North Pacific Oscillation
North Pacific Oscillation
The North Pacific Oscillation (NPO) is a north–south seesaw in winter sea level pressure over the North Pacific on monthly (and shorter) time scales. It was defined in 1924 by Sir Gilbert Walker as “the opposition between Alaska, representing the area of low pressure, and Honolulu near the margin of the high pressure area, the coefficients in winter and spring being −0.70 and −0.52.”
The tropospheric circulation pattern linked with NPO variability is the west Pacific (WP) teleconnection. NPO/WP variability is linked to meridional displacements of the Asian-Pacific jet and Pacific storm tracks. Intercomparison of sea level pressure, geopotential height, and zonal wind anomaly structure reveals NPO to be a Pacific basin analog of the North Atlantic Oscillation.
NPO/WP variability is influential on North American winter hydroclimate: the positive NPO phase (deeper Aleutian low) results in warming of the North American continent, except for the western United States, and in less (more) precipitation over the Pacific Northwest (southern Great Plains). NPO/WP also impacts marginal sea ice zones, with the western Bering Sea and Sea of Okhotsk ice zones significantly extended during the positive NPO phase.
References:
Linkin, M. E., and S. Nigam, 2008: The North Pacific Oscillation–west Pacific teleconnection pattern: Mature-phase structure and winter impacts. J. Climate, 21, 1979–1997, [1]
Walker, G. T., 1924: Correlation in seasonal variations in weather IX: A further study of world weather. Mem. Indian Meteor. Dep., 24, 275–332.
Term Added 22 October 2014
