03 Apr 2013:
Arctic Air Pressure System
Causes Unusual March Temperatures
A pronounced shift in Arctic air pressure systems has triggered unusually cold temperatures across North America, Europe, and northern Asia, while allowing a flood of warmer air into Greenland and
northeastern Canada, according to NASA. In recent weeks, the so-called Arctic Oscillation (AO) index — which tracks the relative pressure differential between the Arctic and mid-latitudes — dropped to the fifth-lowest reading ever recorded, NASA scientists said
. When the AO reaches this “negative” phase, scientists say, the pressure gradient between the Arctic and mid-latiutudes weakens, allowing Arctic air to stream south. This NASA graphic
depicts unusual land surface temperatures across the Northern Hemisphere, with Europe, Russia, and the U.S. experiencing temperatures as high as 5 to 15 degrees C below normal, while temperatures in Greenland were as high as 15 degrees C above normal. The United Kingdom recorded its fourth-coldest March since 1962, Germany experienced its coldest March since 1883, and Moscow had its coldest March since the 1950s.