Willow Fire AZ 7 8 2004 SE burnout 035-001

A flammagenitus cloud, also known as a flammagenitus, pyrocumulus cloud, or fire cloud, is a dense

cumuliform cloud Cumulus clouds are clouds which have flat bases and are often described as "puffy", "cotton-like" or "fluffy" in appearance. Their name derives from the Latin ''cumulo-'', meaning ''heap'' or ''pile''. Cumulus clouds are low-level clouds, gene ...

associated with fire or volcanic eruptions. A flammagenitus is similar dynamically in some ways to a

firestorm 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 ...

, and the two phenomena may occur in conjunction with each other. However, either may occur without the other.

Formation

A flammagenitus cloud is produced by the intense

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

ing of the

air The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...

from the surface. The intense heat induces

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the c ...

, which causes the air mass to rise to a point of stability, usually in the presence of

moisture Moisture is the presence of a liquid, especially water, often in trace amounts. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some commercial products. Moisture also refers to the amount of water vapo ...

. Phenomena such as

volcanic eruption Several types of volcanic eruptions—during which lava, tephra (ash, lapilli, volcanic bombs and volcanic blocks), and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are oft ...

s and

forest fires A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identif ...

can induce formation of this cloud, by mechanisms similar to those that form homogenitus clouds. The presence of a low-level

jet stream Jet streams are fast flowing, narrow, meandering air currents in the atmospheres of some planets, including Earth. On Earth, the main jet streams are located near the altitude of the tropopause and are westerly winds (flowing west to east) ...

can enhance its formation. Condensation of ambient moisture (moisture already present in the atmosphere), as well as moisture evaporated from burnt vegetation or volcanic

outgassing Outgassing (sometimes called offgassing, particularly when in reference to indoor air quality) is the release of a gas that was dissolved, trapped, frozen, or absorbed in some material. Outgassing can include sublimation and evaporation (which ...

(water vapour being a dominant component of volcanic eruptive gases), occurs readily on particles of ash. Pyrocumulus cloud Tiger Fire

Flammageniti contain severe turbulence, manifesting as strong gusts at the surface, which can exacerbate a large conflagration. A large flammagenitus, particularly one associated with a volcanic eruption, may also produce

lightning Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an average ...

. This is a process not yet fully understood, but is probably in some way associated with charge separation induced by severe turbulence, and, perhaps, by the nature of the particles of ash in the cloud. Large flammageniti can contain temperatures well below freezing, and the electrostatic properties of any ice that forms may also play a role. A flammagenitus that produces lightning is actually a type of

cumulonimbus Cumulonimbus (from Latin ''cumulus'', "heaped" and ''nimbus'', "rainstorm") is a dense, towering vertical cloud, typically forming from water vapor condensing in the lower troposphere that builds upward carried by powerful buoyant air currents. ...

, a thundercloud, and is called

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 tha ...

. The World Meteorological Organization formerly classified flammagenitus and cumulonimbus flammagenitus respectively as

cumulus Cumulus clouds are clouds which have flat bases and are often described as "puffy", "cotton-like" or "fluffy" in appearance. Their name derives from the Latin ''cumulo-'', meaning ''heap'' or ''pile''. Cumulus clouds are low-level clouds, gener ...

(mediocris or congestus) and cumulonimbus. In 2017, the WMO

International Cloud Atlas The ''International Cloud Atlas'' or simply the ''Cloud Atlas'', is a cloud atlas that was first published in 1896 and has remained in print since. Its initial purposes included aiding the training of meteorologists and promoting more consisten ...

chose flammagenitus as the formal name of these clouds.

Appearance

Wildfire in Yellowstone NP produces Pyrocumulus cloud

Pyrocumulus cloud, Beaver complex fire 2014

Flammagenitus is often grayish to brown in color because of the ash and

smoke Smoke is a suspension of airborne particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-produc ...

associated with the fire. It also tends to expand because the ash involved in the cloud's formation increases the amount of

condensation nuclei Cloud condensation nuclei (CCNs), also known as cloud seeds, are small particles typically 0.2 µm, or one hundredth the size of a cloud droplet. CCNs are a unique subset of aerosols in the atmosphere on which water vapour condenses. This ...

. This poses a problem, as the cloud can trigger a

thunderstorm A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are some ...

, from which the lightning can start another fire. Wildfire in Yellowstone National Park produces Pyrocumulus clouds1

Effects on wildfires

A flammagenitus cloud can help or hinder a fire. Sometimes, the moisture from the air condenses in the cloud and falls as rain, often extinguishing the fire. There have been numerous examples of a large firestorm being extinguished by the flammagenitus that it created. However, if the fire is large enough, the cloud may continue to grow, and become a type of

cumulonimbus cloud Cumulonimbus (from Latin ''cumulus'', "heaped" and ''nimbus'', "rainstorm") is a dense, towering vertical cloud, typically forming from water vapor condensing in the lower troposphere that builds upward carried by powerful buoyant air currents. ...

known as a

, which may produce lightning and start another fire. Even if there is no lightning, a cloud of this type can cause a sudden increase in wind speed, which could dramatically worsen the wildfire that created the cloud.

References

External links

* {{Cloud types Cumulus Wildfire ecology Wildfires Volcanism