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建模研究普遍认为需要进一步研究。2021年12月10日至11日龙卷风的爆发为填补知识空白提供了一个独特而宝贵的机会，方法是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。该快速反应研究(RAPID)项目的主要目标是初步评估地形对龙卷风特征的影响。项目组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，然后使用地理信息系统工具、机器学习和分析涡旋模型对各种地形特征的破坏程度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参考，以评估对建筑和自然环境的风险，并将在公众可能没有意识到危险的地区提高对龙卷风威胁的普遍认识。现有关于地形对龙卷风特征影响的研究有很大的局限性，包括有限的案例研究，理想化的模拟参数，以及不确定或矛盾的结果。一种新的研究方法将检验这样的假设：1)龙卷风强度随着涡旋向上(下坡)移动而减小(增加)，2)地表粗糙度越高(越低)，近地面风越强(越弱)，3)地形特征可以以可预测的方式偏离龙卷风的路径。该方法使用运动结构(SFM)摄影测量距离成像技术，通过开发2-D正射影像和3-D点云(包括有关数十万棵树的大小、位置和布置的信息)，提供厘米尺度的地形和树木瀑布的极高分辨率表征。这里收集的数据和随后的分析将有助于气象界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研究比以前更具现实性。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.