Collaborative Research: RAPID--The Influence of Terrain on Tornado Characteristics Following the 10-11 December 2021 Tornado Outbreak

最近关于地形对龙卷风影响的观测和模拟研究普遍指出需要进一步研究。2021年12月10日至11日的龙卷风爆发提供了一个独特而宝贵的机会，通过对经过复杂地形的强龙卷风破坏的森林地区进行空中和地面评估，填补了知识空白。这个快速反应研究（Rapid）项目的主要目标是提供地形对龙卷风特征影响的初步评估。项目团队将根据航空图像和地面调查对森林破坏和地形进行高分辨率评估，然后使用GIS工具、机器学习和分析涡旋模型，对不同地形特征的破坏水平和龙卷风特征进行定量比较。结果将为简单的工程模型提供信息，以评估对建筑和自然环境的风险，并将在公众可能不认识到危险的地区提高对龙卷风威胁的普遍认识。现有的地形对龙卷风特征影响的研究存在很大的局限性，包括案例研究数量有限，模拟参数理想化，结果不确定或相互矛盾。一种新的研究方法将测试以下假设：1)龙卷风强度随着涡旋上坡（下坡）而减小（增大）；2)地表粗糙度越大（越低）导致近地表风越强（越弱）；3)地形特征可以以可预测的方式改变龙卷风的路径。该方法采用运动结构（SfM）摄影测量距离成像技术，通过开发二维正形图和三维点云，包括数十万棵树的大小、位置和配置信息，在厘米尺度上提供极高分辨率的地形和树木特征。这里收集的数据和随后的分析将有助于气象和工程界就地形对龙卷风环流的影响达成科学共识，并将允许进行新的和更详细的研究。虽然大涡模拟（LES）测试超出了工作范围，但这里收集的数据也将使下一代LES研究具有比以前更大的现实性。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。

Recent observational and modeling studies of the influence of terrain on tornadoes have universally cited the need for further research. The 10-11 December 2021 tornado outbreak provides a unique and valuable opportunity to fill knowledge gaps by conducting both aerial and ground evaluations in forested areas damaged by strong tornadoes that passed over complex terrain. The primary objective of this Rapid Response Research (RAPID) project is to provide a preliminary evaluation of the influence of terrain on tornado characteristics. The project team will conduct a high-resolution assessment of forest damage and terrain based on aerial imagery and ground surveys, and then develop a quantitative comparison of damage levels and tornado characteristics across terrain features using GIS tools, machine learning, and analytical vortex models. Results will inform simple engineering models to assess risk to the built and natural environment and will enhance general awareness of the threat of tornadoes in areas where the public may not recognize the dangers. Existing research into the influence of terrain on tornado characteristics has substantial limitations, including a limited number of case studies, idealized simulation parameters, and inconclusive or contradictory results. A novel research approach will test the hypotheses that 1) tornado intensity decreases (increases) as the vortex moves uphill (downhill), 2) higher (lower) surface roughness leads to stronger (weaker) near-surface winds, and 3) terrain features can deflect the path of a tornado in predictable ways. This approach employs the structure-from-motion (SfM) photogrammetric range imaging technique to provide an extremely high-resolution characterization of both terrain and treefall at centimeter scales through the development of 2-D orthomosaics and 3-D point clouds that include information on the size, location, and disposition of hundreds of thousands of trees. The data collected here and the subsequent analyses will help the meteorological and engineering communities to move toward scientific consensus regarding the influence of terrain on tornadic circulations and will allow for new and more detailed research studies. Although large eddy simulation (LES) tests are beyond the scope of the work, the data collected here will also enable next-generation LES studies with far greater realism than has previously been possible.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.