Journal of Geophysical Research: Atmospheres

Cover image for Vol. 122 Issue 2

Impact Factor: 3.318

ISI Journal Citation Reports © Ranking: 2015: 27/184 (Geosciences Multidisciplinary)

Online ISSN: 2169-8996

Associated Title(s): Journal of Geophysical Research

Ash from huge Australian bushfires in 2009 circled the globe

On 7 February 2009, record high temperatures, low rainfall and humidity, and fast blowing winds caused sparks in the bush near the Australian city of Melbourne to ignite much of the southeastern region of the state of Victoria. In just a few days, more than 4500 km2 had burned and 173 people had died in what is considered the worst natural disaster in Australian history. The fires released so much smoke that daytime on 7 February was plunged into darkness. Indeed, soot particles and other aerosols are known to scatter and absorb solar radiation. However, airborne particles released by fires are typically thought to remain in the atmosphere close to their sources. In fact, climate models pay little attention to the scattering and absorbing effects of fire-borne aerosols because they are not believed to reach altitudes above 10 km, in the stratosphere, where circulation patterns would distribute a plume of pollution around the globe, possibly leading to global cooling effects. Ash from volcanic plumes has long been considered the sole method by which aerosols and gases could be injected into the stratosphere from the Earth's surface. However, Australia's bushfires of 2009 showed otherwise. Using data from the Optical Spectrograph and Infrared Imager System (OSIRIS) on board Sweden's Odin satellite, Siddaway and Petelina (2011) revealed that the dense bushfire smoke cloud from Australia's fires did in fact penetrate the stratosphere, on 11 February 2009. The smoke plume traveled westward in the stratosphere, circling the globe in about 6 weeks, steadily reaching higher and higher altitudes. However, as the fires waned, so too did the plume-the amount of particles in the stratosphere from the fire decreased by half every 19 days from mid-February to the end of April 2009. By mid-June 2009 the plume had dispersed. The authors note that the lifespan of these particles in the stratosphere was similar to what it would have been had they been released by a volcano, suggesting that extreme fires could have a global effect and should be considered in climate models. Further, recognizing such particles from other fires may help trace stratospheric circulation patterns, which are not yet completely defined.

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