At the end of August, climate scientists noticed a huge temperature anomaly in the stratosphere above Antarctica. According to scientists at Australia’s Bureau of Meteorology, the weeks that followed in September saw temperatures climb by as much as 35 degrees Celsius above normal value, shattering any previous records.
“Back in late August to early September, it was about 30 to 35 degree Kelvin warmer than normal in the upper to mid stratosphere over the Antarctic polar cap region, which was a record-breaking warming for that time of year,” said Eun-Pa Lim, a researcher at the Bureau of Meteorology. “Since then, the magnitude of the anomalous warming has reduced by about 15 degree Kelvin in the mid to lower stratosphere.”
The sudden warming is due to a weather phenomenon that happens regularly over the northern hemisphere, occurring every one or two years. In the southern hemisphere, however, such an event happens very rarely, its last instance being recorded in 2002.
The stratosphere is the second-highest layer of the planet’s atmosphere, extending in altitude from 13 km to 48 km (8 to 30 miles) high. The stratosphere contains over 15% of the total mass of the atmosphere. This is also where the ozone layer, which shields us from damaging UV radiation, is located.
Every winter in the southern hemisphere, high-velocity winds from the west form in the stratosphere due to temperature differences between the frigidly cold South Pole, which is in pitch darkness, and the relatively warmer ocean, which gets sunlight.
During spring, the polar region starts to warm, causing the stratospheric vortex to gradually weaken over a period of a couple of months. This year, this process happened much faster than before, causing the polar vortex to suddenly break down, reversing the direction of the associated westerly winds, which started blowing easterly. This is what technically happens during sudden stratospheric warming.
Lim says that this process is due to natural variations in the atmosphere, so it’s not necessarily connected to man-made climate change. In the future, Lim and colleagues plan on investigating the phenomenon in greater detail in order to learn as much as they can about the complex interplay between the stratosphere and troposphere. The latter is the lowest layer of the Earth, whose temperatures can actually cause melting in Antarctica.
The sudden stratospheric warming over Antarctica is expected to have consequences in Australia, which will experience hot, dry winds over the coming three months. According to the study published in Nature Geoscience, the weather phenomenon will causa Australia to experience less rainfall and higher temperatures during spring.
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