Indiana Section of the Mathematical Association of America

Spring 2004 Meeting

 

April 2-3, 2004

 

Indiana State University

Terre Haute, Indiana

 

 

What Do Tornados Look Like?

(Friday after Dinner Talk)

 

The Swirling Vortex: A Mathematical Model for Tornadoes

(Saturday Plenary Talk)

 

Professor James Serrin

University of Minnesota

 

 

We discuss the dynamical interaction of a central vortex flow with a plane surface, a situation which occurs when a tornado makes contact with the ground. This interaction leads to a secondary swirling flow within the vortex, which can be of several different types depending on the coherence of the vortex.

 

Among the possible kinds of induced secondary flows superimposed on the main vortex, there are those with central updrafts (this type presumably carried Dorothy to the Land of Oz). More surprisingly, however, there are others which have a central downdraft, these being associated with a cascade or fountain effect at the point of contact.

 

The latter motions are of particular interest in explaining the cascade behavior observed in actual tornadoes, as seen in photographs and video recordings taken by eyewitnesses. Some of these remarkable videos will be presented during the after dinner lecture.