Fire whirl

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Fire whirl
Fire whirl (FWS) crop.jpg
A fire whirl with flames in the vortex
Area of occurrenceWorldwide (most frequent in areas subject to wildfires)
SeasonAll year (most frequent in dry season)
EffectWind damage, burning, propagation/intensification of fires

fire whirl, also commonly known as a fire devil, or, (in many cases erroneously) as a fire tornado, firenado, fire swirl, or fire twister, is a whirlwind induced by a fire and often (at least partially) 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.

Whirlwind weather phenomenon

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.

Fire rapid oxidation of a material

Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition.

Flame visible, gaseous part of a fire

A flame is the visible, gaseous part of a fire. It is caused by a highly exothermic reaction taking place in a thin zone. Very hot flames are hot enough to have ionized gaseous components of sufficient density to be considered plasma.

Contents

Fire whirls are sometimes colloquially called fire tornadoes, but are not usually classifiable as tornadoes as the vortex in most cases does not extend from the surface to cloud base. Also, even in such cases, those fire whirls very rarely are classic tornadoes, as their vorticity derives from surface winds and heat-induced lifting, rather than from a tornadic mesocyclone aloft, although a handful of suspected cases of the latter are known. [1]

In continuum mechanics, the vorticity is a pseudovector field that describes the local spinning motion of a continuum near some point, as would be seen by an observer located at that point and traveling along with the flow.

Wind Flow of gases or air on a large scale

Wind is the flow of gases on a large scale. On the surface of the Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the Sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space. Winds are commonly classified by their spatial scale, their speed, the types of forces that cause them, the regions in which they occur, and their effect. The strongest observed winds on a planet in the Solar System occur on Neptune and Saturn. Winds have various aspects, an important one being its velocity ; another the density of the gas involved; another its energy content or wind energy. Wind is also a great source of transportation for seeds and small birds; with time things can travel thousands of miles in the wind.

Mesocyclone

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.

Formation

A fire whirl consists of a burning core and a rotating pocket of air. A fire whirl can reach up to 2,000 °F (1,090 °C). [2] Fire whirls become frequent when a wildfire, or especially firestorm, creates its own wind, which can spawn large vortices. Even bonfires often have whirls on a smaller scale and tiny firewhirls have been generated by very small fires in laboratories. [3]

Wildfire uncontrolled fire in an area of combustible vegetation that occurs in the countryside or a wilderness area

A wildfire or wildland fire is a fire in an area of combustible vegetation occurring in rural areas. Depending on the type of vegetation present, a wildfire can also be classified more specifically as a brush fire, bushfire, desert fire, forest fire, grass fire, hill fire, peat fire, vegetation fire, or veld fire.

Firestorm conflagration which attains such intensity that it creates and sustains its own wind system

A firestorm is a conflagration which attains such intensity that it creates and sustains its own wind system. It is most commonly a natural phenomenon, created during some of the largest bushfires and wildfires. Although the term has been used to describe certain large fires, the phenomenon's determining characteristic is a fire with its own storm-force winds from every point of the compass. The Black Saturday bushfires and the Great Peshtigo Fire are possible examples of forest fires with some portion of combustion due to a firestorm, as is the Great Hinckley Fire. Firestorms have also occurred in cities, usually as a deliberate effect of targeted explosives, such as occurred as a result of the aerial firebombings of Hamburg, Dresden, firebombing of Tokyo and the atomic bombing of Hiroshima.

Bonfire controlled outdoor fire

A bonfire is a large but controlled outdoor fire, used either for informal disposal of burnable waste material or as part of a celebration.

Most of the largest fire whirls are spawned from wildfires. They form when a warm updraft and convergence from the wildfire are present. [4] They are usually 10–50 m (33–164 ft) tall, a few meters (several feet) wide, and last only a few minutes. Some, however, can be more than 1 km (0.6 mi) tall, contain wind speeds over 200 km/h (120 mph), and persist for more than 20 minutes. [5]

Wind speed

Wind speed, or wind flow velocity, is a fundamental atmospheric quantity caused by air moving from high to low pressure, usually due to changes in temperature. Note that wind direction is usually almost parallel to isobars, due to Earth's rotation.

Fire whirls can uproot trees that are 15 m (49 ft) tall or more. [6] These can also aid the 'spotting' ability of wildfires to propagate and start new fires as they lift burning materials such as tree bark. These burning embers can be blown away from the fireground by the stronger winds aloft.

Firewhirls can be common within the vicinity of a plume during a volcanic eruption. [7] [8] These range from small to large and form from a variety of mechanisms, including those akin to typical firewhirl processes, but can result in Cumulonimbus flammagenitus (cloud) spawning landspouts and waterspouts [9] or even to develop mesoyclone-like updraft rotation of the plume itself and/or of the cumulonimbi, which can spawn tornadoes similar to those in supercells. [10] Pyrocumulonimbi generated by large fires on rare occasion also develops in a similar way. [11] [1] [12] [13]

Eruption column

An eruption column is a cloud of super-heated ash and tephra suspended in gases emitted during an explosive volcanic eruption. The volcanic materials form a column that may rise many kilometers into the air above the vent of the volcano. In the most explosive eruptions, the eruption column may rise over 40 km (25 mi), penetrating the stratosphere. Stratospheric injection of aerosols by volcanoes is a major cause of short-term climate change.

Cumulonimbus flammagenitus (cloud)

The cumulonimbus flammagenitus cloud (CbFg) is a type of cumulonimbus cloud that forms above a source of heat, such as a wildfire, and may sometimes even extinguish the fire that formed it. It is the most extreme manifestation of a flammagenitus cloud. According to the American Meteorological Society’s Glossary of Meteorology, a flammagenitus is "a cumulus cloud formed by a rising thermal from a fire, or enhanced by buoyant plume emissions from an industrial combustion process." Analogous to the meteorological distinction between cumulus and cumulonimbus, the cumulonimbus flammagenitus is a fire-aided or –caused convective cloud, like a flammagenitus, but with considerable vertical development. The CbFg reaches the upper troposphere or even lower stratosphere and may involve precipitation, hail, lightning, extreme low-level winds, and in some cases even tornadoes.

Landspout slang term for a kind of tornado not associated with the mesocyclone of a thunderstorm

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

Classification

There are currently three widely recognized types of fire whirls: [14]

There is evidence suggesting that the fire whirl in the Hifukusho-ato area, during the 1923 Great Kantō earthquake, was of type 3. [15] Other mechanism and firewhirl dynamics may exist. [16]

Notable examples

Another flame-filled fire whirl Fire-whirl.jpg
Another flame-filled fire whirl

An extreme example of a fire whirl is the 1923 Great Kantō earthquake in Japan, which ignited a large city-sized firestorm and produced a gigantic fire whirl that killed 38,000 people in fifteen minutes in the Hifukusho-Ato region of Tokyo. [17]

Another example is the numerous large fire whirls (some tornadic) that developed after lightning struck an oil storage facility near San Luis Obispo, California, on 7 April 1926, several of which produced significant structural damage well away from the fire, killing two. Many whirlwinds were produced by the four-day-long firestorm coincident with conditions that produced severe thunderstorms, in which the larger fire whirls carried debris 5 km (3.1 mi) away. [18]

Firewhirls were produced in the conflagrations and firestorms triggered by firebombings of European and Japanese cities during World War Two and by the atomic bombings of Hiroshima and Nagasaki. Firewhirls associated with the bombing of Hamburg, particularly those of 27–28 July 1943, were studied. [19]

Throughout the 1960s-1970s, particularly in 1978-1979, firewhirls ranging from the transient and very small to intense, long-lived tornadic-like vortices capable of causing significant damage were spawned by fires generated from the 1000 MW Météotron, a series of large oil wells located in the Lannemezan plain of France used for testing atmospheric motions and thermodynamics. [20]

During the 2003 Canberra bushfires in Canberra, Australia a violent firewhirl was documented. It was calculated to have horizontal winds of 160 mph (260 km/h) and vertical air speed of 93 mph (150 km/h), causing the flashover of 300 acres (120 ha) in 0.04 seconds. [21] It was the first known firewhirl in Australia to have EF3 wind speeds on the Enhanced Fujita scale. [22]

A fire whirl, of reportedly uncommon size for New Zealand wildfires, formed on day three of the 2017 Port Hills fires in Christchurch. Pilots estimated the fire column to be 100 m (330 ft) high. [23]

Residents in the city of Redding, California, while evacuating the area from the massive Carr Fire in late July 2018, reported seeing pyrocumulonimbusclouds and tornado-like behaviour from the firestorm, resulting in uprooted trees, cars, structures and other wind related damages in addition to the fire itself. As of August 2, 2018, a preliminary damage survey, led by the National Weather Service (NWS) in Sacramento, California, rated the July 26th fire whirl as an EF3 tornado with winds in excess of 143 mph (230 km/h). [24]

See also

Related Research Articles

Tornado violently rotating column of air that is in contact with both the earths surface and a cumulonimbus cloud in the air

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 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.

Dust devil meteorological phenomenon of sand in air

A dust devil is a strong, well-formed, and relatively long-lived whirlwind, ranging from small to large. 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.

Ted Fujita Japanese-American severe storms researcher

Tetsuya Theodore "Ted" Fujita was a prominent Japanese-American severe storms researcher. His research at the University of Chicago on severe thunderstorms, tornadoes, hurricanes, and typhoons revolutionized the knowledge of each. Although he is probably best known for creating the Fujita scale of tornado intensity and damage., he also discovered downbursts and microbursts, and was an instrumental figure in advancing modern understanding of many severe weather phenomena and how they affect people and communities, especially through his work exploring the relationship between wind speed and damage.

Wall cloud cloud formation

A wall cloud is a large, localized, persistent, and often abrupt lowering of cloud that develops beneath the surrounding base of a cumulonimbus cloud and from which tornadoes sometimes form. It is typically beneath the rain-free base (RFB) portion of a thunderstorm, and indicates the area of the strongest updraft within a storm. Rotating wall clouds are an indication of a mesocyclone in a thunderstorm; most strong tornadoes form from these. Many wall clouds do rotate, however some do not.

Multiple-vortex tornado Tornado comprising multiple vortices

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.

Anticyclonic tornado

An anticyclonic tornado is a tornado which rotates in a clockwise direction in the Northern Hemisphere and a counterclockwise direction in the Southern Hemisphere. The term is a naming convention denoting the anomaly from normal rotation which is cyclonic in upwards of 98 percent of tornadoes. Many anticyclonic tornadoes are smaller and weaker than cyclonic tornadoes, forming from a different process.

Robert C. Miller American meteorologist and air force officer

Col. Robert C. Miller, USAF (1920–1998), was an American meteorologist, who pioneered severe convective storms forecasting and applied research, developing an empirical forecasting method, identifying many features associated with severe thunderstorms, a forecast checklist and manuals, and is known for the first official tornado forecast, and it verified, in 1948.

Tornadogenesis process by which a tornado forms

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.

Tornado family

A tornado family is a series of tornadoes spawned by the same supercell thunderstorm. These families form a line of successive or parallel tornado paths and can cover a short span or a vast distance. Tornado families are sometimes mistaken as a single continuous tornado, especially prior to the 1970s. Sometimes the tornado tracks can overlap and expert analysis is necessary to determine whether or not damage was created by a family or a single tornado. In some cases, such as the Hesston-Goessel, Kansas tornadoes of March 1990, different tornadoes of a tornado family merge, making discerning whether an event was continuous or not more difficult.

Ron Przybylinski American meteorlogist

Ronald William Przybylinski was an American meteorologist with primary areas of interest in bow echoes, mesovortices, and quasi-linear convective system (QLCS) tornadoes.

A skipping tornado is a process tornado which has a discontinuous damage path.

Satellite tornado

A satellite tornado is a tornado that rotates around a larger, primary tornado and interacts with the same mesocyclone. Satellite tornadoes occur apart from the primary tornado and are not considered subvortices; the primary tornado and satellite tornadoes are considered to be separate tornadoes. The cause of satellite tornadoes is not known. Such tornadoes are more often anticyclonic than are typical tornadoes and these pairs may be referred to as tornado couplets. Satellite tornadoes most commonly form in association with very large and intense tornadoes.

Johannes Letzmann Estonian meteorlogist

Johannes Peter Letzmann was an Estonian meteorologist, and a pioneering tornado researcher. His prolific output related to severe storms concepts included: developing tornado damage studies, atmospheric vortices, theoretical studies and laboratory simulations, tornado case studies, and observation programs. It generated extensive analysis techniques and insights on tornadoes at a time when there was still very little research on the subject in the United States.

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.

Tornado debris signature

A tornadic debris signature (TDS), often colloquially referred to as a debris ball, is an area of high reflectivity on weather radar caused by debris lofting into the air, usually associated with a tornado. A TDS may also be indicated by dual-polarization radar products, designated as a polarimetric tornado debris signature (PTDS). Polarimetric radar can discern meteorological and nonmeteorological hydrometeors and the co-location of a PTDS with the enhanced reflectivity of a debris ball are used by meteorologists as confirmation that a tornado is occurring.

References

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Further reading