Weakened 'polar vortex' blamed for N. American chill

[ScienceRocks]

Weakened 'polar vortex' blamed for N. American chill

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.

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.

Weakened 'polar vortex' blamed for N. American chill

 

[Old Rocks]

The Rossby waves, those loops in the jet stream, are moving slower west to east, and looping further north to south, as explained by Dr. Jennifer Francis at the meeting of the American Meteorological Society.

[ame=http://www.youtube.com/watch?v=RtRvcXUIyZg]Weather and Climate Summit - Day 5, Jennifer Francis - YouTube[/ame]

Interesting this is the very kind of prediction that the deniers insist does not exist.