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Dust Devils
Tue May 31, 2005
Listen in RealAudio 
In their most impressive state, dust devils are often confused with tornadoes. While
similar in many aspects, they are also very different from their destructive cousins. Hi,
I'm Bryan Yeaton for The Weather Notebook.
Dust devils emerge from large rotating columns of rising air. The second most
common natural atmospheric vortex, they can be found almost anywhere, even Mars.
An estimated ten dust devils are churning the Earth at this moment.
When under intense solar heating, surface temperatures soar, often as high as 130
degrees, and this generates hot air columns, rising as invisible chimneys. As this air
rises, something gives it a little spin perhaps the breeze aloft, perhaps a passing car
at ground level.
If the whirling updraft column continues to intensify, the vortex tightens and thus rotates
faster, like a spinning figure skater. When the invisible winds pick up loose surface
dust, a dust devil is born.
The largest dust devils can spread to 300 yards wide and hundreds of feet tall, but
most often they are only a few feet in diameter and less than 100 in height. Their
lifespan is typically 15 minutes, though a well-established devil can persist for an
hour.
Because of their small size and brief life, dust devils are not influenced by the Coriolis
parameter and thus may rotate either clockwise or counterclockwise.
Average dust devil winds swirl at 20 mph, but strong ones have been clocked at 90
mph. And once established, they tear forward across the terrain at 15 to 60
mph.
Thanks to our contributing writer, meteorologist Keith Heidorn. The Weather Notebook
receives funding from Subaru of America and The National Science Foundation.
Today's Links
Observing Dust Devils
http://www.australiasevereweather.com/techniques/moreadv/funnels.htm#3
Dust Devils
http://members.attcanada.ca/~stefanac/weather/dustdevils.html
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