Forcings, Characteristics, and Loadings of Damaging Winds in Derechos and Other High-Impact Thunderstorm Events

在美国，破坏性雷暴事件的数量比龙卷风多一个数量级，累积损失更大。最值得注意的是，2020年8月发生在美国中西部的德雷克事件是美国历史上损失最大的雷暴事件，损失超过130亿美元。关于这种极端风的产生机制的关键问题仍然没有得到回答，部分原因是相对于龙卷风，雷暴风一直没有得到气象学家和工程师的充分研究。这项抗灾研究补助金(DRRG)项目将研究雷暴风的特征，包括设计水平的最大风速，与这些风的不同生成机制有何关系。该项目还将调查与这些机制有关的空间变异性和时间间歇性，这将有助于从根本上理解雷暴-风的产生和实地观测到的变异性。该项目的基本重点是危险雷暴，最终将导致对雷暴事件的更好预报和警告，并将调查结果纳入建筑规范和标准。此外，该项目还将培养新一代跨学科的工程师和科学家，他们既了解基本的科学问题，也了解工程解决方案。概念性的风灾模型，特别是工程上的风灾模型，将重点放在“下暴流”上，因为它要对地表附近的所有极端风负责。然而，雷暴风的产生还有其他机制，包括后向流入急流(Rij)和中层涡旋，这可能是雷暴造成的相当大比例的损害。根据数值模拟的早期结果，人们怀疑2020年8月的德雷克事件中存在RIJ诱导的风。该项目将结合2020年8月德雷克和其他高影响事件的现有观测数据、事件后损害调查和即将开发的对流风暴事件的高分辨率数值模拟，审查替代强迫机制。三个主要的研究任务将梳理出不同的机制：(1)对特定事件的数值模拟，其分辨率足以确定风的生成机制和相关的强迫，以及降低复杂性的动力学模拟，以将风强迫与雷暴风的详细特征联系起来。(2)风工程分析，将特定事件的模拟结果与现有的雷暴风场数据和灾后破坏数据进行匹配/比较，以及对更高分辨率的数值模式产生的数据进行分析。这项分析将包括对工程相关特征的四维评估，如峰值风速、风速剖面，以及与现有雷暴风工程模型的比较。(3)美国雷暴风的气候学分析，特别关注按其生成机制(RIJ、下击暴流、中层涡旋)对这些风进行细分。将通过(2)中的工程特性来评估每种机制在结构风荷载中的重要性。这将把(1)和(2)的结果联系起来。这一奖项反映了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进行评估，被认为值得支持。

Damaging thunderstorm-wind events in the US outnumber those of tornadoes by an order of magnitude, with greater cumulative losses. Most notably, the August 2020 derecho event in the Midwest US was the costliest thunderstorm event in US history at over $13Billion in losses. Critical questions regarding the mechanisms for such extreme wind generation remain unanswered, partly because, relative to tornadoes, thunderstorm winds have been understudied both by meteorologists and engineers. This Disaster Resilience Research Grants (DRRG) project will examine how characteristics of thunderstorm winds, including design-level peak wind speeds, relate to the different generating mechanisms of such winds. The project will also investigate spatial variabilities and temporal intermittencies associated with these mechanisms, which will contribute to the fundamental understanding of thunderstorm-wind generation and the variability observed in the field. The underlying focus of the project on hazardous thunderstorms will ultimately lead to better forecasts and warnings of thunderstorm-wind events, and to integration of the findings into building codes and standards. In addition, the project will train a new generation of interdisciplinary engineers and scientists who appreciate both the basic scientific problem, and the engineering solutions.Conceptual wind-damage models, especially for engineering, have focused on the “downburst” as being responsible for all extreme winds near the surface. However, there are other mechanisms for thunderstorm wind generation including the rear-inflow jet (RIJ) and mesovortices, which may be responsible for a significant proportion of damage from thunderstorms. RIJ-induced winds are suspected in the August 2020 derecho based on early results from numerical simulations. This project will examine alternative forcing mechanisms by combining existing observational data from the August 2020 derecho and other high-impact events, with post-event damage surveys, and to-be-developed high-resolution numerical simulations of convective-storm events. Three major research tasks will tease out the different mechanisms: (1) Numerical simulations of specific events, with resolution sufficient for determination of the wind-generation mechanism and associated forcings and reduced-complexity dynamical modeling to relate the wind forcings to the detailed characteristics of the thunderstorm winds. (2) Wind engineering analysis, which will match/compare the modeling results of specific events to existing thunderstorm wind data and post-event damage data as well as an analysis of the data generated from the higher resolution numerical models. This analysis will include four-dimensional assessment of engineering-relevant characteristics such as peak wind speed, wind speed profiles, and comparisons to existing engineering models of thunderstorm winds. (3) Climatological analysis of thunderstorm winds in the US, with specific interest in sub-classifying these winds by their generation mechanism (RIJ, downburst, mesovortex). Each mechanism will be assessed for their importance in wind loading of structures through the engineering characteristics in (2). This will connect the results from (1) and (2).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.