Wildfires in the United States and Canada have recently become so severe that they are generating a rare type of cloud known as pyrocumulonimbus. These clouds have the potential to produce thunder and trigger additional fires.
Frequency of Pyrocumulonimbus Clouds
- Historical Data: Prior to 2023, an average of 102 pyrocumulonimbus clouds were recorded globally each year, with 50 occurring in Canada, according to a report in Nature.
- Recent Trends: In the extreme wildfire season of the previous year, 140 pyrocumulonimbus clouds were recorded in Canada alone.
Conditions for Formation
Not all wildfires lead to the creation of pyrocumulonimbus clouds. These clouds form under specific conditions:
- Heat Source: Pyrocumulonimbus clouds typically form from extremely hot wildfires or volcanic eruptions. For example, the Australian bushfires of 2019-2020 created these clouds when temperatures exceeded 800 degrees Celsius.
- Process:
- Intense heat from the fire warms surrounding air, which then rises into the atmosphere.
- As the hot air expands and cools, water vapour condenses on ash, forming a pyrocumulus cloud (also known as a ‘fire cloud’).
- If sufficient water vapour is present and upward air movement intensifies, the pyrocumulus cloud can evolve into a pyrocumulonimbus cloud.
Characteristics and Impact
- Height and Storms: Pyrocumulonimbus clouds can reach up to 50,000 feet and generate their own thunderstorm systems.
- Lightning and Rain: While they can produce lightning, they do not generate significant rainfall. Consequently, they can ignite new wildfires far from the main blaze and cause strong, unpredictable winds that accelerate the spread of fires.
Scientific Understanding
- Research Status: The study of pyrocumulonimbus clouds is relatively new compared to other extreme weather events.
- Role of Climate Change: Scientists suggest that climate change may be contributing to the increased frequency of these clouds. Higher global temperatures are leading to more frequent and intense wildfires, which in turn may result in more pyrocumulonimbus clouds.
Expert Opinion
David Peterson, a meteorologist at the US Naval Research Laboratory, notes: “In a general sense, if you have more fires you’ll have more pyrocumulonimbus clouds because there are more opportunities for them to form, but atmospheric conditions also play a role. Intense wildfires definitely increase the odds.”
Multiple-Choice Questions (MCQs):
- What type of clouds are generated by intense wildfires and volcanic eruptions?
- A) Stratus clouds
- B) Cumulus clouds
- C) Pyrocumulonimbus clouds
- D) Altostratus clouds
- Before 2023, how many pyrocumulonimbus clouds were recorded globally on average per year?
- A) 50
- B) 75
- C) 102
- D) 140
- What is the minimum temperature at which pyrocumulonimbus clouds were observed during the Australian bushfires of 2019-2020?
- A) 400 degrees Celsius
- B) 600 degrees Celsius
- C) 800 degrees Celsius
- D) 1000 degrees Celsius
- What is a significant characteristic of pyrocumulonimbus clouds compared to other clouds?
- A) They produce heavy rainfall.
- B) They generate strong winds and can spark new wildfires.
- C) They are typically low-altitude clouds.
- D) They are harmless and do not affect weather conditions.
- According to David Peterson, what factor increases the likelihood of pyrocumulonimbus clouds forming?
- A) Lower temperatures
- B) Higher humidity
- C) More intense wildfires
- D) Less atmospheric moisture