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A dust devil is a strong, well-formed, and relatively long-lived whirlwind, ranging from small (half a meter wide and a few meters tall) to large (more than 10 meters wide and more than 1000 meters tall). The primary vertical motion is upward. Dust devils are usually harmless, but can on rare occasions grow large enough to pose a threat to both people and property. They are comparable to tornadoes in that both are a weather phenomenon of a vertically oriented rotating column of wind. Most tornadoes are associated with a larger parent circulation, the mesocyclone on the back of a supercell thunderstorm. Dust devils form as a swirling updraft under sunny conditions during fair weather, rarely coming close to the intensity of a tornado. == Names == In the southwestern United States, a dust devil is sometimes called a "dancing devil". In Death Valley, California, it may be called a "sand auger" or a "dust whirl". The Navajo refer to them as ''chiindii'', ghosts or spirits of dead Navajos. If a chindi spins clockwise, it is said to be a good spirit; if it spins counterclockwise, it is said to be a bad spirit. The Australian English term "willy-willy" or "whirly-whirly" is thought to derive from Yindjibarndi or a neighbouring language. In Aboriginal myths, willy-willies represent spirit forms. They are often quite scary spirits, and parents may warn their children that if they misbehave, a spirit will emerge from the spinning vortex of dirt and chastise them. There is a story of the origin of the brolga in which a bad spirit descends from the sky and captures the young being and abducts her by taking the form of a willy-willy. In Saudi Arabia, Kuwait, Kazakhstan, and Jordan, they often reach hundreds of meters in height and are referred to as ''djin'' ("genies" or "devils"). Egypt has its ''fasset el 'afreet'', or "ghost's wind". In Iran, this kind of wind is usually called "Gerd Baad", or "round wind".〔http://pakistanweatherportal.com/2012/04/21/seraki-myth-dust-storms-are-possessed-by-demons/〕 Among the Kikuyu of Kenya, the dust devil is known as ''ngoma cia aka'', meaning "women's devil/demon". In Brazil, a dust devil is called ''redemoinho'' after ''moinho de vento'' ("windmill"). In some traditions, it contains a dancing Saci. Also, sometimes it is associated to local religion and beliefs.〔http://extestemunhasdejeova.net/forum/viewtopic.php?f=20&t=10899〕 In Portugal it is known locally as ''remoinho'' (translated to ''continuous rotation''). In the US, when they occur in cities or urban scenes, they are sometimes called "Nevada tornadoes" or "Chicago tornadoes" because of Chicago's reputation for wind, despite dust devils being rare in Chicago. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dust devil」の詳細全文を読む スポンサード リンク
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