AGS-PRF: Extreme Near-Surface Wind Speeds Associated with Coherent Small-Scale Vortices within the Boundary Layer of Tropical Cyclones

热带气旋拥有地球上任何地方都能发现的最强的近地面风，然而，强烈飓风特有的极端（80-100米/秒）本地风速产生的机制仍然知之甚少。初步研究表明，最强的风通常出现在强烈（10-25米/秒）上升气流附近，并与连贯的小尺度（1-3公里）涡旋有关。在这个项目中，这些强烈的上升气流及其相关涡旋的结构、动力学和影响将被研究。这将通过使用天气研究与预报模式（WRF）和布莱恩云模式（CM1）对真实数据和理想热带气旋进行高分辨率模拟分析来完成。将与先前由首席研究员收集的投下式探空仪观测数据集进行比较。最后，将利用Nolan的线性涡旋模型（3DVPAS）来确定这些涡旋是否是飓风眼壁边界层动力不稳定的结果。这些极端的上升气流（在4类和5类飓风中普遍存在）可能通过对边界层湍流混合、轴对称化和地表通量的影响，影响飓风的总体强度。因此，除了研究涡旋本身，该研究还将使用大涡模拟（LES）来确定这些特征可能（或可能不会）对风暴的更大尺度结构产生的影响。该项目将在NCAR进行，Richard Rotunno博士为赞助科学家，George Bryan博士为合作科学家。由于观测到登陆热带气旋时最严重的风害是高度局域化的，因此这些小尺度涡旋可能是造成这种情况的原因。因此，增加我们对这方面的理解是必要的，这个项目可以改进建模和更好地预测登陆时的地面风场。这些特征也对研究飞机构成了危险，因此正确理解遇到这些上升气流的风险将是有益的。因此，这项工作具有与热带气旋研究界、风力工程界和整个社会高度相关的潜力。

Intellectual meritTropical cyclones possess some of the strongest near-surface winds found anywhere on earth, yet the mechanisms by which the extreme (80-100 m/s) local wind speeds characteristic of intense hurricanes are produced remain poorly understood. Preliminary research has shown that the strongest winds are often found in close proximity to intense (10-25 m/s) updrafts and are associated with coherent small scale (1-3 km) vortices. In this project, the structure, dynamics, and impact of these intense updrafts and their associated vortices will be investigated. This will be accomplished through the analysis of high-resolution simulations of both real-data and idealized tropical cyclones, using the Weather Research and Forecasting Model (WRF) and the Bryan Cloud Model (CM1). Comparisons will be made to a dataset of dropsonde observations previously collected by the principal investigator. Finally, the linear vortex model of Nolan (3DVPAS) will be utilized to determine whether these vortices are a consequence of a dynamical instability of the boundary layer in hurricane eyewalls.These extreme updrafts (which are ubiquitous in category 4 and 5 hurricanes) might influence the overall intensity of hurricanes, through their effects on turbulent mixing in the boundary layer, axisymmetrization, and surface fluxes. Therefore, in addition to investigating the vortices themselves, the study will also use Large Eddy Simulations (LES) to determine the impact that these features may (or may not) have on the larger scale structure of the storm.This project will be undertaken at NCAR, with Dr. Richard Rotunno as the sponsoring scientist, and Dr. George Bryan as a collaborating scientist.Broader impacts As the most severe wind-damage in landfalling tropical cyclones has been observed to be highly localized, it is possible that these small-scale vortices are responsible for such occurrences. It is therefore imperative to increase our understanding in this respect, and this project could lead to improved modeling and better forecasts of the surface wind field at landfall. These features also pose a danger to research aircraft, and so a proper understanding of the risk of encountering these updrafts would be beneficial. Therefore, this work has the potential to be highly relevant to the tropical cyclone research community, to the wind engineering community, and to society at large.