The Pacific Decadal Oscillation

Byline: Nathan J. Mantua (1), Steven R. Hare (2) Keywords: Regime shift; climate impacts; PDO; IPO; NPO; fishery oceanography Abstract: The Pacific Decadal Oscillation (PDO) has been described by some as a long-lived El Nino-like pattern of Pacific climate variability, and by others as a blend of two sometimes independent modes having distinct spatial and temporal characteristics of North Pacific sea surface temperature (SST) variability. A growing body of evidence highlights a strong tendency for PDO impacts in the Southern Hemisphere, with important surface climate anomalies over the mid-latitude South Pacific Ocean, Australia and South America. Several independent studies find evidence for just two full PDO cycles in the past century: 'cool' PDO regimes prevailed from 1890--1924 and again from 1947--1976, while 'warm' PDO regimes dominated from 1925--1946 and from 1977 through (at least) the mid-1990's. Interdecadal changes in Pacific climate have widespread impacts on natural systems, including water resources in the Americas and many marine fisheries in the North Pacific. Tree-ring and Pacific coral based climate reconstructions suggest that PDO variations--at a range of varying time scales--can be traced back to at least 1600, although there are important differences between different proxy reconstructions. While 20th Century PDO fluctuations were most energetic in two general periodicities--one from 15-to-25 years, and the other from 50-to-70 years--the mechanisms causing PDO variability remain unclear. To date, there is little in the way of observational evidence to support a mid-latitude coupled air-sea interaction for PDO, though there are several well-understood mechanisms that promote multi-year persistence in North Pacific upper ocean temperature anomalies. Author Affiliation: (1) Joint Institute for the Study of the Atmosphere and Oceans, University of Washington, Seattle, WA, 98195-4235, U.S.A (2) International Pacific Halibut Commission, P.O. Box 95009, Seattle, WA, 98195-2009, U.S.A Article History: Registration Date: 12/10/2004