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,[5] and may sometimes even extinguish the fire that formed it.[6] 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."[7]

A satellite image of the formation of a cumulonimbus flammagenitus over Argentina in 2018.
For decades, the plume in this "Hiroshima strike" photo was misidentified as the mushroom cloud (itself a type of cumulonimbus flammagenitus) from the atomic 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 subsequent firestorm, 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]

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 (although usually light),[8] hail, lightning, extreme low-level winds, and in some cases even tornadoes.[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 a firestorm into the lower stratosphere.[11][12][13][14][15][16] The aerosol of smoke comprising CbFg clouds can persist for weeks, and with that, reduce ground level sunlight in the same manner as the “nuclear winter" effect.[9][17]

In 2002, various sensing instruments detected 17 distinct CbFg in North America alone.[18]

On August 8, 2019, an aircraft was flown through a Pyrocumulonimbus cloud near Spokane, 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.[19]

In 2021 alone, an estimated 83 Cumulonimbus flammagenitus had formed. [20]

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