The left-hand image depicts the pattern seen in winters from 1986 to 1991: The Arctic climate was determined by a "tripolar" pattern dependent on the Icelandic Low, the Azores High and a subtropical high in the Pacific. The right-hand image shows the latest development. The pattern is now "dipolar" with cool air being shoved aside as the Icelandic Low and Azores high move in a north-easterly direction. The result is masses of warm air moving into the Arctic region.