The North Pacific Oscillation (NPO) is a
teleconnection pattern first described by
Walker and Bliss
[1] and characterized by a north–south seesaw in
sea-level pressure over the North Pacific Ocean.
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.
[2]
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 effects of the NPO propagate into the subtropics and
tropics through another climate mode, the
Pacific Meridional Mode.
[3]
The
North Pacific Gyre Oscillation (NPGO) is the oceanic expression of the NPO.
[4]