Information AboutDust Devil |
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| dust devil | |
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, Iraq .]] .]] A dust devil 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 the southwestern United States, dust devils can be known as '''dancing devils'''. Navajo refer to them as Chiindii , a ghost or spirit of a Navajo. If a chiindii spins clockwise it is said to be a good spirit; if it spins counterclockwise it is said to be a bad spirit. In Death Valley, California, they may be called a '''sand auger''' or '''dust whirl'''. In Australia , they are commonly known as a willy willy, from an Aboriginal word. 1 In Egypt, they are usually called "Fasset El 'Afreet" or the ghost's wind. Dust devils are usually harmless, but rare ones can grow in size to threaten both people and property. They are comparable to Tornadoes in that both are an unusual weather phenomenon of swirling air vortices. Tornadoes form as an updraft attached to a wall cloud at the back of a thunderstorm. Dust devils form as an updraft under sunny conditions during clear to fair weather, rarely coming close to the intensity of a tornado. FORMATION Dust devils form when 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 . The spinning effect causes other hot 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 becomes further intensified and self-sustaining. A dust devil, fully formed, is a funnel-like chimney through which hot air moves both upwardly and circularly. Eventually the hot air will cool and descend back through the center of the vortex. This cool air returning acts as a balance against the spinning hot air outer wall and keeps the system stable.2 The spinning effect, along with surface Friction , usually will produce a forward momentum. The dust devil is able to sustain itself longer by moving over nearby sources of hot surface air. Dust particles sucked into the air will create Drag and act to slow the system down. As available extreme hot air near the surface is channeled up the dust devil, eventually surrounding cooler air will be sucked in. Once this occurs, the effect is dramatic and the dust devil dissipates in seconds. Usually this occurs when a dust devil isn't moving fast enough (depletion) or begins to enter a terrain where the surface temperatures are cooler, causing unbalance. Certain conditions increase the likelihood of dust devil formation.
ELECTRICAL ACTIVITIES Dust devils, even small ones (on Earth) can produce radio noise and electrical fields greater than 10,000 volts per meter.3 A dust devil picks up small dirt and dust particles. As the particle whirl around they bump and scrape into each other and become electrically charged. The whirling charged particles also create a magnetic field that fluctuates between 3 and 30 times each second.4 |
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