For decades, the plume in this "Hiroshima strike" photo was misidentified as themushroom cloud (itself a type of cumulonimbus flammagenitus) from theatomic bomb blast on 6 August 1945.[1][2] However, due to its much greater height, the cloud was identified in March 2016 as the cumulonimbus flammagenitus cloud produced above the city[2] by the subsequentfirestorm, which reached its peak intensity some three hours after the explosion.[3]Picture of a cumulonimbus flammagenitus cloud, taken from a commercial airliner cruising at about 10 km altitude.[4]A satellite image of the formation of a cumulonimbus flammagenitus over Argentina in 2018.
Thecumulonimbus flammagenitus cloud (CbFg), also known as thepyrocumulonimbus cloud, is a type ofcumulonimbus cloud that forms above a source of heat, such as awildfire, nuclear explosion, or volcanic eruption,[5] and may sometimes even extinguish the fire that formed it.[6] It is the most extreme manifestation of aflammagenitus cloud. According to theAmerican 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."[7]
Analogous to the meteorological distinction betweencumulus andcumulonimbus, the CbFg is a fire-aided or caused convective cloud, like a flammagenitus, but with considerable vertical development. The CbFg reaches the uppertroposphere or even lowerstratosphere and may involveprecipitation (although usually light),[8]hail, lightning, extreme low-levelwinds, and in some cases eventornadoes.[9] The combined effects of these phenomena can cause greatly increased fire-spread and cause direct dangers on the ground in addition to 'normal' fires.[9][10]
The CbFg was first recorded in relation to fire following the discovery in 1998[8] that extreme manifestations of this pyroconvection caused direct injection of large abundances of smoke from afirestorm into the lower stratosphere.[11][12][13][14][15] Theaerosol of smoke comprising CbFg clouds can persist for weeks, and with that, reduceground level sunlight in the same manner as the “nuclear winter" effect.[9][16]
In 2002, various sensing instruments detected 17 distinct CbFg in North America alone.[17]
On August 8, 2019, an aircraft was flown through a pyrocumulonimbus cloud nearSpokane, Washington, to better study and understand the composition of the smoke particles as well as get a better look at what causes these clouds to form, plus see what kinds of effects it has on the environment and air quality. It was one of the most detailed flights through CbFg to date.[18]
In 2021 alone, an estimated 83 cumulonimbus flammagenitus had formed.[19]
Alternative names and World Meteorological Organization terminology
Alternate spellings and abbreviations for cumulonimbus flammagenitus that may be found in the literature include Cb-Fg, pyrocumulonimbus, pyro-cumulonimbus, pyroCb, pyro-Cb, pyrocb, and volcanic cb, having developed amongst different specialist groups[8][20] In the media and in public communications, fire-driven examples are often referred to as fires 'making their own weather'.[21]
TheWorld Meteorological Organization does not recognize the CbFg as a distinct cloud type, but instead classifies it simply as the cumulonimbus form of the flammagenitus cloud,[22] and uses Latin as the root language for cloud names ('pyro' is of Greek origin). This was formalised in the 2017 update to theWMO International Cloud Atlas,[23] which states that any Cumulonimbus that is clearly observed to have originated as a consequence of localised natural heat sources will be classified by any appropriatespecies,variety andsupplementary feature, followed byflammagenitus.[5]
On 6 August 1945, an intense cumulonimbus-like cloud was photographed above Hiroshima, long after the cloudgenerated by the atomic bomb had dissipated. The cloud was a result of the firestorm that had by then engulfed the city.[2] Some 70,000–80,000 people, around 30% of the population of Hiroshima at the time, were killed by the blast and resultant firestorm.[citation needed]
Volcanic eruption plumes are not generally treated as CbFg, although they are convectively driven to a large extent[24] and for weaker eruptions may be significantly enhanced in height in convectively unstable environments.[25] However, for some months after theclimactic eruption ofMt Pinatubo in the Philippines in 1991, meteorological observers from the US military observed what they termed 'volcanic thunderstorms' forming near the summit: cumulus cloud complexes formed near the top of the buoyant ash plume, and frequently developed into cumulonimbus clouds (thunderstorms).[26]
The thunderstorms often drifted away from their source region at the top of the plume, producing sometimes significant amounts of localized rainfall, "mudfall," and ash fall. They also noted that thunderstorms formed over hot flows and secondary explosions even in the absence of any eruption.[27] Further investigations confirmed that the volcano had clearly enhanced the convective environment, causing thunderstorms to form on average earlier in the day and more reliably than in surrounding areas, and that the presence of volcanic ash in cloud tops in the upper troposphere could be inferred from satellite imagery in at least one case.[20]
On 18 January 2003, a series of CbFg clouds formed from a severe wildfire, during the2003 Canberra bushfires in Canberra, Australia.[9] This resulted in a largefire tornado, rated F3 on theFujita scale: the first confirmed violent fire tornado.[28][29] The tornado and associated fire killed 4 people and injured 492.
On 7 February 2009, theBlack Saturday bushfires killed 173 people, destroyed over 2000 homes, burnt more than 450,000 ha, and resulted in losses of over four billion Australian dollars in Victoria, Australia. Multiple fire plumes produced a number of distinct CbFg, some of which reached heights of 15 km on that day and generated a large amount of lightning.[30]
On 30 December 2019, two fire response vehicles were overturned by what was described as a 'fire tornado' originating from an active cumulonimbus flammagenitus cloud near Jingellic, New South Wales, Australia, on a day when multiple CbFg were recorded in the neighbouring State of Victoria to an altitude of at least 16 km.[31] One of these vehicles was variously described as weighing between 8 and 12 tonnes.[10][32] The incident resulted in one fatality and injuries to two others.
Animation of the formation of a pyrocumulonimbus above the 2020 Creek Fire in California
On 4 September 2020, theCreek Fire began in theBig Creek drainage area between Shaver Lake andHuntington Lake, California. By 8 September 2020, the fire was among the 20 largest wildfires ever seen in California, with an area of 152,833 acres burnt and 0% containment.[33] The rapidly growing wildfire, aided by hot, windy, and dry weather, drought, and beetle-killed timber, created a pyrocumulonimbus cloud. According to NASA, it is the largest such cloud ever seen in the United States.[34]
Widespread cumulonimbus flammagenitus appeared over British Columbia and northwestern Alberta in connection with the2021 British Columbia wildfires, many of which were exacerbated by the historic2021 Western North America heat wave. In just 15 hours, between 3pm June 30 and 6am July 1, 710,117 lightning strikes were recorded, of which 112,803 were cloud-to-ground strokes.[35]
This activity followed several days of unprecedented temperature highs in late June, including Canada's highest-ever recorded temperature of 49.6°C inLytton, British Columbia (also known asCamchin or ƛ'q'əmcín[36]).[37] At least 19 wildfires ignited between June 27 and 29, but most remained under 5 hectares (12 acres);[38] one fire, however, grew to at least 2 km2 (0.77 sq mi) by June 29, prompting evacuations.[38] On June 30, two large fires spread out of control, one nearKamloops Lake which grew to 200 km2 (77 sq mi) by evening, and the other north ofLillooet, which similarly grew to tens of square kilometres that day.[39][40] at least two residents were unable to escape due to the speed of the firestorm's advance and perished when a utility pole was blown down on them by flames.[41]
During theBootleg Fire in Oregon in July 2021, an NWS forecaster told theNew York Times that the fire had createdpyrocumulus clouds almost daily, with some reaching as high as 30,000 feet; the fire also caused a pyrocumulonimbus cloud to form nearly 45,000 feet high, bringing lightning and rain.[42]
^abTupper, Andrew; Oswalt, J. Scott; Rosenfeld, Daniel (2005). "Satellite and radar analysis of the volcanic-cumulonimbi at Mount Pinatubo, Philippines, 1991".Journal of Geophysical Research: Atmospheres.110 (D9): D09204.Bibcode:2005JGRD..110.9204T.doi:10.1029/2004JD005499.ISSN2156-2202.
^Sparks, R. S. J. (Robert Stephen John), 1949- (1997).Volcanic plumes. Wiley.OCLC647419756.{{cite book}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link)
^Tupper, Andrew; Textor, Christiane; Herzog, Michael; Graf, Hans-F.; Richards, Michael S. (2009-11-01). "Tall clouds from small eruptions: the sensitivity of eruption height and fine ash content to tropospheric instability".Natural Hazards.51 (2):375–401.Bibcode:2009NatHa..51..375T.doi:10.1007/s11069-009-9433-9.ISSN1573-0840.S2CID140572298.
^"Creek Fire". California Department of Forestry and Fire Protection. 8 September 2020.Archived from the original on 7 September 2020. Retrieved8 September 2020.
