User:Penitentes/Fire tornado (draft)

A fire tornado, sometimes also called a fire-generated tornadic vortex (FGTV) or a pyrotornado, is a vortex generated by a fire that reaches the scale and strength of a traditional tornado. Fire tornadoes are one of many kinds of vortices that appear in fires, varying in size...

Few confirmed examples exist, all of them occurring in the 21st century. The mechanism that leads to their formation are not entirely understood, but research suggests they have roots in both fire and cloud processes, making them distinct from both fire whirls (common in wildfires) and traditional tornadoes, which typically form via the mesocyclone of a supercell thunderstorm.

Pyro-tornadogenesis was first scientifically identified following a destructive vortex that formed during a bushfire on the outskirts of Canberra, Australia, in 2003. The vortex was filmed by multiple bystanders at a distance but was not generally accepted as a genuine fire-generated tornado until 2012. Several other examples have been recognized since.

Definitions
The scientific literature contains multiple names for the phenomenon, including "pyrogenetic tornado", "fire-generated tornadic vortex (FGTV)", and "pyrotornado".

According to the American Meteorological Society's glossary of meteorology, a tornado is defined as "a rapidly rotating column of air extending vertically from the surface to the base of a cumuliform cloud."

The terms fire whirl and fire tornado have often been used interchangeably to describe a vortex of any size or duration occurring in a wildfire. Only in recent years have scientists begun to distinguish types of vortices from one another, in particular highlighting the rare cases of actual pyro-tornadogenesis (or tornado formation during/due to a wildfire).

One of the first formal attempts at creating a rigid nomenclature for vortices in fires was in a National Oceanic and Atmospheric Administration (NOAA) technical memorandum from 1978, where National Weather Service (NWS) meteorologist David W. Goens separated fire whirls into four general classes: fire devils (typically 3 to 33 feet in diameter with rotational velocities less than 22 mph), fire whirls (typically 33 to 100 feet, with rotational velocities of 22 to 67 mph), fire tornadoes (typically 100 to 1,000 feet in diameter with rotational velocities up to 90 MPH), and fire storms (1,000 to 10,000 feet in diameter with winds estimated in excess of 110 mph). Goens' classification did not enter general usage, but attempts have been made in more recent years to suggest a consistent classification scheme.

Formation
Fire whirls and fire tornadoes both necessarily begin with a fire, the combustion from which heats the atmosphere above it. As that hot air warms it rises, forming a strong updraft. Updrafts as strong as 130 miles per hour have been found in pyrocumulonimbus clouds, equaling the strength of those found in tornado-producing supercell thunderstorms. The rising hot air is replaced at its base by cooler air, which generates a horizontal inflow jet, or winds converging from all directions towards the fire and the base of the primary updraft.

The second ingredient is the presence of wind shear, or air is flowing in different directions adjacent to the inflow winds. The wind shear provides the initial source of rotation. This rotation inhibits the dilution and mixing of air, allowing the column of rising air to act in a chimney-like fashion, strengthening the updraft, inflow winds, and surface combustion.

These are the basic underlying processes behind the development of all fire-related whirlwinds. Where fire tornadoes diverge from smaller and briefer fire whirls is in their development of a connection to a pyrocumulonimbus cloud. A pyrocumulonimbus cloud is a fire-generated thunderstorm, formed when the water vapor contained in the rising updraft and associated smoke plume rises high enough into the atmosphere to condense into liquid cloud droplets, forming distinctive bright white clouds. The process of condensation releases heat back into the atmosphere (called latent heat release). This is the same process that fuels an ordinary thunderstorm. Wildfires have long been known to be capable of generating severe convective storms, which in addition to the strong updrafts can also produce lightning and hail, though typically not precipitation. The precise manner of the link between fire tornadoes and pyro-convection is unclear. It is currently hypothesized by researchers that the latent heat release in rapid pyrocumulonimbus development reinvigorates the updraft, and the heat release and updraft stretches the column and concentrates its pre-existing rotation (or 'vorticity') in the lower atmosphere, causing it to accelerate in much the same way a figure skater does when they pull their arms in. The involvement of the pyrocumulonimbus cloud in the development of fire tornadoes is what distinguishes those vortices from smaller-scale fire vortices, which concentrate their rotation solely through fire-related processes.

Need to describe CVPs, too:

"Like water flowing around a boulder in a stream, he found, wind is forced to split around the plume of superheated air and ash rising off a wildfire. And just like water flowing around a boulder, “these two eddies develop,” said Lareau, “which we call counterrotating vortices [CRVs]. Between those CRVs there’s this kind of wake—air moving back toward the fire in opposition to what the wind would be doing if the fire wasn’t there.”" from Eos article

Embedded and shedding vortices
University of Nevada Reno scientist Neil P. Lareau and others published a research paper in 2022 that studied fire-generated tornadic vortices in the 2020 Loyalton, Creek, and Bear fires in California. The paper identified two distinct morphologies: some vortices remained embedded within the main fire, and some that detached from the main fire and traveled 'downstream' while remaining pendant from the leaning smoke plume.

Impacts and hazards
Fire tornadoes are associated with pyrocumulonimbus clouds and their attendant hazards, including cloud-to-ground lightning strikes, extreme darkness as the cloud nullifies solar radiation, ember showers, and winds.

In Australia, following the 2012 scientific confirmation of the 2003 tornado, the Australian Capital Territory Emergency Services Agency (ACT ESA) intended to raise the issue of fire tornado impacts with the Standards Australia Wind Loadings Committee and the Australian Buildings Code Board. Building codes there specified structural engineering requirements for cyclonic winds, but not for tornadic winds. The Carr Fire tornado killed a firefighter, collapsed electrical power transmission towers, and caused other damage on the outskirts of a metropolitan area. [Scientific papers argue they pose a hazard?]

https://www.ncdc.noaa.gov/stormevents/eventdetails.jsp?id=774718

The Carr Fire tornado was estimated to have a peak gas temperature of 2,700 degrees F.

Detection and warning
Fire tornadoes can be detected in much the same manner as regular tornadoes, including the use of Doppler weather radar systems to detect rotation aloft. In the United States, where several fire tornadoes have occurred, some of them have been surveyed by National Weather Service meteorologists and their resulting damage given ratings on the Enhanced Fujita scale, as in a typical tornado damage survey—the first being the Carr Fire tornado.

However, the National Weather Service does not yet have a unified standard for warnings for fire tornadoes: as of 2020, the NWS had not issued specific policy guidance to its 122 forecast offices. Decisions are made on a case-by-case basis by the agency's constituent weather forecast offices (WFOs), with some offices concluding internally that they will not issue tornado warnings for fire tornadoes: one meteorologist with the National Weather Service office in Hanford argued that "We need to get the science down before we start building policy about when we alert the public about such things. We don’t want to overburden emergency services or the public with limited science."

During the Loyalton Fire, staff at the National Weather Service office in Reno identified rotation within the smoke plume and chose to issue a modified tornado warning for a possible "fire-induced tornado", the first of its kind. Staff there had the advantage of a favorable location for radar detection and prior conversations about what to do in a fire tornado scenario, based on the experience of an incident meteorologist who had previously been assigned to the Carr Fire. Several weeks later, during the Creek Fire, the NWS office in Hanford considered—but ultimately decided against—issuing a tornado warning. A warning coordination meteorologist there said the decision was made because they feared making people conflicted about whether to shelter from the tornado or evacuate from the wildfire.

List of confirmed fire tornadoes
The following are confirmed examples of fire tornadoes.