Australia — Smoke from the 2009 Victoria bushfires travelled high into the stratosphere and circled the Earth for more than three months, a new study has found.
The finding challenges the notion that only volcanic particles are capable of passing into the upper layers of the atmosphere, and could have implications for climate modelling.
Jason Siddaway, a PhD researcher in atmospheric physics, and his supervisor Dr Svetlana Petelina of La Trobe University in Melbourne, publish their findings in the Journal of Geophysical Research.
Using satellite data collected by the Odin atmospheric satellite, the researchers tracked the movement of particles from the bushfires as they rose into the atmosphere.
“We started tracking it… and as it got higher and higher we got surprised,” Mr Siddaway said.
“It had so much kinetic energy that it penetrated past the tropopause and into the stratosphere.”
The researchers then noticed the particles travelled westward, circling the globe in about six weeks, reaching even higher altitudes. They remained in the stratosphere until the end of April, and by mid-June they had totally dispersed.
According to Mr Siddaway, the base of the stratosphere ranges in height from approximately 8 kilometres above the poles to 16 kilometres above the equator.
He says there have been reports of smoke reaching the lower parts of the stratosphere above Canada, but this is the first time it has been seen reaching this layer in the equatorial regions.
“Looking at the scientific literature we noticed there weren’t too many studies of bushfire smoke reaching this far up,” he said.
Mr Siddaway says the stratosphere is much calmer than the troposphere immediately below, which means particles remain there for a longer period of time.
This is important for climate models, which take into account the effects of particles in the atmosphere on incoming solar radiation.
The researchers says smoke particles from bushfires haven’t been taken into account, because it was thought they wouldn’t accumulate in such large quantities at this altitude.
Mr Siddaway admits it is difficult to know for certain what affect bushfire smoke would have in the stratosphere.
“If it was the normal type of aerosols that you could get from this type of forest bushfire, we think it could be a cooling effect.”
The findings could also change the way we view how particles move through the tropopause – the boundary between the troposphere and stratosphere.
“The tropopause is sort of known as a dynamic barrier,” Mr Siddaway said.
“So it’s interesting that the smoke plume was able to penetrate the tropopause. [This is] important in the context of atmospheric dynamic models.”