Highlights
Arctic sea ice extent for January 2011 was the lowest in the satellite record for that month.
The Arctic oscillation persisted in its strong negative phase for most of the month…[and]…cold conditions in northern Europe and the U.S. are linked to the strong negative mode of the Arctic oscillation.
Cold air is denser than warmer air, so it sits closer to the surface. Around the North Pole, this dense cold air causes a circular wind pattern called the polar vortex , which helps keep cold air trapped near the poles. When sea ice has not formed during autumn and winter, heat from the ocean escapes and warms the atmosphere. This may weaken the polar vortex and allow air to spill out of the Arctic and into mid-latitude regions in some years, bringing potentially cold winter weather to lower latitudes.
Dr. James Overland of NOAA Pacific Marine Environmental Laboratory (PMEL) recently noted a link between low sea ice and a weak polar vortex in 2005, 2008, and the past two winters, all years with very low September sea ice extent. Earlier work by Jennifer Francis of Rutgers University and colleagues also suggested a relationship between autumn sea ice levels and mid-latitude winter conditions.
[In January] average Arctic sea ice stood at 1.27 million square kilometers (490,000 square miles) below the 1979 to 2000 average.
Air temperatures over much of the Arctic were 2 to 6 degrees Celsius (4 to 11 degrees Fahrenheit) above normal in January. Over the eastern Canadian Arctic Archipelago, Baffin Bay/Davis Strait and Labrador Sea, temperatures were at least 6 degrees Celsius (11 degrees Fahrenheit) higher than average. Temperatures were near average over the western Canadian Arctic Archipelago and Scandinavia.
As in December 2010, the warm temperatures in January came from two sources: unfrozen areas of the ocean continued to release heat to the atmosphere, and the wind patterns accompanying the negative phase of the Arctic oscillation brought warm air into the Arctic.
While the Arctic has been warm, cold and stormy weather has affected much of the Northeast U.S. and Europe. Last winter also paired an anomalously warm Arctic with cold and snowy weather for the eastern U.S. and northern Europe.
These images show high and low atmospheric pressure patterns for January 2011 (left) and the January 1968-1996 average (right). Yellows and reds show higher pressures; blues and purples indicate lower pressures, as indicated by the height of the 850 millibar pressure level above the surface, called the pressure surface. Normally, the pressure surface is nearer to the surface around the pole, winds follow the pressure contours around the pole (the polar vortex), and cold air is trapped in the Arctic. This year, the pressure surface is allowing cold air to spill out of the Arctic into the mid-latitudes.
The source article Arctic Sea Ice News & Analysis was published February 2, 2011 by NOAA National Snow and Ice Data Center .
