Smoke from Australian Wildfires Reaches Atmospheric Highs

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The wildfires that swept across Australia during the last bushfire season were some of the most extreme and dangerous ever recorded. Drought combined with increasing above-average heat days helped perpetuate the wildfires, which burned across hundreds of thousands of acres and caused the mass evacuation of urban and rural areas.

The smoke from the wildfires not only impacted Australian population centers but drifted far into the atmosphere as well. In particular, researchers were interested in the wildfires that raged between December 29th, 2019, and January 4th, 2020. This period released approximately 300,000-900,000 metric tons of smoke into the atmosphere.

Pyrocumulonimbus Clouds

As wildfires produce smoke, this material combines in the atmosphere to create what is known as a pyrocumulonimbus cloud, or pyroCb for short. A pyroCb is essentially a fire-created thunderstorm that rises high into Earth’s atmosphere. In this particular period, researchers observed the pyroCb plume higher in the stratosphere than ever previously recorded- 31 kilometers up.

Taken at about 30,000 feet (9 kilometers) over eastern Washington, the  smoke plume (gray) feeds the pyrocumulonimbus cloud (white).  Photo: David Peterson (U.S. Naval Research Laboratory), public domain, August 8, 2019.
Taken at about 30,000 feet (9 kilometers) over eastern Washington, the smoke plume (gray) feeds the pyrocumulonimbus cloud (white). Photo: David Peterson (U.S. Naval Research Laboratory), public domain, August 8, 2019.

The atmospheric smoke from these fires lingers in the stratosphere months later. The stratosphere and the ozone layer in it provide essential protection for Earth from the sun’s harmful ultraviolet radiation. Researchers are still collecting data on this plume, which was observed to be spinning with the force of rotational atmospheric winds that allowed the heat-propelled smoke to move high into the ozone layer. These winds had not been previously seen affected wildfire smoke, which prompted much interest. 

Plume tracking map (top)  and (bottom) showing altitude by time.  Source: Kablick et al., 2.0.
Plume tracking map (top) and (bottom) showing altitude by time. Source: Kablick et al., 2020.

Ozone Layer Impacts

Researchers are particularly interested in whether or not the smoke has a permanent chemical effect on the ozone layer; chemical reactions can break down ozone, and pyroCb clouds can displace ozone-rich gasses in the stratosphere. Whether or not this wildfire event will leave a permanent scar on the stratosphere has yet to be seen, as the smoke is still present over an area roughly the size of the width of the state of Montana. Researchers continue to use on the ground data as well as satellites and weather balloons to collect data on wildfires. 

Current and Future Implications

Similar studies were conducted in 2017 during an extreme fire season that hit areas of the Pacific Northwest in the United States. In this case, the smoke plume rose 23 kilometers into Earth’s atmosphere. Both the Pacific Northwest study data and now Australia’s wildfire data provides researchers with baseline information on the impacts that large amounts of smoke in the upper atmosphere can have. Some use this data to model potential nuclear war scenarios, which would pump massive amounts of smoke and other chemicals into Earth’s upper atmosphere. 

References

Kablick III, G. P., Allen, D. R., Fromm, M. D., & Nedoluha, G. E. (2020). Australian pyroCb smoke generates synoptic‐scale stratospheric anticyclones. Geophysical Research Letters47(13), e2020GL088101. https://doi.org/10.1029/2020GL088101

Temming, M. (2020, June 13). Smoke from Australian fires rose higher into the ozone layer than ever before. Science News. https://www.sciencenews.org/article/smoke-australian-fires-rose-higher-ozone-layer-than-ever-before

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