Record low Arctic ice cover in January

NASA image created by Jesse Allen, using AMSR-E data and sea ice extent contours
courtesy of the National Snow and Ice Data Center (NSIDC). Caption by Michon Scott.

The National Snow and Ice Data Center has announced that Arctic sea ice cover for January 2011 was the lowest ever recorded by satellite records (which began in 1979). The ice extent averaged 13.55 million square kilometers (5.23 million square miles). It was 50,000 square kilometers (19,300 square miles) below the record low of 13.60 million square kilometers (5.25 million square miles), set in 2006, and 1.27 million square kilometers (490,000 square miles) below the 1979 to 2000 average. The image above shows the average Arctic sea ice concentration for January 2011, based on observations from the Advanced Microwave Scanning Radiometer for EOS aboard NASA’s Aqua satellite.

Ice extent in was particularly low in Hudson Bay, Hudson Strait and Davis Strait. These areas ordinarily freeze over by late November, but this year Hudson Bay did not completely freeze over until mid-January. The Labrador Sea still remains ice-free.

This depletion of winter sea ice occurred at the same time that the Northern Hemisphere was battered with heavy snow storms and unusual cold. These conditions are in fact related and have to do with the so-called Arctic oscillation. The Arctic oscillation is a pattern of large-scale movement of air which is characterized by opposite atmospheric pressure in the Arctic as compared with the Northern mid-latitudes (around 45°N). The oscillation determines the degree to which the Arctic air penetrates the mid-latitudes of the Northern Hemisphere. Positive Arctic oscillation means that the atmospheric pressure is low in the Arctic and high in the middle latitudes, which propels a strong and consistent jet stream over North America which keeps cold Arctic air away from the middle latitudes. When there is negative Arctic oscillation the high pressure is concentrated in the Arctic, meaning lower trade winds and more frequent invasion in the middle latitudes of cold Arctic winds. The pattern of atmospheric circulation is generally confined to the troposphere (the lower part of the Earth’s atmosphere) except in January through March where it involves the higher stratosphere and affects the westerly vortex that encircles the polar cap and keeps polar air locked up.

 

Positive mode of Arctic oscillation on left; Negative on right. (Figures by J. Wallace, University of Washington for National Snow and Ice Data Center.)

The Arctic oscillation was in negative mode in December and January, according to the U.S. National Oceanic and Atmospheric Administration, which forecast a return to positive mode in February 2011, but for how long is unknown. In fact, the negative mode broke down at the end of January, which generally results in ice formation.

The  air temperatures over the Arctic were 2-6º C above normal. The warm Arctic winter temperature was partly owing to the release of warm air in uncovered ocean sections. Frozen areas of the ocean reflect radiation, but darker unfrozen area not only absorb solar energy but release it back into the lower atmosphere.

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  1. February 17th, 2011

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