The Impact of Ambient Deep-Tropospheric Vertical Wind Shear on Tornadoes and Their Attendant Supercells within Tropical Cyclones

飓风和热带气旋登陆会产生许多危险，从风力破坏到洪水再到风暴潮。本项目将研究热带气旋登陆、龙卷风的一个较少被研究的方面，特别是风切变在其发展中的作用。热带气旋引发的龙卷风通常比超级单体龙卷风弱，但它们对公共安全构成威胁。热带气旋的强度与龙卷风的数量之间没有直接的联系，预报指南通常是通用的。该奖项将提供对热带气旋龙卷风的基于研究的理解，这将使天气预报员能够更好地提醒公众这些危害。该项目还将涉及多名学生，作为下一代研究人员的培训。研究小组计划分析和模拟热带气旋登陆时垂直风切变对龙卷风发生的作用。龙卷风经常在飓风登陆时发生，但在其他强度相似的热带气旋中，龙卷风的数量可能会有一个数量级的变化。这些龙卷风也比更常见的大平原龙卷风更难预测。本研究将利用再分析资料、雷达资料和大气探测资料等对对流层深处垂直风切变和热带气旋相对螺旋度的观测分析，以及基于wrf的预报预警系统（WOFS）的模拟，以：1)利用其他相关因子（如日循环）检验龙卷风与热带气旋深层对流和垂直风切变之间关系的变异性；2)评估龙卷风超级单体可预测性对垂直风切变的敏感性；3)利用观测资料和由后预报计算的拉格朗日垂直涡度平衡，确定垂直风切变如何为热带气旋龙卷风超级单体创造有利环境。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Hurricane and tropical cyclone landfalls produce numerous hazards, from wind damage to flooding to storm surge. This project will address a lesser-studied aspect of tropical cyclone landfalls, tornadoes, and specifically the role of wind shear on their development. Tropical cyclone induced tornadoes are generally weaker than supercell tornadoes, but they are a public safety hazard. There is not a direct correlation between the strength of a tropical cyclone and the resulting number of tornadoes and forecast guidance is often generic. This award will provide a research-based understanding of tropical cyclone tornadoes which should allow operational weather forecasters to better alert the public of these hazards. The project will also involve multiple students as training for the next generation of researchers.The research team plans an analysis and modeling study of the role of vertical wind shear on the occurrence of tornadoes in landfalling tropical cyclones. Tornadoes frequently occur during hurricane landfall, but the number can vary by an order of magnitude among tropical cyclones that are otherwise of similar strength. These tornadoes are also much less predictable than the more common Great Plains tornadoes. This study will use observational analysis of the deep-tropospheric vertical wind shear and tropical cyclone-relative helicity from reanalysis data, other observations such as radar data and atmospheric soundings, and modeling with the WRF-based Warn on Forecast System (WOFS) to: 1) Test the variability of the relationship between tornadoes and deep convection in tropical cyclones and vertical wind shear with other relevant factors (e.g. diurnal cycle), 2) Assess the sensitivity of tornadic supercell predictability to vertical wind shear in hindcasts, and 3) Identify how vertical wind shear creates favorable environments for tropical cyclone tornadic supercells using observations and Lagrangian vertical vorticity budgets computed from hindcasts.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.