Investigation of the Impact of Terrain and Buildings on Tornado Dynamics Using High-Resolution Simulations

Terrain effects on tornadogenesis or tornado dynamics have been hypothesized for several decades, often based on evidence from damage surveys. To date, these effects have not been robustly quantified using numerical simulations and the physical mechanisms responsible for terrain-induced changes in tornado wind speeds have not been deeply explored. For example, it remains unclear if tornado intensity changes should be expected if a tornado ascends or descends a hill, or if a taller hill will produce larger intensity changes than a shorter hill. In addition to terrain effects, the varied geometries and layouts of urban structures may impact three-dimensional winds in tornadoes, and as a result, alter tornado damage potential to structures. Finally, combinations of realistic complex terrain with buildings are needed to understand how both factors influence tornado damage potential in areas of complex terrain, such as in the Southeast United States.

The goal of this study is to examine the impacts of terrain and buildings on tornado dynamics using a high-resolution Large-Eddy Simulation (LES) model. The Immersed Boundary Method (IBM) has been implemented in an LES model to examine these effects using a wide range of terrain configurations and buildings. For an isolated buildings, the intensity and frequency of low-level subvortices changes as the tornado passes over or near the building. As the tornado passes directly over the building, strong near-surface radial inflow leads to intense convergence and updrafts along the building’s side walls. Statistical analyses of three-dimensional wind distributions will be conducted for simulations with buildings, terrain, and no terrain to study physical processes responsible for terrain effects. Differences between control, terrain, and building simulations will be quantified to assess their impact on tornado damage potential using the EF-scale standard wind speeds (10-m AGL, 3-s gust).