More than four months after it formed, a large blob of sooty dust from Australia’s massive bushfires is still circling the southern hemisphere.
NIWA atmospheric scientist Richard Querel says that, unusually, the dust reached high into the stratosphere, where it is still detectable.
Measurements from a space-based LIDAR instrument for the month of January 2020 show dust from the Australian bushfires in the stratosphere spread across the southern hemisphere, while the northern hemisphere shows dust lingering from volcanic eruptions more than six months earlier. Photo: Jean-Paul Vernier / NASA
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Hundreds of large bushfires raged across the Australian states of New South Wales, Victoria and ACT in December 2019 and January 2020, in a fire season dubbed the Black Summer.
Large smoke plumes travelled across the Tasman to New Zealand, where people could smell the smoke as a dusty haze obscured the sky.
Remarkably, more than four months later, the remains of that smoke is still circling the globe.
Imagery from the Japanese weather satellite Himawari-8, taken on 1 January 2020, shows a blanket of smoke covering the entire South Island. Photo: CC BY 4.0
Richard works at the world-renowned Lauder Atmospheric Research Station, in Central Otago.
“The whole atmosphere is being measured by a variety of our instruments,” says Richard, and some of those instruments, such as lasers and balloons, have been used to monitor the bushfire smoke from the ground. These data complement other data collected from space by various satellites.
“We saw one particular blob come over about 50 days after it left Australia,” says Richard. “It went across the Pacific [to South America] and then came back. And by the time it was over us it was between 25 and 30 kilometres high, whereas originally the fire would have put it to maybe 15 kilometres.”
Richard says the dark dust was elevated an extra 10 kilometres by the sun.
“The sun was heating all the carbon aerosol, the soot, that was in this cloud and that’s a very unique feature … All that solar thermal heating slowly heated up the air parcel itself and that slowly rose.”
Richard says it just so happened that the material in the smoke cloud was small, light particles which made it buoyant.
“Since the fires were so energetic, it pushed the smoke up and it pierced into the lower stratosphere [where it] dehydrated” says Richard.
Photo: NASA
Round the world in a dust cloud
The blob has now been around the globe several times and the dust has since ascended to twice the original height. “Some of that material is up at 32 to 35 kilometres now.”
It is one of the largest plumes of smoke observed by satellites that high in the stratosphere. At its maximum, Richard says the smoke was spread across mid latitudes in the southern hemisphere. “There was pieces and pockets of it everywhere.”
One large pocket that passed directly over Lauder early on was about five kilometres high and hundreds of kilometres wide.
Photo: AFP
More CO, less ozone
NIWA atmospheric scientist Dr Richard Querel. Photo: NIWA
The high-altitude dust has been associated with elevated levels of carbon monoxide, water vapour and nitrous oxide, which is unusual at that altitude.
“It’s both a transport issue, that you brought this low altitude air upward, and there are also some chemical processes happening inside that smoke cloud,” says Richard.
When Richard and the Lauder team were measuring the large blob that passed directly overhead they recorded ozone levels that were much lower than normal. Richard says this was a temporary feature that was not of concern.
In late April, Richard says the smoke is now an indistinct blur across the southern hemisphere that is “spread everywhere … it’s sort of a smear if you look at satellite measurements nowadays.”
He suggests that we might see this unusual situation more often in future as climate change means more intense fire seasons with very energetic fires.
