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The low Arctic pressure field is shown by purple colors in the figure for December 1968–1996. Strong Polar Vortex winds circle this pressure field, trapping cold air in the Arctic regions. In December 2009, this pattern broke down, Polar Vortex winds weakened (green colors) and cold Arctic air (which parallels the color contours) flowed southward.
Download here. (Credit: NOAA)
It’s a puzzle: How could warmth in the Arctic produce frigid conditions elsewhere?
NOAA scientists may have a clue.
Extremely cold winds have swept down through the Northern Hemisphere recently, reaching as far south as the state of Florida and causing record low temperatures in January. The unusually cold winter of 2009–2010 – which saw massive snowstorms dubbed “Snowpocalypse” and “Snowmageddon” — and the frigid start to 2011 in the eastern United States and Europe have scientists talking about what might be influencing the weather.
Dr. James Overland, a scientist at NOAA’s Pacific Marine Environmental Laboratory (PMEL) in Seattle, has been studying the changing conditions in the Arctic for 30 years. He explains why the deterioration of the Polar Vortex could be leading to some of these extreme winter weather events.
“When the Polar Vortex — a ring of winds circling the Arctic — breaks down, this allows cold air to spill south, affecting the eastern United States and other regions,” says Dr. Overland. “This can result in a warmer-than-average Arctic region and colder temperatures that may include severe winter weather events on the North American and European continents.”
A Polar Vortex link to Winter 2009-2010?
The Polar Vortex is a strong wind flowing around a low-pressure system normally present over the Arctic in winter. Average December values from 1968–1996 show the Polar Vortex remaining strong and helping to keep the cold air in the Arctic region. During winter of 2009–2010, this normal pattern broke down, and a weakened Polar Vortex allowed cold Arctic air to move southward.
“In December 2009, the Arctic was 9 degrees F warmer than normal, and mid-latitude continents were 9 degrees F cooler than normal, with record cold and snow conditions in northern Europe, eastern Asia and eastern North America,” says Dr. Overland. “This is the Warm Arctic-Cold Continents pattern. The winter of 2009–2010 had especially extreme weather in the U.S. as moisture from El Nino hit cold air from the Arctic.”
A map of the Warm Arctic-Cold Continents pattern for December 2010 shows warmer than usual air temperature (red) in the Arctic, especially for regions that were sea-ice-free in summer — north of Alaska, Hudson Bay and in the Barents Sea. Cold continents (purple) are seen where Arctic air has penetrated southward.
Download here. (Credit: NOAA)
Why are we seeing these changes now?
According to the 2010 Arctic Report Card, there is reduced sea summer sea ice cover, record snow cover decreases, and record temperatures. Could these changes be linked to the weakened Polar Vortex and extreme winter weather events?
Many factors, including natural climate variability, can produce extreme weather events. But, there also is a potential impact from Arctic regions, where solar heat absorbed by recently ice-free regions of the ocean warms the atmosphere during autumn, impacting the winds. More research is needed to study the causes and extent of the recently observed Warm Arctic-Cold Continent pattern.
“Some scientists are beginning to suspect that the lack of sea ice allows the oceans to pump heat into the atmosphere in the Arctic in a way that could impact weather patterns such as the North Atlantic Oscillation,” said Mark Serreze, director of the National Snow and Ice Data Center. “The idea is still very much in its infancy, but it’s worth looking into. If it turns out to be right, it could help to explain the frigid winters the eastern United States and Europe have experienced these past two years.”
The North Atlantic Oscillation (NAO) is a natural climate pattern that is the dominant mode of winter climate variability for the region, which ranges from central North America to Europe and into Northern Asia. A strongly negative NAO can indicate a breakdown of the Polar Vortex. Last winter, there were two extreme cold continent events — and the breakdown of the Vortex, as measured by the NAO, was the most extreme on record for the past 145 years.
Undoubtedly, changes in the Arctic are being felt near and far. The winters of 2009 and 2010 serve as a jumping off point for more research to determine potential linkages between Arctic changes and continental weather to help predict if the Northern latitudes will witness colder winters in the future as more summer sea ice is lost.
Learn more about NOAA’s “cool” work in the Arctic: Visit www.arctic.noaa.gov.
Posted Feb. 28, 2011