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

A fire whirl, also commonly known as a fire devil, 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.

Contents

The phenomenon is sometimes mislabelled a fire tornado, firenado, fire swirl, or fire twister, but these are a separate phenomenon where a fire has such intensity that it generates an actual tornado. (This phenomenon was first verified in the 2003 Canberra bushfires.) Fire whirls 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. [1]

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 fire whirls have been generated by very small fires in laboratories. [3]

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]

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.

Fire whirls 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]

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

A flame-filled fire whirl Fire-whirl.jpg
A 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 pyrocumulonimbus clouds 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, 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.

Supercell thunderstorm that is characterized by the presence of a mesocyclone

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.

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 bombings of Hiroshima and Nagasaki.

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 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.

Tornado records

This article lists various tornado records. The most "extreme" tornado in recorded history was the Tri-State Tornado, which spread through parts of Missouri, Illinois, and Indiana on March 18, 1925. It is considered an F5 on the Fujita Scale, even though tornadoes were not ranked on any scale at the time. It holds records for longest path length at 219 miles (352 km), longest duration at about 3½ hours, and fastest forward speed for a significant tornado at 73 mph (117 km/h) anywhere on Earth. In addition, it is the deadliest single tornado in United States history with 695 fatalities. It was also the third-costliest tornado in history at the time, but has been surpassed by several others non-normalized. When costs are normalized for wealth and inflation, it still ranks third today.

Waterspout weather phenomenon, intense columnar vortex that occurs over a body of water, commonly a non-supercell tornado over water

A waterspout is an intense columnar vortex that occurs over a body of water. Some are connected to a cumulus congestus cloud, some to a cumuliform cloud and some to a cumulonimbus cloud. In the common form, it is a non-supercell tornado over water.

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.

Funnel cloud funnel-shaped cloud of condensed water droplets, associated with a rotating column of wind

A funnel cloud is a funnel-shaped cloud of condensed water droplets, associated with a rotating column of wind and extending from the base of a cloud but not reaching the ground or a water surface. A funnel cloud is usually visible as a cone-shaped or needle like protuberance from the main cloud base. Funnel clouds form most frequently in association with supercell thunderstorms. Funnel clouds are visual phenomena, these are not the vortex of wind itself.

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, as either companion/satellite tornadoes or nonmesocyclonic tornadoes.

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

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

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.

Cumulonimbus flammagenitus

The cumulonimbus flammagenitus cloud (CbFg), also known as the pyrocumulonimbus cloud, is a type of cumulonimbus cloud that forms above a source of heat, such as a wildfire or volcanic eruption, 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 CbFg 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. The combined effects of these phenomena can cause greatly increased fire-spread and cause direct dangers on the ground in addition to 'normal' fires.

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.

Rear flank downdraft

The rear flank downdraft or RFD is a region of dry air wrapping around the back of a mesocyclone in a supercell thunderstorm. These areas of descending air are thought to be essential in the production of many supercellular tornadoes. Large hail within the rear flank downdraft often shows up brightly as a hook on weather radar images, producing the characteristic hook echo, which often indicates the presence of a tornado.

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.

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

Satellite tornado smaller tornado that orbits around a larger "parent" tornado

A satellite tornado is a tornado that revolves 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.

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