AbstractAbstractThis study investigates the effects of idealized and realistic terrain on tornado characteristics and behavior. It uses a novel simulation approach, nesting a high-fidelity, ultrafine-resolution, tornado-scale, engineering large-eddy simulation (LES) within a Cloud Model 1 (CM1) simulation of a tornadic supercell. We analyze the effects of terrain on the tornado’s central pressure, horizontal and vertical velocities, vortex shape, and path. Seven idealized terrain configurations are used including 1) a control run with flat ground, 2) and 3) an idealized hill with steep and gradual slopes having the height of 25.4 m, 4) and 5) an idealized escarpment with steep and gradual slopes having the height of 25.4 m, and 6) and 7) an idealized hill having heights of either 50 or 65 m. Furthermore, a real-world, complex terrain configuration of the same height is analyzed as the eighth case. Results suggest that the presence of terrain relief increases the central pressure deficit, the peak wind speed, and the width of the high wind speed region in the tornado swath, enhancing tornado intensity and causing path deviation. Specifically, the horizontal and vertical velocities at 10 m above ground level (AGL) are stronger with terrain and the location of the maximum pressure deficit occurs along the uphill segment for all idealized cases except the steep hill. The precise location of the maximum wind velocities and pressure deficits varies with the terrain shape and slope. The real terrain simulation is similar to the idealized terrain simulations to a certain extent; however, the vertical velocities are lower and the strongest winds occur over a smaller region, demonstrating the complexity of the tornado–terrain relationship.Significance StatementThis high-resolution numerical study investigates the effects that idealized hills and escarpments have on tornadoes and offers a comparison with a real-world, complex terrain configuration. This study is particularly novel for three reasons: 1) The nested simulation approach with an ultrafine inner grid (spacing of 0.01 m) facilitates a high-fidelity vortex simulation which reflects the variability of a real-world tornado in time and space, at a reasonable computation cost; 2) the ultrafine-scale LESs resolve turbulent features to this spatial scale and facilitate better characterization of tornadic winds; and 3) an experiment having real-world, complex terrain is successfully executed for the first time in tornado research (to the authors’ knowledge). Results suggest that terrain generally causes tornadoes to become stronger and wider than they otherwise would have been if the ground were flat. However, another important result is that the effects of the real-world, complex terrain on the tornado are not the same as those from simplified terrains.
