Context: The intense wildfires raging in the United States and Canada have spiked the occurrence of pyrocumulonimbus clouds. The development of these clouds has become more frequent in recent years.
About Pyrocumulonimbus clouds
- Pyrocumulonimbus clouds are thunder clouds created by intense heat from the Earth’s surface, either from large wildfires or volcanic eruptions. That is the reason why the prefix ‘pyro’ is used – meaning fire in Greek.
- For instance, these clouds were formed during the Australian bushfires of 2019-2020 when temperatures crossed 800 degrees Celsius.
Mechanism of formation of the clouds:
- The intense heat from the wildfire/ volcanic eruption warms the surrounding air which moves upward into the atmosphere.
- As this hot and very buoyant air (carrying water vapour, smoke, and ash) rises, it expands and cools down.
- Once it is cool enough, water vapour condenses on ash, forming a grey or brown cloud. At this stage, the cloud is known as a pyrocumulus cloud, also known as ‘fire cloud’.
- But if there is sufficient water vapour available and the upward movement of hot air intensifies, pyrocumulus clouds can evolve into a pyrocumulonimbus cloud.
Characteristics:
- These clouds can reach heights of 50,000 feet and generate their own systems of thunderstorms.
- Although pyrocumulonimbus clouds can produce lighting, they do not generate much rain. As a result, they can spark new wildfires many kilometres away from the main blaze.
- These clouds can also trigger strong winds that can make the spread of the wildfire faster and unpredictable.
Frequent occurrence of pyrocumulonimbus clouds:
- Before 2023, 102 pyrocumulonimbus were recorded globally in a single year on average — 50 of them were seen in Canada. However, during last year’s extreme wildfire season, 140 pyrocumulonimbus clouds were recorded in Canada alone.
- The exact reason for their frequent occurrence remains unclear. However, scientists believe that climate change and temperatures soaring across the world, leads to frequent wildfires, which may spike the occurrence of pyrocumulonimbus clouds.