Dust devil 58161 225663536 2008-07-14T20:10:36Z Rjwilmsi 203434 gen fixes + link/fix date fields in cite templates (explanation [[User:Rjwilmsi#My_correction_of_dates_in_templates|here]]) using [[Project:AutoWikiBrowser|AWB]] [[Image:Mojave DustDevil.jpg|thumb|200px|right|A dust devil in the [[Mojave Desert]]]] {{dablink|For other uses of this phrase, see [[Dust devil (disambiguation)]].}} A '''dust devil''' is a rotating [[vertical draft|updraft]], ranging from small (half a meter wide and a few meters tall) to large (over 10 meters wide and over 1000 meters tall). Dust devils are usually harmless, but rare ones can grow large enough 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 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 "dust whirl".<ref name=death-valley>[http://www.death-valley.us/article559.html http://www.death-valley.us/article559.html]</ref>{{Dead link|date=January 2008 |url=http://www.death-valley.us/article559.html}} The [[Australia]]n "willy-willy" or "whirly-whirly" is thought to derive from [[Yindjibarndi language|Yindjibarndi]] or a neighbouring language.<ref>Dixon et al. (2006): p. 195.</ref> The [[Navajo people|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. [[Egypt]] has its ''fasset el 'afreet'' or "ghost's wind". 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 (Brazilian folklore)|Saci]]. ==Formation== [[Image:Iraqi Dust Devil.jpg|thumb|200px|right|A dust devil in [[Ramadi]], [[Iraq]]]] 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 [[Secondary flow#Tornadoes and dust devils|secondary flow]] in the dust devil 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 upwards and in a circle. As the hot air rises it cools, loses its buoyancy and eventually ceases to rise. As it rises it displaces air which descends outside the core of the vortex. This cool air returning acts as a balance against the spinning hot air outer wall and keeps the system stable.<ref>{{cite book|author = Ludlum, David M. |year = 1997 |title = National Audubon Society Field Guide to North American Weather |publisher = Knopf |id = ISBN 0-679-40851-7}}</ref> 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. 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.<ref name=death-valley/> Certain conditions increase the likelihood of dust devil formation. * '''Flat barren terrain, desert or asphalt:''' Flat conditions increase the likelihood of the hot air "fuel" being a near constant. Dusty or sandy conditions will cause particles to become caught up in the vortex, making the dust devil easily visible. * '''Clear skies or lightly cloudy conditions.''' The surface needs to absorb significant amounts of [[solar power|solar energy]] from the Sun to heat the air near the surface and create ideal dust devil conditions. * '''Light or no wind and cool atmospheric temperature.''' The underlying factor for sustainability of a dust devil is the extreme difference in temperature between the near surface air and atmosphere. Windy conditions will destabilize the spinning effect of a dust devil. ==Intensity and duration== On Earth, most dust devils are very small and weak, often less than 3 feet (0.9 m) in diameter with maximum winds averaging about 45 miles per hour (70 km/h), and they often dissipate less than a minute after forming. On rare occasions, a dust devil can grow very large and intense, sometimes reaching a diameter of up to 300 feet (90 m) with winds in excess of 60 mph (100 km/h), and can last for upwards of 20 minutes before dissipating.<ref>{{cite web | publisher=Arizona Vacation Planner | date=unknown | title=Dust Devils: Ephemeral Whirlwinds Can Stir Up Trouble | url=http://www.arizona-vacation-planner.com/dust-devils.html | accessdate=2007-10-05}}</ref> One such dust devil struck the [[Coconino County, Arizona|Coconino County]] [[Fairgrounds]] in [[Flagstaff, Arizona]] on [[September 14]], [[2000]]. Extensive damage occurred to several temporary tents, stands and booths, as well as some permanent fairgrounds structures. In addition, several injuries were reported, but there were no fatalities. Based on the degree of damage left behind, it is estimated that the dust devil produced winds as high as 75 mph (120 km/h), which is equivalent to a moderate-strength [[Enhanced Fujita Scale|EF0]] tornado.<ref>{{cite web | publisher=National Weather Service-Flagstaff, AZ | date=unknown | title=Damage From a Dust Devil at the Coconino County Fairgrounds - September 14, 2000 | url=http://www.wrh.noaa.gov/fgz/past/cocodust/coco_fair.php?wfo=fgz | accessdate=2007-10-05}}</ref> In 2003, a dust devil lifted the roof off a two-story building in [[Lebanon, Maine]], causing it to collapse and kill a man inside.<ref>[http://www4.ncdc.noaa.gov/cgi-win/wwcgi.dll?wwevent~ShowEvent~499035 NCDC: Event Details] ''[[National Climatic Data Center]]'' Accessed [[2008-06-05]].</ref> ==Electrical activities== Dust devils, even small ones (on Earth) can produce radio noise and electrical fields greater than 10,000 volts per meter.<ref>{{cite press release | publisher=University of California, Berkeley | date=[[29 May]] [[2002]] | title= Stalking Arizona dust devils helps scientists understand electrical, atmospheric effects of dust storms on Mars | url=http://www.berkeley.edu/news/media/releases/2002/05/29_dust.html | accessdate=2006-12-01}}</ref> A dust devil picks up small dirt and dust particles. As the particles 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.<ref>{{cite conference | author=Koch, J., and N.O. Renno | title=Convective-radiative feedback mechanisms by dusty convective plumes and vortices | booktitle=Fall meeting of the American Geophysical Union | year=Dec. 5-9, 2005}}</ref> These electrical fields assist the vortices in lifting materials off the ground and into the atmosphere. Field experiments indicate that a dust devil can lift 1 gram of dust per second from each square meter (10 lb/s from each acre) of ground it passes over. A large dust devil measuring about 100 meters (330&nbsp;ft) across at its base can lift about 15 metric tons (17 short tons) of dust into the air in 30 minutes. Giant dust storms that sweep across the world's deserts contribute eight percent of the mineral dust in the atmosphere each year during the handful of storms that occur. In comparison, the significantly smaller dust devils that twist across the deserts during the summer lift about three times as much dust, thus having a greater combined impact on the dust content of the atmosphere. When this occurs, they are often called '''sand pillars'''.<ref>{{cite journal | first = J.F. | last = Kok | coauthors = Renno, N.O. | year = 2006 | title = Enhancement of the emission of mineral dust aerosols by electric forces | journal = Geophysical Research Letters | volume = 33 | issue = Aug. 28 | pages = L19S10 | doi = 10.1029/2006GL026284 | accessdate = 2006-12-01}}</ref> ==Martian dust devils== [[Image:dust.devil.mars.arp.750pix.jpg|thumb|right|250px|A dust devil on [[Mars (planet)|Mars]], photographed by [[Mars Global Surveyor]]. The long dark streak is formed by a moving swirling column of Martian atmosphere. The dust devil itself (the black spot) is climbing the crater wall. The streaks on the right are sand dunes on the crater floor.]] Dust devils also occur on [[Mars (planet)|Mars]], and were first photographed by the [[Viking program|Viking]] orbiters in the 1970s. In 1997, the [[Mars Pathfinder]] lander detected a dust devil passing over it.<ref>{{cite web | last = Metzger | first = S. M. | url = http://mpfwww.jpl.nasa.gov/science/lpsc98/1915.pdf | title = Dust Devil Vortices at the Ares Vallis MPF Landing Site | format = PDF | work = Mars Exploration Program | publisher = JPL | accessmonthday = December 1 | accessyear = 2006}}</ref><ref>{{cite web | date = [[March 21]] [[2000]] | url = http://www.ruhr-uni-bochum.de/climusa/dust.htm | title = Martian Dust Devils Caught | work = Climate Research USA | publisher = Ruhr-Universität Bochum | accessmonthday = December 1 | accessyear = 2006}}</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>{{cite web | last = Smith | first = Peter | coauthors = Renno, Nilton | date = [[6 June]] [[2001]] | url = http://unisci.com/stories/20012/0606012.htm | title = Studying Earth Dust Devils For Possible Mars Mission | publisher = UniSci News | accessmonthday = December 1 | accessyear = 2006}}</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 dramatically increased and daily science work was anticipated to be expanded.<ref>{{cite web | last = David | first = Leonard | date = [[12 March]] [[2005]] | url = http://www.space.com/missionlaunches/spirit_dust_050312.html | title = Spirit Gets A Dust Devil Once-Over | publisher = Space.com | accessmonthday = December 1 | accessyear = 2006}}</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.<ref>{{cite web | url = http://athena.cornell.edu/kids/did_you_know.html | title = Did You Know? | work = Mars Exploration Rovers | publisher = Cornell University | accessmonthday = December 1 | accessyear = 2006}}</ref> <br clear="all"/> [[Image:Marsdustdevil2.gif|thumb|center|580px|Dust devil on Mars, photographed by the Mars rover ''Spirit''. The counter in the bottom-left corner indicates time in seconds after the 1st photo was taken in the sequence. Three other dust devils appear in the background.]] ==Related phenomena== A [[Fire whirl]] or swirl, sometimes called fire devils or fire tornadoes, can be seen during intense fires in combustible building structures or more commonly in forest or bush fires. A fire whirl is a vortex-shaped formation of burning gases being released from the combustible material. The genesis of the vortex is probably similar to that of a dust devil. But, as distinct from the dust devil, it is improbable that the height reached by the fire gas vortex is greater than the visible height of the vortical flames because of turbulence in the surrounding gases which inhibit creation of a stable boundary layer between the rotating/rising gases relative to the surrounding gases.<ref>[http://jfsp.nifc.gov/conferenceproc/GISRS-12-AORadkeetal.pdf WILDFIRE MODELING, IR OBSERVATIONS AND ANALYSIS]</ref> Hot cinders underneath freshly-deposited ash in recently burned areas may sometimes generate numerous dust devils. The lighter weight and the darker color of the ash may create dust devils that are visible hundreds of feet into the air. [[Steam devils]] are phenomena often observed in the steam rising from [[power plant]]s.<ref name="Handy Weather Answer Book"> Lyons, Walter A. <u>The Handy Weather Answer Book</u>. Detroit, MI: Visible Ink Press, 1997.</ref> ==See also== *[[Gustnado]] *[[Tornado]] *[[Fire whirl]] *[[Steam devil]] *[[Waterspout]] *[[Landspout]] *[[Secondary flow]] ==Notes== {{reflist}} ==References== *{{cite book |author=Dixon, R.M.W.; Moore, Bruce; Ramson, W. S.; Thomas, Mandy |year=2006 |title=Australian Aboriginal Words in English: Their Origin and Meaning |edition=2nd ed. |location=South Melbourne |publisher=Oxford University Press |isbn=0-19-554073-5}} ==External links== {{commons|Dust devil}} *[http://www.inflowimages.com/ChaseReports/DustDevils/dustdevils.asp Australian Dust Devil Photos] *[http://www.animalu.com/pics/dd1.htm ''Dancing with the Devils'' Video] *[http://www.nasa.gov/vision/universe/solarsystem/mer-042105.html Dust Devil Imaged by ''Spirit'' Rover on Mars] *[http://video.google.com/videoplay?docid=-5412742731312666511&q=Dust+Devil&total=476&start=0&num=10&so=0&type=search&plindex=1 Japanese Dust Devil Video] *[http://www.lpl.arizona.edu/IMP/Matador/ Matador Dust Devil Project] *[http://www.lpl.arizona.edu/~lemmon/mer_dd.html Page with many movies] of Martian dust devils as seen by Spirit, with enhanced images as well as ratings. *[http://www.lbk.ars.usda.gov/wewc/biblio/bar.htm The Bibliography of Aeolian Research] [[Category:Winds]] [[Category:Mars]] [[Category:Vortices]] [[de:Kleintrombe]] [[el:Ανεμοστρόβιλος]] [[fa:تنوره دیو]] [[fr:Tourbillon de poussière]] [[ko:회오리바람]] [[it:Diavolo di sabbia]] [[he:עלעול חול]] [[nl:Stofhoos]] [[ja:塵旋風]] [[no:Støvvirvel]] [[nn:Støvkvervel]] [[pt:Redemoinho]] [[fi:Pölypyörre]] [[zh:旋风]]