Dynamics of the Tornado Vortex

David Nolan, University of Miami
October 30th, 2013 at 3:30PM–4:30PM in 939 Evans Hall [Map]

In the first part of this talk, I will review the basic mechanisms for all tornado-like vortices (tornadoes, waterspouts, and dust devils). Our current understanding of what controls their intensity, structure, and dynamics comes from both laboratory experiments and numerical simulations. In particular, the "thermodynamic speed limit" sets an upper limit on the maximum mean wind speeds that is fairly low compared to the levels of damage that are found in the most extreme events.

The most extreme wind speeds are associated with asymmetric, coherent structures such as "multiple vortices" that are often visible in photographs and videos. A new analysis of the multiple vortex phenomenon will be presented using much more realistic representations of the tornado-vortex flow than had been used in some earlier studies. The linearized stability analysis successfully predicts the dominant structures in unsteady, three-dimensional simulations. In addition, symmetric modes are identified that may explain symmetric oscillations that have been directly observed in real tornadoes.