At the end of September, cold air at high altitudes above Antarctica had soared to more than 60 degrees above normal. It is a phenomenon known as "sudden stratospheric warming," and even though they take place far above Earth's surface, it has implications for weather at the surface.
SSW events occur within the layer of the atmosphere that extends from around 6-31 miles above Earth's surface. It is the same layer where we often find the stratospheric polar vortex, a counter-clockwise flow of cold air around a large area of low pressure that typically weakens during the summer and strengthens in the winter. The polar vortex gets our attention when it sends occasional lobes of bitterly cold air southward into the U.S.
Typically, the temperature high above Antarctica is around this time of the year would be close to 70 degrees below zero. This latest, what appears to be an SSW event, sent the temperature soaring to only 4 degrees below zero at the end of September.
"While these events are called 'sudden,' it's not sudden in the sense we would commonly use," explained Martin Jucker, Senior Lecturer in Atmospheric Science, Climate Change Research Centre, UNSW Sydney, per The Conversation. "The warming takes place over days or weeks. But they are sudden in the sense they're often unexpected, as they are difficult to predict."
These warm disruptions in the stratosphere start with large-scale atmospheric waves being pushed high into the atmosphere.
"Just like the ocean, the atmosphere has waves," added Jucker. "What's happening at present is that large-scale atmospheric waves have spread from the surface up into the stratosphere above Antarctica, bringing heat energy with them. As these waves interact with the strong winds of the vortex, they transfer this heat."
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There are impacts on the weather at the surface from these relatively far-flung warming events occurring in the stratosphere. It is an example of what meteorologists refer to as teleconnections, or "significant relationships or links between weather phenomena at widely separated locations on Earth, which typically entail climate patterns that span thousands of miles," according to NOAA.
After an SSW occurs during a winter in the U.S., within a couple of weeks, record cold can spread as far south as Florida. This latest SSW happened during the Antarctic winter. Jucker has been tracking SSW events and their effects on Australia's weather, where SSWs usually mean drier and warmer conditions for The Land Down Under.
"In 2019, sudden warming over Antarctica led to drier conditions in Australia," noted Jucker. "Research has shown this influenced the megafires over the Black Summer of 2019–2020. These events can create prime conditions for bushfires."
Australia's biodiversity suffered losses on an unprecedented scale, with over a billion animals estimated to have died or been displaced by catastrophic megafires that raged during the Black Summer. It was another example of an extreme weather event that was supercharged by our warming world.
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"The impact of climate change has led to longer, more intense fire seasons and an increase in the average number of elevated fire weather days," according to the Commonwealth Scientific and Industrial Research Organisation's summary of the wildfires.
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