PV偶极子进行数值和观测研究，并将探索它们的动力学，发生以及与恶劣天气的关系。调查将集中在四个相互关联的领域：（1）PV偶极子的动力学，（2）PV偶极子的气候学方面，（3）UTLS PV和上中西部的极端洪水事件，以及（4）中尺度数值模拟中PV偶极子与辅助观测的比较。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准。

Midlatitude cyclones (MCs) and tropical cyclones (TCs) account for the major storms that greatly impact society. Their complex evolution can be influenced by atmospheric mesoscale motion in the upper troposphere and lower stratosphere (UTLS). The investigator has found that strong convective updraft within these cyclones can induce counter rotating air circulations, known as potential vorticity (PV) dipoles, in the UTLS. Near the top of the storms, these dipoles create horizontal flow enhancement (or "jetlets") and strong perturbations that can significantly modify the storm evolution and precipitation amount. This study aims to examine these ULTS features related to MCs and TCs. Emerging results can improve our ability to forecast major storms, helping to minimize their impacts. In particular, the negative anomaly of the PV dipole is inertially unstable and can promote precipitation and alter the evolution of mesoscale and synoptic systems. Coupled to the dipole orientation, the jetlets appear to form as a result of the difference in horizontal speed in the updraft compared to that of the surrounding UTLS air. The investigator hypothesizes that, in MCs, the jetlet will oppose the ambient flow, with the negative PV anomaly lying to the left of the flow. While in TCs, the jetlet will be in the same sense as lower tropospheric cyclonic flow, with the inertially-unstable member lying radially outward. To test this hypothesis, the proposal will carry out numerical and observational studies of the PV dipoles in the UTLS for a wide range of MC and TC cases, and will explore their dynamics, occurrence, and relationship with severe weather. The investigation will focus on four linked areas: (1) dynamics of PV dipoles, (2) climatological aspects of PV dipoles, (3) UTLS PV and extreme flooding events in the Upper Midwest, and (4) comparison of PV dipoles in mesoscale numerical simulations with auxiliary observations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.