A rare atmospheric phenomenon has caused the air above Antarctica to become much warmer than usual, with scientists recording record temperatures in the stratosphere.
Eun-Pa Lim of Australia's Bureau of Meteorology and colleagues noted that the air above Antarctica was getting warmer in late August. In the weeks that followed, this warming intensified, seeing temperatures reach as much as 35 degrees Kelvin above normal.
Warming was the result of sudden stratospheric warming - a phenomenon that occurs regularly in the Northern Hemisphere approximately once every year or two, Lim told Newsweek. In the Southern Hemisphere, however, it is much rarer and has been observed only once before in 2002.
"In late August to early September, it was about 30 to 35 degrees Kelvin warmer than normal in the upper and middle stratosphere in the Antarctic ice cap region, which was a record warming for this time of year," said Lim. "Since then, the magnitude of anomalous warming has reduced by about 15 degrees Kelvin in the medium to low stratosphere."
Every winter, swift winds from the west develop in the stratosphere - the second layer in the earth's atmosphere above the troposphere. This layer extends about 50 kilometers high, with the ozone layer inside it. These winds, which can reach 240 kilometers per hour, develop due to temperature differences between the South Pole, where there is no sunlight, and the ocean, which still receives sunlight.
“As the sun shifts south during spring, the polar region begins to heat up. This warming causes the stratospheric vortex and associated western winds to gradually weaken over a few months, ”said Lim. Some years, this happens faster than normal, with lower atmosphere air warming the stratosphere, causing the weakening of winds. “Rarely, if the waves are strong enough, they can break the polar vortex quickly, reversing the direction of the winds and becoming farther east. This is the technical definition of 'sudden stratospheric warming'. ”
Sudden stratospheric warming is the result of natural variations in the atmosphere, she said, adding that it appears that this event is the result of random variability. Lim added that she and the team now plan to analyze what happened to the warming in order to better understand the physical mechanisms of the relationship between the stratosphere and the troposphere.
"The current event started with very fast and strong warming, but warming has been maintained in the stratosphere and has not yet affected the lower atmosphere, which is very unusual," she said.
Sudden stratospheric warming is expected to bring hot, dry winds over Australia over the next three months, the researchers say. In a study published in Nature Geoscience, the team put rising temperatures in a model that provides predictions for the Southern Hemisphere. The findings showed that Australia is likely to have less rain and warmer spring temperatures, potentially increasing the risk of forest fires.
"This has major implications for the predictability of extreme weather in Australia as well as possibly in other regions of the southern hemisphere," study co-author Ghyslaine Boschat of Australia's Monash University said in a statement.