Pyrocumulonimbus

Article By:

Fromm, Michael U.S. Naval Research Laboratory, Washington, DC.

Stocks, Brian Wildfire Investigations Ltd., Ontario, Canada.

Last reviewed:2010

DOI:https://doi.org/10.1036/1097-8542.YB100226

In the northern hemisphere summer of 1998, smoke from forest fires was detected in the stratosphere, up to 7 km above the troposphere. Initially, the observations of these particles were shrouded in mystery, as there had been no known volcanic eruption. However, these “mystery layers” were abundantly evident in measurements taken by at least three satellite-based and multiple ground-based instruments. Because aerosol layers in the stratosphere have a long residence time and, in the case of volcanic particles, are known to have an impact on climate, there was a compelling need to find their source. Subsequent investigation, using winds to find a common location, pointed to the boreal forest of northwestern Canada, where many large wildfires were active then. Later, a specific and unique form of explosive thunderstorm—pyrocumulonimbus—was discovered to be the “smoking gun,” and thus the identification of the stratospheric particles as smoke was confirmed. This discovery is a fundamental challenge to the accepted views of thunderstorm energetics within the atmospheric science community.

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