The most well-known mode of natural climate variability is the El Nino Southern Oscillation, an interannual climate oscillation originating in the tropical Pacific, but having effects around the world. The Atlantic lacks an interannual mode comparable to ENSO.  Instead, the dominant climate mode over the Atlantic is the NAO.  NAO is an oscillation involving the Azores High and Icelandic Low pressure centers and the westerly winds over the Atlantic.  It occurs in two states.  When the NAO is positive, the low and high pressure centers are intensified.  This leads to stronger westerlies that are shifted north.  This brings warm weather (stormy?) to northern Europe.  When the NAO is negative, the pressure cells diminish and the westerlies shift south.  Northern Europe is cold.

The atmospheric changes occur over the major deepwater formation regions in the Atlantic.  Deepwater production requires cold conditions which produce very dense water.  When the NAO is +, the Labrador Sea is cold which creates ideal conditions for deepwater formation.  When the NAO shifts, the deepwater formation in the LS diminishes, but increases in the Greenland Sea. The changes in water mass distribution and the winds lead to changes in the circulation of the Atlantic; however, the changes are typically delayed by a year or more.  In the western atlantic, the Gulf Stream shifts south during NAO- at the same time as the Labrador Current intensifies and extends.  In the east, there is evidence that a warm coastal jet extends during NAO+