Cloud PointField Guide

Special cloud — fire cloud (flammagenitus)

Pyrocumulus

The cloud a wildfire builds above itself

Written by Laurence WayneEntry No. 8Uncommon

Pyrocumulus: The cloud a wildfire builds above itself
Plate VIIIPhotograph by Frank Schulenburg, CC BY-SA 4.0.

Pyrocumulus — officially flammagenitus — is a cloud born from intense heat, towering above wildfires and erupting volcanoes. The fierce updraught of hot air lofts moisture and ash high into the sky, where the vapour condenses onto the ash particles to build a dirty, cauliflower-shaped cloud. If the air is unstable enough, it can grow into a full fire-driven thunderstorm complete with its own lightning.

Worth knowing

  • During Australia's 2019-20 'Black Summer', clusters of fire-storms lofted smoke from about 14 km up to roughly 35 km into the stratosphere — high enough to circle the globe and linger for months.
Note

Still unsure it's the same cloud? Our app, Cloud Point— on iOS and Android — reads a photo and returns the likely type with altitude, useful when a formation is fading faster than you can look it up.

Test yourselfThree levels

Choose a difficulty

What is a pyrocumulus cloud?

  1. aA cloud that grows out of the smoke plume above a fire or volcano
  2. bA cloud made of falling snow
  3. cA thin layer of night-glowing cloud
  4. dA coloured ring around the sun
Show answer

AnswerA cloud that grows out of the smoke plume above a fire or volcano

Pyrocumulus is a cumulus cloud that builds directly above the intense heat of a wildfire or volcanic eruption, rising out of the smoke.

How does a pyrocumulus cloud form?

  1. aCold air sinking over a glacier
  2. bIntense heat driving a strong updraught that lifts moisture and ash until the vapour condenses
  3. cSea spray freezing in cold air
  4. dSunlight refracting through ice crystals
Show answer

AnswerIntense heat driving a strong updraught that lifts moisture and ash until the vapour condenses

The fire's heat creates a powerful updraught that carries moisture and ash upward; as the air cools, water vapour condenses onto the ash particles to form the cloud.

Besides the fire's raw heat, what extra boost can drive a pyrocumulus to tower far higher than an ordinary thermal?

  1. aThe smoke blocking sunlight and cooling the column
  2. bLatent heat released as the rising moisture condenses, which adds buoyancy and accelerates the updraught
  3. cAsh making the air heavier so it sinks faster
  4. dThe fire stripping all moisture out of the air
Show answer

AnswerLatent heat released as the rising moisture condenses, which adds buoyancy and accelerates the updraught

Once the moist plume condenses, the latent heat of condensation warms the rising air further, adding buoyancy that can push the cloud up into a full pyrocumulonimbus.

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