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- Mar 16, 2010
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Weakened 'polar vortex' blamed for N. American chill
Weakened 'polar vortex' blamed for N. American chillThe bitter chill gripping North America is a result of Arctic air that has spilled southwards, and global warming may be a cause, an expert said on Monday.
Arctic air is normally penned in at the roof of the world by a powerful circular wind called the polar vortex, said Dim Coumou, a senior scientist at the Potsdam Institute for Climate Impact Research (PIK) near Berlin.
When the vortex weakens, the air starts heading southwards, bringing exceptional snow and chill to middle latitudes.
The weather shift is also helped by changes in a high altitude wind called the jet stream.
This convection, which usually encircles the northern hemisphere in a robust and predictable fashion, starts to zigzag, creating loops of extremely cold weather or unseasonably mild weather, depending on the location.
"We've seen a strong meandering of the jetstream, and the cold air associated with the polar vortex has been moving southwards, and in this case over the eastern parts of Canada and the United States, bringing this extreme cold weather," said Coumou.
The phenomenon has occurred repeatedly in recent winters, he noted.