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

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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.