This is an interesting data set from NCSA.  I don't know much more 
about it except that it came from Brain Kowalski and included this
description:

This model is a simple model of a tornado-like flow assuming symmetry
in the azmuthial direction.  It is not a a tornado flow, since
there is no three dimensionality in it.  The initial conditions
are specified from an idealized model.


Good luck
Rich Johnson
richj@stardent.com
(617)964-1000