What are fire clouds or pyrocumulonimbus? How they formed over France's wildfires — Explained
As firefighters battle one of France's worst wildfire seasons in recent years, an unusual atmospheric phenomenon has drawn the attention of scientists: a pyrocumulonimbus (pyroCb)
As firefighters battle one of France's worst wildfire seasons in recent years, an unusual atmospheric phenomenon has drawn the attention of scientists: a pyrocumulonimbus (pyroCb), also known as a fire cloud or cumulonimbus flammagenitus. Firefighters Federation of France (FNSPF) said the giant wildfire in the country's southwest had generated a pyrocumulonimbus — a phenomenon they described as never before observed in France. The appearance of these towering clouds underscores not only the intensity of the fires but also the dangerous feedback loop they can create, worsening wildfire conditions. What is a pyrocumulonimbus or fire cloud? A pyrocumulonimbus is essentially a thunderstorm created by a wildfire rather than by the sun heating the Earth's surface. Quick answers to key questions • 5 QUESTIONS 1 What are pyrocumulonimbus clouds and how do they form? ⌵ Pyrocumulonimbus clouds, or fire clouds, form from intense wildfires that release heat, smoke, and moisture into the atmosphere. As this superheated air rises, it cools and condenses, potentially growing into a towering thunderstorm. 2 Why are pyrocumulonimbus clouds considered dangerous during wildfires? ⌵ These clouds create their own weather, producing strong winds and lightning that can spread fires unpredictably and ignite new wildfires, complicating firefighting efforts. 3 How do pyrocumulonimbus clouds affect wildfire conditions? ⌵ They can worsen wildfire behavior by generating powerful winds and severe weather, including hail and intense downdrafts, which pose additional risks to emergency responders and surrounding communities.
4 What role does climate change play in the formation of pyrocumulonimbus clouds? ⌵ While climate change does not directly create pyrocumulonimbus clouds, it increases the likelihood of conditions, like intense heatwaves and droughts, that facilitate their formation. 5 Have pyrocumulonimbus clouds been observed in recent wildfires? ⌵ Yes, although rare, pyrocumulonimbus clouds have been documented during significant wildfire events, including recent wildfires in France, underscoring the phenomenon's growing relevance as conditions worsen. According to NASA, these clouds form when an intense fire releases enormous amounts of heat, smoke and moisture into the atmosphere. The superheated air rises rapidly like a giant chimney, carrying ash and water vapour high into the sky. As the rising air cools, the moisture condenses into clouds. If the updraft is powerful enough, the cloud grows into a towering thunderstorm known as a pyrocumulonimbus. Scientists also refer to it as cumulonimbus flammagenitus, reflecting its fire-generated origin. How do fire clouds form? The process unfolds in several stages A massive wildfire heats the surrounding air to extreme temperatures. Hot air mixed with smoke and moisture rises rapidly. As it climbs higher, the air cools and water vapour condenses, forming a pyrocumulus cloud. If the plume continues rising into colder layers of the atmosphere, ice crystals develop inside the cloud. These ice particles generate electrical charges, transforming the cloud into a fully developed pyrocumulonimbus thunderstorm. Unlike ordinary thunderstorms powered by solar heating, the energy driving these clouds comes almost entirely from the wildfire itself.
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