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The North Pacific Oscillation (NPO) is a teleconnection pattern first described by Walker and Bliss and characterized by a north-south seesaw in sea level pressure over the North Pacific.
Rogers, using surface atmospheric temperature from St. Paul, Alaska and Edmonton, identified two phases of the NPO, an Aleutian below (AB) phase that correspond to a deepened and eastward shifted Aleutian low and an Aleutian above (AA) phase that is the opposite.
During the positive (AB) phase sea level pressure is enhanced over a large region in the subtropics that extend poleward to 40N° and reduced at higher latitudes, westerlies are enhanced over the central Pacific and winter temperature are mild along much of the North America west coast but cooler than usual over Eastern Siberia and the United States South-West, precipitations are higher than usual over Alaska and the Great Plains.
The NPGO is the oceanic expression of the NPO.