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Fire whirl

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A fire whirl with flames in the vortex

A 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 made up of flame or ash. They usually start with a whirl of wind or smoke, and may occur when intense rising heat and turbulent wind conditions combine to form whirling eddies of air. These eddies can contract into a tornado-like vortex that sucks in burning debris and combustible gases.

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, even those fire whirls are not classic tornadoes, in that their vorticity derives from surface winds and heat-induced lifting, rather than a tornadic mesocyclone aloft.

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).[1] Often, fire whirls are created when a wildfire or firestorm creates its own wind, which can turn into a vortex of fire. This causes the tall and skinny appearance of a fire whirl's core.

Most of the largest fire whirls are spawned from wildfires. They form when a warm updraft and convergence from the wildfire are present.[2] They are usually 10–50 meters tall, a few meters wide, and last only a few minutes. However, some can be more than a kilometer tall, contain winds over 160 km/h, and persist for more than 20 minutes.[3]

Fire whirls can uproot trees up to 15 metres (49 ft) tall.[4] 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.

Examples

Another 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.[5]

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 kilometers away.[6]

On 18 January 2003, a supercell thunderstorm formed from a cumulonimbus flammagenitus cloud[citation needed] associated with a severe wildfire, during the 2003 Canberra bushfires in Canberra, Australia. The supercell resulted in a large fire tornado, rated at EF3 on the Fujita scale, the first confirmed violent fire tornado.[7][8] The tornado and associated fire killed 4 people and injured 492.

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 metres (330 ft) high.[9]

Residents in the city of Redding, California, while evacuating the area from the massive Carr Fire in late July 2018, reported seeing pyrocumulonimbus[citation needed] 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 2nd, 2018, a preliminary damage survey, led by the National Weather Service in Sacramento, California, rated the July 26th fire whirl as an EF3 tornado with winds in excess of 143 mph.[10]

Classification

There are currently three known types of fire whirls:[11]

  • Type 1: Stable and centered over burning area.
  • Type 2: Stable or transient, downwind of burning area.
  • Type 3: Steady or transient, centered over an open area adjacent to an asymmetric burning area with wind.

There is evidence suggesting that the fire whirl in the Hifukusho-ato area, during the 1923 Great Kantō earthquake, was of type 3.[12]

References

Notes

  1. ^ Fortofer, Jason (20 September 2012) "New Fire Tornado Spotted in Australia" National Geographic
  2. ^ Umscheid, Michael E.; Monteverdi, J.P.; Davies, J.M. (2006). "Photographs and Analysis of an Unusually Large and Long-lived Firewhirl". Electronic Journal of Severe Storms Meteorology. 1 (2).
  3. ^ Grazulis, Thomas P. (July 1993). Significant Tornadoes 1680–1991: A Chronology and Analysis of Events. St. Johnsbury, VT: The Tornado Project of Environmental Films. ISBN 1-879362-03-1.
  4. ^ Billing, P., ed. (June 1983). Otways Fire No. 22 – 1982/83 Aspects of fire behaviour. Research Report No.20 (PDF). Victoria Department of Sustainability and Environment. Retrieved 2012-12-19.
  5. ^ Quintiere, James G. (1998). Principles of Fire Behavior. Thomson Delmar Learning. ISBN 0-8273-7732-0.
  6. ^ Hissong, J. E. (1926). "Whirlwinds At Oil-Tank Fire, San Luis Obispo, Calif". Mon. Wea. Rev. 54 (4): 161–3. Bibcode:1926MWRv...54..161H. doi:10.1175/1520-0493(1926)54<161:WAOFSL>2.0.CO;2.
  7. ^ Anja Taylor (6 June 2013). "Fire Tornado". Australian Broadcasting Corporation. Retrieved 6 June 2013.
  8. ^ McRae, R; Sharpies, J; Wilkies, S; Walker, A (12 October 2012). "An Australian pyro-tornadogenesis event". Nat Hazards. 65 (3): 1801. doi:10.1007/s11069-012-0443-7. Retrieved 4 September 2016.
  9. ^ van Beynen, Martin (11 March 2017). "Firestorm". The Press. pp. C1–C4. Retrieved 12 March 2017.
  10. ^ "NWS Sacramento on Twitter". Twitter. Retrieved 2018-08-02.
  11. ^ Williams, Forman (22 May 2009). "The Occurrence and Mechanisms of Fire Whirls" (PDF). La Lolla, California; Valladolid, Spain: MAE UCSD; Spanish Section of the Combustion Institute. Archived from the original (PDF) on 13 May 2014.
  12. ^ Kuwana, Kazunori; Kozo Sekimoto; Kozo Saito; Forman A. Williams (May 2008). "Scaling fire whirls". Fire Safety Journal. 43 (4): 252–7. doi:10.1016/j.firesaf.2007.10.006.

Bibliography

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