The Rise of pyroCbs

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Wildfires can become so intense that they produce thunderstorms.  This phenomenon of fire-triggered thunderstorms is called pyroCbs, which is short for pyrocumulonimbus clouds.

Pyrocumulonimbus clouds are also known as cumulonimbus flammagenitus.  Cumulonimbus flammagenitus stems from the Latin words meaning “flame” and “created from.” 

NASA refers to pyroCbs as the “fire-breathing dragon of clouds“.

While the exact physics behind these fire-triggered thunderstorms is still unclear, pyroCbs are triggered by the uplift of ash, smoke, and burning materials via super-heated updrafts.  Wildfire flames release enough heat and moisture into the atmosphere to produce thunderstorms. As these materials cool, clouds are formed that behave like traditional thunderstorms but without the accompanying precipitation.  

These pyroCbs produce dry lightening which can trigger further wildfires.

Illustration of thermal column created by a wildfire.  The wildfire [1] creates a heated uplift [2] bringing with it ash, smoke, and burning materials which then form into a pyroCbs. Source: Dake, Wikimedia Commons, CC BY 2.0
Illustration of thermal column created by a wildfire. The wildfire [1] creates a heated uplift [2] bringing with it ash, smoke, and burning materials which then form into a pyroCbs. Source: Dake, Wikimedia Commons, CC-BY 2.5

Scientists are studying how climate change, which is driving larger and more intense wildfires, are also creating a higher frequency of pyroCbs.

Fire-triggered thunderstorms are being generated in places that have never experienced this phenomenon before such as Texas, Portugal, South Africa, and Argentina (Related: Smoke from Australian Wildfires Reaches Atmospheric Highs).  pyroCbs are particularly destructive due to the tornado-strength vortexes that are produced.

A single pyroCb can send particles as high as 10 miles into the lower stratosphere according to  Dr. Glenn K. Yue, an atmospheric scientist at NASA Langley Research Center in Hampton, Virginia.

A pyrocumulonimbus cloud in eastern Washington, August 8, 2019. Photo: David Peterson (U.S. Naval Research Laboratory)
A pyrocumulonimbus cloud in eastern Washington, August 8, 2019. Taken from 30,000 feet (9 kilometers), the picture captures the smoke plume (gray) that fed the pyrocumulonimbus cloud (white). Photo: David Peterson (U.S. Naval Research Laboratory)

One of the Largest pyroCb Events Seen in the United States

On September 6, 2020, NASA’s Suomi NPP satellite was able to measure the “largest (if not the largest) pyroCb events seen in the United States,” according to Dr. Colin Seftor, Atmospheric Scientist at Goddard Space Flight Center in Greenbelt, Maryland.

On September 5, 2020, this natural-color image from NASA's Aqua satellite's Moderate Resolution Imaging Spectroradiometer (MODIS) instrument shows a pyrocumulonimbus cloud emerging from the Creek Fire. Image:  NASA Worldview.
On September 5, 2020, this natural-color image from NASA’s Aqua satellite’s Moderate Resolution Imaging Spectroradiometer (MODIS) instrument shows a pyrocumulonimbus cloud emerging from the Creek Fire. Image: NASA Worldview.

The pyroCb cloud was triggered by the  the Creek Fire which began in the Big Creek drainage area between Shaver Lake, Big Creek, and Huntington Lake in California. Sensors onboard the Suomi NPP satellite measured aerosol index values indicating this was one of the largest pyroCb events ever recorded.

Aerosol index image showing some of the highest values recorded from a pyrocumulonimbus cloud in the U.S. Credits: NOAA/NASA/C. Seftor
Aerosol index image showing some of the highest values recorded from a pyrocumulonimbus cloud in the U.S. Credits: NOAA/NASA/C. Seftor

References

Reed, J. (2020, October 16). California’s Creek fire blasts smoke into the stratosphere. NASA Applied Science. https://appliedsciences.nasa.gov/our-impact/news/californias-creek-fire-blasts-smoke-stratosphere

Struzik, E. (2019, January 24). Fire-induced storms: A new danger from the rise in wildfires. Yale E360. https://e360.yale.edu/features/fire-induced-storms-a-new-danger-from-the-rise-in-wildfires

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