Dust devil
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- For the minor-league baseball team, please see Tri-City Dust Devils.
- For the 1993 film, please see Dust Devil (1993 film).
Image:Whirlwind9832.jpg A dust devil or whirlwind is either a large rotating updraft, anywhere from 1000 meters high or more and tens of meters in diameter, or a small vortex a few meters high. In Australia, they are commonly known as willy willies, from an Aboriginal word.
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Causes of dust devils
Dust devils form in areas of strong surface heating, typically under clear skies and light winds, when the sun can warm the air near the ground to temperatures well above those just above the surface layer. Once the ground heats up enough, a localized pocket of air will quickly rise through the cooler air above it. The sudden upward rush of hot air causes air to speed horizontally inward to the bottom of the newly forming vortex. As more hot air rushes in toward the developing vortex to replace the air that is rising, the spinning effect is intensified. The dust devil, once formed, is a funnel-like chimney through which hot air moves both upwardly and circularly. If a steady supply of warm unstable air is available for the dust devil, it will continue to move across the ground. However, once the warm unstable air is used up, the dust devil ends.<ref>Template:Cite bookLudlum, David M. |year = 1997 |title = National Audubon Society Field Guide to North American Weather |publisher = Knopf |id = ISBN 0679408517}}</ref>
Smaller dust devils
The smaller dust devils reach only a few meters or tens of meters in height, forming commonly in hot dry weather, most observably in fields or dusty flats, where the soil makes them visible, and which may be shorter-lived.
Electrical activities
It was recently found that even small dust devils (on Earth) can produce radio noise and electrical fields greater than 10,000 volts per meter.<ref>[1]</ref>
Martian dust devils
Image:Dust.devil.mars.arp.750pix.jpg
Dust devils also occur on Mars, and were first photographed by the Viking orbiters in the 1970s. In 1997, the Mars Pathfinder lander detected a dust devil passing over it. <ref name=dustdevil>Metzger S. M., Dust Devil Vortices at the Ares Vallis MPF Landing Site (PDF)</ref><ref>[2]</ref> Martian dust devils can be up to fifty times as wide and ten times as high as terrestrial dust devils, and large ones may pose a threat to terrestrial technology sent to Mars.<ref>[3]</ref>
Mission members monitoring the Spirit rover on Mars reported March 12, 2005 that a lucky encounter with a dust devil has cleaned the solar panels of that robot. Power levels have dramatically increased and daily science work is anticipated to be expanded. <ref>(space.com)</ref> A similar phenomenon (solar panels mysteriously cleaned of accumulated dust) had previously been observed with the Opportunity rover, and dust devils had also been suspected as the cause.
A large-scale cyclone has also been observed on Mars.
Image:Marsdustdevil2.gif
References
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