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).
A dust devil or whirlwind is a rotating updraft, ranging from small (half a meter wide and a few meters tall) to large (over 10 meters wide and over 1000 meters tall). In Australia, they are commonly known as willy willies, from an Aboriginal word. Dust devils can be dangerous or harmless depending on their size. They are comparable to tornadoes, but form during fair weather and are very rarely as strong.
A dangerous dust devil was created in Trenton, North Dakota on May 7, 2006 that lifted a 4-year old girl and the trampoline she was jumping on 25 feet (approximately 8 metres) into the air. The girl survived with only moderate injuries.http://edition.cnn.com/2006/WEATHER/05/08/whirlwind.ap/index.html
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.Smaller dust devils
Smaller dust devils, forming in hot dry weather, rarely reach more then a few meters in height. Commonly, dust devils form in fields or dusty flats, where the soil makes them more visible.The phenomenon that forms dust devils can even develop over dry pavement. It is observable when it passes by a person, or there is litter such as leaves or paper on the pavement.
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.http://www.berkeley.edu/news/media/releases/2002/05/29_dust.htmlMartian dust devils
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. Metzger S. M., [Dust Devil Vortices at the Ares Vallis MPF Landing Site] (PDF)http://www.ruhr-uni-bochum.de/climusa/dust.htm 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.http://unisci.com/stories/20012/0606012.htm
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 dramatically increased and daily science work was anticipated to be expanded. [(space.com)] 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. http://athena.cornell.edu/kids/did_you_know.html
A large-scale cyclone has also been observed on Mars.
References
External links
- [Australian Dust Devil Photos]
- [Dancing with the Devils Video]
- [Dust Devil Imaged by Spirit Rover on Mars]
- [Japanese Dust Devil Video]
- [Matador Dust Devil Project]
- [Page with many movies] of martian dust devils as seen by Spirit, with enhanced images as well as ratings.
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