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A numerically-simulated tornado moving from left to right at
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A numerically-simulated tornado moving from left to right at 15 miles per second as it ingests

June 9, 2010
A numerically-simulated tornado moving from left to right at 15 miles per second as it ingests 1mm-diameter sand from the surface. Note the thin surface layer that is feeding into the turbulent debris cloud and centrifuging out around the lower part of the funnel, formed from condensing water droplets. This research was supported by National Science Foundation (NSF) grant ATM 0236667. (Date of Image: August 2004)

More about this Image This image was created from numerical simulation data was custom-made ray-casting and lighting software. For the funnel cloud, the condensed water vapor at each point was calculated from simulated pressure values, assuming a reasonable temperature and water vapor mixing ratio. Both condensed water droplets (white) and debris particles (brown) were then treated as solid-color fields of varying opacities, illuminated by a spotlight to the right and a constant ambient lighting.

The numerical simulation involves an unsteady, fully 3-Dimensional high-resolution computation of the basic fluid dynamic equations including fine debris as a second fluid. This research is part of a continuing effort (sponsored by NSF on the near-surface intensification of tornado winds. It has shown that the presence of debris can significantly change the structure of low-level winds in a tornado (see paper #15.5, American Meteorological Society's 22nd Conference on Severe Local Storms, October 2004, [http://ams.confex.com/ams/pdfpapers/81449.pdf]). The local debris mass near the surface can significantly exceed that of the air and remain important to altitudes of several 100 meters, particularly when fine particles are available to be picked up from the surface. For different conditions, the addition of debris can either increase or decrease the damage potential of the tornado.


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