An extremely rare atmospheric event has been cooking above Antarctica for the past couple of months and it could result in parts of the upper atmosphere creeping to upwards of 30°C (86°F). The phenomenon is called sudden stratospheric warming, the most dramatic meteorological phenomenon to take place in the stratosphere.
Scientists at the Australian Bureau of Meteorology (BOM) first noticed this event in the last week of August when stratospheric temperatures crept up higher than expected. Over the coming weeks, the warming continued to rise at a surprising rate. If their forecasts are on the money, we can be in store for the strongest sudden stratospheric warming event ever recorded.
Newly developed climate models have also highlighted how this could have a knock-on effect across parts of the Southern Hemisphere. Reporting their findings in the journal Nature Geoscience, a team from BOM and Monash University in Australia have shown that these conditions in Antarctica could even spark baking hot weather conditions in Australia.
The event is closely linked to the disturbance or breakdown of the polar vortex above Antarctica, the vast low-pressure zone that spirals around the South Pole in a clockwise direction (and counter-clocker in the North Pole).
Some warming can be expected around springtime in the upper reaches of the South Pole (a similar event occurs in the North Polar too). In any typical winter, temperature differences between the freezing polar region and the not-so-chilly Southern Ocean result in powerful winds in the stratosphere high above the South Pole as part of the polar vortex. As spring arrives and the Sun shifts further southward, warming temperatures cause these winds to gradually quieten down.
However, this change can sometimes occur too sharply. If so, bursts of air from the lower atmosphere push into the stratosphere, which weakens the polar vortex or can even reverses the flow of winds within it. The result is a steep rise in temperatures in the upper atmosphere, aka a sudden stratospheric warming event.
It’s unclear how often this event occurs. Scientists have only documented one other true sudden stratospheric warming event in the Southern Hemisphere, which occurred in September 2002, with records beginning in the 1950s. It's now looking like this year's event could be more intense than the 2002 event.
According to the new study, the event can have some far-reaching effects elsewhere in the world because it meddles with winds in the polar jet stream.
"Our study is significant because it is the first of its kind to identify and quantify a direct link between variations in the Antarctic polar vortex in spring and Australian hot and dry extremes from late spring to early summer," study author Dr Ghyslaine Boschat, an environmental research fellow at Monash University, said in a statement.
"This has major implications for the predictability of extreme climate in Australia, as well as possibly other regions of the Southern Hemisphere."