Abstract:

In a tornadic supercell velocities are intensified within a small region of the storm, within a few tens of meters of the surface where they can do the most damage.  This talk focuses on two closely related ingredients in this process: the near-surface intensification of a tornado due to fluid-dynamic effects, and the great sensitivity of tornado behavior to near-surface conditions. Results from numerical large-eddy simulations together with theoretical analysis will be used to explore these phenomena, demonstrating that even modest changes in near-surface conditions can sometimes dramatically change tornado behavior and showing how near-surface intensification of an order of magnitude or greater relative to conditions aloft can be produced. Included will be examples of the effects of idealized topography, buildings and debris on tornado dynamics.

Bio:

David Lewellen received a BSE in Mechanical and Aerospace Engineering from Princeton University in 1982. This was followed by an extended sojourn into elementary particle physics and superstring theory with a PhD in Physics from Cornell in 1987 and research positions at the Stanford Linear Accelerator Center (SLAC) and the Institute for Theoretical Physics at UCSB. In 1993 he returned to his fluid dynamics roots, joining the research faculty at West Virginia University in order to work with his father on problems in the atmospheric sciences. He has been there ever since, using numerical simulations and theoretical analysis to study a variety of problems, most extensively dealing with the atmospheric boundary layer, tornadoes, and aircraft wakes and contrails.