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

在美国，破坏性的雷暴大风事件比龙卷风事件多一个数量级，累积损失更大。最值得注意的是，2020年8月在美国中西部发生的derecho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。关于这种极端风力产生机制的关键问题仍然没有答案，部分原因是，相对于龙卷风，气象学家和工程师对雷暴风的研究还不够。这个抗灾能力研究赠款（DRRG）项目将研究雷暴风的特征，包括设计水平的峰值风速，与这种风的不同产生机制的关系。该项目还将调查与这些机制有关的空间变异性和时间变异性，这将有助于从根本上了解雷暴风的产生和实地观察到的变异性。该项目的基本重点是危险的雷暴，最终将导致更好地预报和预警雷暴大风事件，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，他们既重视基本的科学问题，又重视工程解决方案。概念性风害模型，特别是工程模型，都把重点放在“下击暴流”上，认为它是造成地表附近所有极端风的原因。然而，雷暴风的产生还有其他机制，包括后入流急流（RIJ）和中涡，这可能是雷暴造成的很大一部分损失的原因。根据数值模拟的早期结果，在2020年8月的derecho中怀疑RIJ引起的风。 该项目将通过将2020年8月derecho和其他高影响事件的现有观测数据与事件后的损害调查以及即将开发的对流风暴事件的高分辨率数值模拟相结合，来研究替代强迫机制。三项主要研究任务将梳理不同的机制：（1）特定事件的数值模拟，具有足够的分辨率来确定风力发电机制和相关的强迫，并降低复杂性的动力学建模，以将风力强迫与详细特征联系起来。雷暴风。(2)风工程分析，将特定事件的建模结果与现有雷暴风数据和事件后损害数据进行匹配/比较，并分析从更高分辨率数值模型生成的数据。该分析将包括对工程相关特性的四维评估，例如峰值风速、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，特别关注这些风的生成机制（RIJ，下击暴流，中涡旋）的细分。通过（2）中的工程特性，评估每种机制在结构风荷载中的重要性。这将连接（1）和（2）的结果。该奖项反映了NSF的法定使命，并已被认为是值得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的支持。

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.