Dust Devils
http://en.wikipedia.org/wiki/Dust_devil
Dust devils form when extremely hot air near the surface rises
quickly through a small pocket of cooler low pressure air above it. If
conditions are just right, the air may begin to rotate. As the air rises
suddenly, the column of hot air is stretched vertically causing intensification
of the spinning effect by the scientific principle conservation of angular
momentum.
Thanks to Ole.
http://OzReport.com/10.182.2
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