A
dust devil is a strong, well-formed, and relatively long-lived
whirlwindA whirlwind is a weather phenomenon in which a vortex of wind forms due to instabilities and turbulence created by heating and flow gradients. Whirlwinds occur all over the world and in any season....
, 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 rare ones can grow large enough to threaten both people and property.
They are comparable to
tornadoA tornado is a violent, dangerous, rotating column of air which is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud...
es in that both are a weather phenomenon of a vertically oriented rotating column of air. Most tornadoes are associated with a larger parent circulation, the
mesocycloneA mesocyclone is a vortex of air, approximately 2 to 10 km in diameter , within a convective storm....
on the back of a
supercellA supercell is a thunderstorm that is characterized by the presence of a mesocyclone; a deep, continuously-rotating updraft. Of the four classifications of thunderstorms , supercells are the overall least common and have the potential to be the most severe...
thunderstormA thunderstorm, also known as an electrical storm, a lightning storm, a hailstorm, or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically-assigned cloud type associated with the...
. 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" or a "sun devil". In Death Valley, California, it may be called a "sand auger" or a "dust whirl".
The
NavajoThe Navajo or Diné of the Southwestern United States are the second largest Native American tribe of Northern America. In the 2000 U.S. census, 298,197 people claimed to be fully or partly of Navajo ancestry. The Navajo Nation constitutes an independent governmental body which manages 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
AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the continental mainland , the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans...
n "willy-willy" or "whirly-whirly" is thought to derive from Yindjibarndi or a neighboring 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
BrolgaThe Brolga , formerly known as the "Native Companion", is a bird in the crane family. The bird has also been given the name "Australian Crane", a term coined in 1865 by well-known ornithological artist John Gould in his Birds of Australia.The Brolga is a common gregarious wetland bird species in...
where 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 ArabiaSaudi Arabia , is an Arab country and the largest country of the Arabian Peninsula. It is bordered by Jordan on the northwest, Iraq on the north and northeast, Kuwait, Qatar, Bahrain, and the United Arab Emirates on the east, Oman on the southeast, and Yemen on the south...
,
KuwaitThe State of Kuwait is a sovereign Arab emirate bordered by Saudi Arabia to the south and Iraq to the north and west. The greatest distance from north to south is 200 km and from east to west 170 km . The name is a diminutive of an Arabic word meaning "fortress built near water." It has a...
,
IranIran , officially the Islamic Republic of Iran is a country in Western Asia. The name Iran has been in use natively since the Sassanid period and came into international use from 1935, before which the country was known internationally as Persia...
,
KazakhstanKazakhstan , officially the Republic of Kazakhstan, is a country situated in Eurasia that is ranked as the ninth largest country in the world. It is also the world's largest landlocked country. Its territory of 2,727,300 km² is greater than Western Europe...
, and
JordanJordan , officially the Hashemite Kingdom of Jordan, is a country in Western Asia spanning the southern part of the Syrian Desert down to the Gulf of Aqaba. Jordan shares borders with Syria to the north, Iraq to the northeast, Saudi Arabia to the east and south, the Gulf of Aqaba to the southwest,...
, they often reach hundreds of meters in height and are referred to as
djin ("genies" or "devils").
EgyptEgypt , officially the Arab Republic of Egypt, is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Western Asia...
has its
fasset el 'afreet, or "ghost's wind".
Among the
KikuyuThe Kikuyu are Kenya's most populous ethnic group. 'Kikuyu' is the Swahilized form of the proper name and pronunciation of Gĩkũyũ although they refer to themselves as the Agĩkũyũ people....
of
KenyaThe Republic of Kenya is a country in East Africa. Lying along the Indian Ocean, at the equator, Kenya is bordered by Ethiopia , Somalia , Tanzania , Uganda plus Lake Victoria , and Sudan . The capital city is Nairobi. Kenya spans an area about 85% the size of France or Texas...
, the dust devil is known as
ngoma cia aka, meaning "women's devil/demon".
In
BrazilBrazil , officially the Federative Republic of Brazil , is a country in South America. It is the fifth largest country by geographical area, occupying nearly half of South America, the fifth most populous country, and the fourth most populous democracy in the world. Bounded by the Atlantic Ocean...
, a dust devil is called
redemoinho after
moinho de vento ("
windmillA windmill is a machine which translates linear motion of wind to rotational motion by means of adjustable vanes called sails. The main use is for a grinding mill powered by the wind, reducing a solid or coarse substance into pulp or minute grains by crushing, grinding, or pressing...
"). In some traditions, it contains a dancing
SaciThe Saci is arguably the most popular character in Brazilian folklore. He is a one-legged black or mulatto youngster with holes in the palms of his hands, who smokes a pipe and wears a magical red cap that enables him to disappear and reappear wherever he wishes...
. Also in
PortugalPortugal , officially the Portuguese Republic , is a country located in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of mainland Europe and is bordered by the Atlantic Ocean to the west and south and by Spain to the north and east...
know locally as
remoinho (translated to
continuous rotation).
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 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.
The spinning effect, along with surface
frictionFriction is the force resisting the relative lateral motion of solid surfaces, fluid layers, or material elements in contact. It is usually subdivided into several varieties:...
, 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 the dust devil is not 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.
- 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 energy
Solar energy, radiant light and heat from the Sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...
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 the 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. One such dust devil struck the
Coconino CountyCoconino County is a county located in the north central part of the U.S. state of Arizona. It is part of the Flagstaff, Arizona Metropolitan Statistical Area. The population was 116,320 at the 2000 census; the 2007 estimated population is 127,450. The county seat is Flagstaff...
Fairgrounds in
Flagstaff, ArizonaFlagstaff is a city located in northern Arizona, in the southwestern United States. In July 2006, the city's estimated population was 58,213. The population of the Metropolitan Statistical Area was estimated at 127,450 in 2007. It is the county seat of Coconino County...
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
EF0The Enhanced Fujita Scale, or EF Scale, is the scale for rating the strength of tornadoes in the United States estimated via the damage they cause....
tornado.
On May 19, 2003, a dust devil lifted the roof off a two-story building in
Lebanon, MaineLebanon is a town in York County, Maine, United States. The population was 5,083 at the 2000 census. Lebanon includes the villages of Center Lebanon, West Lebanon, North Lebanon, South Lebanon and East Lebanon. It is part of the Portland–South Portland–Biddeford, Maine Metropolitan...
, causing it to collapse and kill a man inside.. On June 18, 2008, a dust devil collapsed a shed near
Casper, WyomingCasper is the only city in and the county seat of Natrona County, Wyoming, United States. With a population of 49,644, Casper is the second largest city in Wyoming, according to the 2000 census...
, killing a woman.
Electrical activities
Dust devils, even small ones (on Earth), can produce radio noise and electrical fields greater than 10,000 volts per meter. 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.
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 ft) across at its base can lift about 15 metric tonnes (17 short tons) of dust into the air in 30 minutes. Giant dust storms that sweep across the world's deserts contribute 8% 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.
Martian dust devils
Dust devils also occur on
MarsMars is the fourth planet from the Sun in the Solar System. The planet is named after Mars, the Roman god of war. It is also referred to as the "Red Planet" because of its reddish appearance, due to iron oxide prevalent on its surface....
and were first photographed by the
VikingNASA's Viking program consisted of a pair of space probes sent to Mars, Viking 1 and Viking 2. Each vehicle was composed of two main parts, an orbiter designed to photograph the surface of Mars from orbit, and a lander designed to study the planet from the surface...
orbiters in the 1970s. In 1997, the
Mars PathfinderThe Mars Pathfinder later called The Carl Sagan Memorial Station was launched on December 4, 1996 by NASA aboard a Delta II just a month after the Mars Global Surveyor was launched. After a 7-month voyage it landed on Ares Vallis, in a region called Chryse Planitia on Mars, in the Oxia Palus...
lander detected a dust devil passing over it. 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.
Mission members monitoring the
Spirit roverSpirit, mission designation MER-A , is the first of the two rovers of NASA's Mars Exploration Rover Mission. It landed successfully on Mars on 04:35 Ground UTC on January 4, 2004, three weeks before its twin Opportunity landed on the other side of the planet...
on Mars reported on March 12, 2005, that a lucky encounter with a dust devil had cleaned the solar panels of that robot. Power levels dramatically increased and daily science work was anticipated to be expanded. A similar phenomenon (solar panels mysteriously cleaned of accumulated dust) had previously been observed with the
Opportunity roverOpportunity, mission designation MER-B , is the second of the two rovers of NASA's Mars Exploration Rover Mission. It landed successfully at Meridiani Planum on Mars on January 25, 2004 05:05 Ground UTC , three weeks after its twin Spirit had landed on the other side of the planet...
, and dust devils had also been suspected as the cause.
Related phenomena
A
fire whirlA fire whirl, colloquially fire devil or fire tornado, is a rare phenomenon in which a fire, under certain conditions , acquires a vertical vorticity and forms a whirl, or a tornado-like effect of a vertically oriented rotating column of air...
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. 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 vertical flames because of turbulence in the surrounding gases that inhibit creation of a stable boundary layer between the rotating/rising gases relative to the surrounding gases.
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 devilA steam devil is the term used to describe a rotating updraft that involves steam or smoke. Steam devils usually occur above power plants, and rarely occur elsewhere, though they may occur in deserts or other dry and arid locations...
s are phenomena often observed in the steam rising from power plants.
See also
- Gustnado
A gustnado is a specific type of short-lived, low-level cyclonic cloud that can form in a severe thunderstorm. The name is a portmanteau of "gust front tornado", as gustnadoes form due to non-tornadic cyclonic features in the downdraft from the gust front of a strong thunderstorm, especially one...
- Tornado
A tornado is a violent, dangerous, rotating column of air which is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud...
- Waterspout
A waterspout is an intense columnar vortex that occurs over a body of water and is connected to a cumuliform cloud. In the common form, it is a non-supercell tornado over water. While it is often weaker than most of its land counterparts, stronger versions spawned by mesocyclones do occur...
- Landspout
A landspout is a slang-term coined by meteorologist Howard B. Bluestein in 1985 for a kind of tornado not associated with the mesocyclone of a thunderstorm...
- Secondary flow
In fluid dynamics, a secondary flow is a relatively minor flow superimposed on the primary flow, where the primary flow usually matches very closely the flow pattern predicted using simple analytical techniques and assuming the fluid is inviscid...
- Steam devil
A steam devil is the term used to describe a rotating updraft that involves steam or smoke. Steam devils usually occur above power plants, and rarely occur elsewhere, though they may occur in deserts or other dry and arid locations...
- Storm
A storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather...
- Fire Whirl
A fire whirl, colloquially fire devil or fire tornado, is a rare phenomenon in which a fire, under certain conditions , acquires a vertical vorticity and forms a whirl, or a tornado-like effect of a vertically oriented rotating column of air...
External links