For those of you interested in the Arctic-like conditions making the collective fingers and toes of Western Europe blue, there is an interesting blog post on the Wunder Blog. Some frozen individuals in London and New York decry global warming when they have to turn up their thermostats in early December, but the fact is that while Western Europe and the Eastern U.S. are cooling down, the Arctic is warming up. This is part of the “Hot Arctic – Cold Continents” pattern. All of the cool air that should be trapped in the Arctic, helping to keep sea ice frozen, is spilling southward. Meanwhile, more warm air goes north to replace the cold air flowing out, resulting in temperatures in Greenland that are 10+ above normal, while Heathrow is socked in by snow. Such reversals of meteorological function are caused by alterations in the North Atlantic Oscillation. When there is a small difference in air pressure between the “Icelandic Low” and “Azores High,” the north and south poles of the oscillation, respectively, the Arctic will warm, while the continents will freeze.
This illustration from a March 2009 article in Nature by Nicolas Gruber (“Carbon cycle: Fickle trends in the ocean,”) demonstrates that when the Icelandic Low and Azores High are both high in pressure (meaning that the difference between the two would be minimal), winter storms will blow across Northern Europe.