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A flammagenitus cloud, also known as a flammagenitus, pyrocumulus cloud, or fire cloud, is a dense
A flammagenitus cloud is produced by the intense 
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
Flammagenitus is often grayish to brown in color because of the ash and 
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, gener ...
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 us ...
, 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 for ...
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 ...
s and forest fires can induce formation of this cloud, by mechanisms similar to those that form homogenitus
A homogenitus, anthropogenic or artificial cloud is a cloud induced by human activity. Although most clouds covering the sky have a purely natural origin, since the beginning of the Industrial Revolution, the use of fossil fuels and water vapor an ...
clouds. The presence of a low-level jet stream 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.
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 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 chose flammagenitus as the formal name of these clouds.
Appearance
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 entrainment (engineering), entrained or otherwise mixed into the mass. It is commo ...
associated with the fire. It also tends to expand because the ash involved in the cloud's formation increases the amount of condensation nuclei. 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 somet ...
, from which the lightning can start another fire.
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 ofcumulonimbus 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 cumulonimbus flammagenitus, 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