Weakened 'polar vortex' blamed for N. American chill
PARIS (AFP) - The 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.