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

在美国，破坏性的雷暴事件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科事件是美国历史上损失最惨重的雷暴事件，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，雷暴风还没有得到气象学家和工程师的充分研究。这个灾害恢复研究资助（DRRG）项目将研究雷暴风的特征，包括设计级别的峰值风速，如何与雷暴风的不同产生机制相关联。该项目还将调查与这些机制有关的空间变异性和时间间断性，这将有助于对雷暴-风的产生和实地观测到的变异性的基本了解。该项目对危险雷暴的潜在关注最终将有助于更好地预测和预警雷暴-风事件，并将研究结果纳入建筑规范和标准。此外，该项目将培养新一代的跨学科工程师和科学家，他们既能理解基本的科学问题，也能理解工程解决方案。概念上的风害模型，特别是工程上的风害模型，一直把重点放在“下爆”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）和中涡旋，它们可能对雷暴造成的很大一部分损害负责。根据数值模拟的早期结果，在2020年8月的derecho中怀疑是由rij引起的风。该项目将结合2020年8月derecho和其他高影响事件的现有观测数据，结合事件后的损害调查，以及待开发的对流风暴事件的高分辨率数值模拟，研究其他强迫机制。主要的研究任务有三个：(1)具体事件的数值模拟，具有足够的分辨率来确定风的产生机制和相关的强迫，以及简化的动力学模拟，将风的强迫与雷暴风的详细特征联系起来。(2)风工程分析，将具体事件的模拟结果与现有雷暴风数据和事件后损害数据进行匹配/比较，并对高分辨率数值模型生成的数据进行分析。该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，特别关注这些风的产生机制（RIJ、下暴、中涡旋）。将通过(2)中的工程特性评估每种机制在结构风荷载中的重要性。这将把(1)和(2)的结果联系起来。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。

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.