A dust devil in Arizona.
|Area of occurrence||Primarily temperate and tropical regions.|
|Season||Most common in summer.|
|Effect||Dust and debris lofted into air, possibly wind damage.|
|Part of the nature series|
A dust devil is a strong, well-formed, and relatively long-lived whirlwind, ranging from small (half a metre wide and a few metres tall) to large (more than 10 metres wide and more than 1000 metres 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.
A whirlwind is a weather phenomenon in which a vortex of wind forms due to instabilities and turbulence created by heating and flow (current) gradients. Whirlwinds occur all over the world and in any season.
They are comparable to tornadoes in that both are a weather phenomenon involving 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.
A tornado is a rapidly rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. The windstorm is often referred to as a twister, whirlwind or cyclone, although the word cyclone is used in meteorology to name a weather system with a low-pressure area in the center around which, from an observer looking down toward the surface of the earth, winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern. Tornadoes come in many shapes and sizes, and they are often visible in the form of a condensation funnel originating from the base of a cumulonimbus cloud, with a cloud of rotating debris and dust beneath it. Most tornadoes have wind speeds less than 110 miles per hour (180 km/h), are about 250 feet (80 m) across, and travel a few miles before dissipating. The most extreme tornadoes can attain wind speeds of more than 300 miles per hour (480 km/h), are more than two miles (3 km) in diameter, and stay on the ground for dozens of miles.
A mesocyclone is a vortex of air within a convective storm. It is air that rises and rotates around a vertical axis, usually in the same direction as low pressure systems in a given hemisphere. They are most often cyclonic, that is, associated with a localized low-pressure region within a severe thunderstorm. Such thunderstorms can feature strong surface winds and severe hail. Mesocyclones often occur together with updrafts in supercells, within which tornadoes may form at the interchange with certain downdrafts.
A supercell is a thunderstorm characterized by the presence of a mesocyclone: a deep, persistently rotating updraft. For this reason, these storms are sometimes referred to as rotating thunderstorms. Of the four classifications of thunderstorms, supercells are the overall least common and have the potential to be the most severe. Supercells are often isolated from other thunderstorms, and can dominate the local weather up to 32 kilometres (20 mi) away. They tend to last 2-4 hours.
Dust devils form when a pocket of hot air near the surface rises quickly through cooler air above it, forming an updraft. If conditions are just right, the updraft may begin to rotate. As the air rapidly rises, the column of hot air is stretched vertically, thereby moving mass closer to the axis of rotation, which causes intensification of the spinning effect by 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 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.[ citation needed ]
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction:
As available 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.
Certain conditions increase the likelihood of dust devil formation.
On Earth, many dust devils are usually 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.
Dust devils typically do not cause injuries, but rare, severe dust devils have caused damage and even deaths in the past. One such dust devil struck the Coconino County Fairgrounds in Flagstaff, Arizona, on September 14, 2000, causing extensive damage to several temporary tents, stands and booths, as well as some permanent fairgrounds structures. 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 an EF-0 tornado. On May 19, 2003, a dust devil lifted the roof off a two-story building in Lebanon, Maine, causing it to collapse and kill a man inside. In East El Paso, Texas in 2010, three children in an inflatable jump house were picked up by a dust devil and lifted over 10 feet (3 m), traveling over a fence and landing in a backyard three houses away. In Commerce City, Colorado in 2018, a powerful dust devil hurtled two porta-potties into the air. No one was injured in the incident. In 2019 a large dust devil in Yucheng county, Henan province, China killed 2 children and injured 18 children and 2 adults when a bouncy castle was lifted into the air.
Dust devils have been implicated in around 100 aircraft accidents.While many incidents have been simple taxiing problems, a few have had fatal consequences. Dust devils are also considered major hazards among skydivers and paragliding pilots as they can cause a parachute or a glider to collapse with little to no warning, at altitudes considered too low to cut away, and contribute to the serious injury or death of parachutists.
There is an endemic disease in some arid areas, such as the southwestern United States, California, northwestern Mexico, Central America, and South America, called Valley fever. “Cocci” fungus grows naturally in alkaline soil and the fungus spores that lie dormant and can be picked up by dust devils, are blown around. When a person or animal breathes these spores in, they cause fungal pneumonia. While usually not a serious threat, this disease is still dangerous to some people and animals, especially if they are old or young.
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 electric fields may assist the vortices in lifting material 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 metre (10 lb/s from each acre) of ground over which it passes. A large dust devil measuring about 100 metres (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.
Dust devils also occur on Mars (see dust devil tracks) and were first photographed by the Viking orbiters in the 1970s. In 1997, the Mars Pathfinder lander detected a dust devil passing over it.In the image shown here, photographed by the 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.
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.On 7 November 2016, five such dust devils ranging in heights of 0.5 to 1.9 km were imaged in a single observation by Mars Orbiter Mission in martian southern hemisphere.
Mission members monitoring the Spirit rover 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 rover, and dust devils had also been suspected as the cause.
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. 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.
Ash devils form similar to dust devils and are often seen on unstable days in burn scar areas of recent fires.
Steam devils are phenomena often observed in the steam rising from power plants.
The same conditions can produce a snow whirlwind, although differential heating is more difficult in snow-covered areas.
Coal devils are common at the coal town of Tsagaan Khad in South Gobi Province, Mongolia. They occur when dust devils pick up large amounts of stockpiled coal. Their dark color makes them resemble some tornados.
In meteorology, a cyclone is a large scale air mass that rotates around a strong center of low atmospheric pressure. Cyclones are characterized by inward spiraling winds that rotate about a zone of low pressure. The largest low-pressure systems are polar vortices and extratropical cyclones of the largest scale. Warm-core cyclones such as tropical cyclones and subtropical cyclones also lie within the synoptic scale. Mesocyclones, tornadoes and dust devils lie within smaller mesoscale. Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base of the tropical upper tropospheric trough during the summer months in the Northern Hemisphere. Cyclones have also been seen on extraterrestrial planets, such as Mars and Neptune. Cyclogenesis is the process of cyclone formation and intensification. Extratropical cyclones begin as waves in large regions of enhanced mid-latitude temperature contrasts called baroclinic zones. These zones contract and form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, extratropical cyclones occlude as cold air masses undercut the warmer air and become cold core systems. A cyclone's track is guided over the course of its 2 to 6 day life cycle by the steering flow of the subtropical jet stream.
A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are sometimes called thundershowers. Thunderstorms occur in a type of cloud known as a cumulonimbus. They are usually accompanied by strong winds, and often produce heavy rain and sometimes snow, sleet, or hail, but some thunderstorms produce little precipitation or no precipitation at all. Thunderstorms may line up in a series or become a rainband, known as a squall line. Strong or severe thunderstorms include some of the most dangerous weather phenomena, including large hail, strong winds, and tornadoes. Some of the most persistent severe thunderstorms, known as supercells, rotate as do cyclones. While most thunderstorms move with the mean wind flow through the layer of the troposphere that they occupy, vertical wind shear sometimes causes a deviation in their course at a right angle to the wind shear direction.
A thermal column is a column of rising air in the lower altitudes of Earth's atmosphere, a form of atmospheric updraft. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example of convection, specifically atmospheric convection. The Sun warms the ground, which in turn warms the air directly above it.
A multiple-vortex tornado is a tornado that contains several vortices rotating around, inside of, and as part of the main vortex. The only times multiple vortices may be visible are when the tornado is first forming or when condensation and debris are balanced such that subvortices are apparent without being obscured. They can add over 100 mph to the ground-relative wind in a tornado circulation, and are responsible for most cases where narrow arcs of extreme destruction lie right next to weak damage within tornado paths.
A gustnado is a short-lived, shallow surface-based vortex which forms within the downburst emanating from a thunderstorm. The name is a portmanteau by elision of "gust front tornado", as gustnadoes form due to non-tornadic straight-line wind features in the downdraft (outflow), specifically within the gust front of strong thunderstorms. Gustnadoes tend to be noticed when the vortices loft sufficient debris or form condensation cloud to be visible although it is the wind that makes the gustnado, similarly to tornadoes. As these eddies very rarely connect from the surface to the cloud base, they are very rarely considered as tornadoes. The gustnado has little in common with tornadoes structurally or dynamically in regard to vertical development, intensity, longevity, or formative process --as classic tornadoes are associated with mesocyclones within the inflow (updraft) of the storm, not the outflow.
A fire whirl, also commonly known as a fire devil, or, as a fire tornado, firenado, fire swirl, or fire twister, is a whirlwind induced by a fire and often composed of flame or ash. These start with a whirl of wind, often made visible by smoke, and may occur when intense rising heat and turbulent wind conditions combine to form whirling eddies of air. These eddies can contract a tornado-like vortex that sucks in debris and combustible gases.
The concept of a vortex engine or atmospheric vortex engine (AVE), independently proposed by Norman Louat and Louis M. Michaud, aims to replace large physical chimneys with a vortex of air created by a shorter, less-expensive structure. The AVE induces ground-level vorticity, resulting in a vortex similar to a naturally occurring landspout or waterspout.
A landspout is a term created by atmospheric scientist Howard B. Bluestein in 1985 for a kind of tornado not associated with a mesocyclone. The Glossary of Meteorology defines a landspout as
Tornadogenesis is the process by which a tornado forms. There are many types of tornadoes and these vary in methods of formation. Despite ongoing scientific study and high-profile research projects such as VORTEX, tornadogenesis is a volatile process and the intricacies of many of the mechanisms of tornado formation are still poorly understood.
The climate of the planet Mars has been a topic of scientific curiosity for centuries, in part because it is the only terrestrial planet whose surface can be directly observed in detail from the Earth with help from a telescope.
Atmospheric convection is the result of a parcel-environment instability, or temperature difference layer in the atmosphere. Different lapse rates within dry and moist air masses lead to instability. Mixing of air during the day which expands the height of the planetary boundary layer leads to increased winds, cumulus cloud development, and decreased surface dew points. Moist convection leads to thunderstorm development, which is often responsible for severe weather throughout the world. Special threats from thunderstorms include hail, downbursts, and tornadoes.
Atmospheric instability is a condition where the Earth's atmosphere is generally considered to be unstable and as a result the weather is subjected to a high degree of variability through distance and time. Atmospheric stability is a measure of the atmosphere's tendency to discourage or deter vertical motion, and vertical motion is directly correlated to different types of weather systems and their severity. In unstable conditions, a lifted thing, such as a parcel of air will be warmer than the surrounding air at altitude. Because it is warmer, it is less dense and is prone to further ascent.
Many areas on Mars experience the passage of giant dust devils. These dust devils leave tracks on the surface of Mars because they disturb a thin coating of fine bright dust that covers most of the Martian surface. When a dust devil goes by it blows away the coating and exposes the underlying dark surface. Within a few weeks, the dark track assumes its former bright colour, either by being re-covered through wind action or due to surface oxidation through exposure to sunlight and the Martian atmosphere.
Mesovortices are small scale rotational features found in convective storms, such as those found in bow echos, supercell thunderstorms, and the eyewall of tropical cyclones. They range in size from tens of miles in diameter to a mile or less, and can be immensely intense.
A steam devil is a small, weak whirlwind over water that has drawn fog into the vortex, thus rendering it visible.
The following is a glossary of tornado terms. It includes scientific as well as selected informal terminology.
This glossary of meteorology is a list of terms and concepts relevant to meteorology and the atmospheric sciences, their sub-disciplines, and related fields.
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