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Arctic Shift Brought This Winter's Chill January 15, 2010
Arctic Oscillation
Since the 1970s, the Arctic Oscillation has tended to stay in the phase that kept much of North America and Europe warmer than normal in winter ... until now.
A rare disruption of the Northern Hemisphere circulation since mid-December dislodged almost all of the frigid air around the Arctic, sending it thousands of miles to the south.

The surge chilled parts of Asia, Europe and North America with some of the most severe winter conditions in decades.

The Arctic Oscillation also caused temperatures at high latitudes around the North Pole to shoot up to levels much warmer than normal, equalizing the atmospheric heat balance.

The U.S. Center for Atmospheric Research points out that such hemispheric chills have become infrequent since 1990. And it says this winter’s cold is in bitter contrast to the above-normal weather in Europe and North America during November.

But in a possible sign that the overall global warming is not over despite the temporary northern chill, Australia’s second-largest city suffered through its hottest overnight summer weather on record.

Melbourne’s air temperature remained above 90 degrees Fahrenheit all night on the morning of Jan. 12.

Graphic: J. Wallace - University of Washington