Abnormally hot days may hit Australia's south-east after rare sudden warming over Antarctica

"The phenomenon called sudden stratospheric warming is extremely unusual in the southern hemisphere. It only previously occurred in 2002 and 2019, the latter contributing to a worsening of the black summer bushfires. In early September this year, air temperatures 30km above the Southern Ocean and Antarctica began to climb, and are now sitting about 30C warmer than average, according to Dr Martin Jucker, a senior lecturer in atmospheric science at the University of New South Wales."

"Normally it's about minus 50C, so now it's minus 20C it's still pretty cold, Jucker said. The warming is accompanied by a slowdown in the powerful winds above the Earth's polar regions, called the polar vortex. Usually those winds are about 200km/h but are now about 100km/h. Those changes are likely to drive warmer and drier weather patterns at the surface, particularly in NSW and Victoria. But the effects this time around are partly unknown, given the Bureau of Meteorology's forecast for wetter conditions."

"So there is a balancing act between these very warm ocean temperatures, which would drive wet weather for us, versus the stratosphere, which would drive dry weather, Jucker said. Who wins? I don't know. According to the bureau, weather changes associated with past stratospheric warming events have had their strongest effects in New South Wales and southern Queensland, with increased springtime temperatures and less rainfall."

A rare rise in stratospheric temperatures over Antarctica may influence weather into summer. Sudden stratospheric warming events are extremely unusual in the southern hemisphere and previously occurred only in 2002 and 2019, with 2019 worsening black summer bushfires. In early September air temperatures about 30km above the Southern Ocean and Antarctica climbed to roughly 30C warmer than average, from about −50C to −20C. The warming has slowed the polar vortex, reducing upper-level winds from around 200km/h to about 100km/h. These changes are likely to promote warmer, drier surface conditions in New South Wales and Victoria, but very warm ocean temperatures and a Bureau forecast for wetter conditions create uncertainty.

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