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A flammagenitus cloud, also known as a flammagenitus, pyrocumulus cloud, or fire cloud, is a dense cumuliform cloud associated with fire or volcanic eruptions. A flammagenitus is similar dynamically in some ways to a
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 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 energy in transfer between a thermodynamic system and its surroundings by such mechanisms as thermal conduction, electromagnetic radiation, and friction, which are microscopic in nature, involving sub-atomic, ato ...
ing of the air
An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...
from the surface. The intense heat induces convection
Convection is single or Multiphase flow, multiphase fluid flow that occurs Spontaneous process, spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoy ...
, 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. Moisture is defined as water in the adsorbed or absorbed phase. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some comme ...
. Phenomena such as volcanic eruption
A volcanic eruption occurs when material is expelled from a volcanic vent or fissure. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior h ...
s and forest fires A forest fire
A wildfire, forest fire, or a bushfire is an unplanned and uncontrolled fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identified as a bushfire ( in Au ...
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 thermal wind, air currents in the Earth's Atmosphere of Earth, atmosphere.
The main jet streams are located near the altitude of the tropopause and are westerly winds, flowing west to east around the gl ...
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 (whic ...
(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 natural phenomenon consisting of electrostatic discharges occurring through the atmosphere between two electrically charged regions. One or both regions are within the atmosphere, with the second region sometimes occurring on ...
. 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 () 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. Above the lower portions of the cumulonimbus the water va ...
, a thundercloud, and is called cumulonimbus flammagenitus. The World Meteorological Organization formerly classified flammagenitus and cumulonimbus flammagenitus respectively as cumulus (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
Flammagenitus is often grayish to brown in color because of the ash and smoke
Smoke is an aerosol (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 unwante ...
associated with the fire. It also tends to expand because the ash involved in the cloud's formation increases the amount of condensation nuclei.
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 () 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. Above the lower portions of the cumulonimbus the water ...
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 Volcanism