The Pacific Decadal Oscillation (PDO) is a pattern of Pacific climate variability that shifts phases on at least inter-decadal time scale, usually about 20 to 30 years. The PDO is detected as warm or cool surface waters in the Pacific Ocean, north of 20° N. During a "warm", or "positive", phase, the west Pacific becomes cool and part of the eastern ocean warms; during a "cool" or "negative" phase, the opposite pattern occurs.
The Pacific (inter-)decadal oscillation was named by Steven R. Hare, who noticed it while studying salmon production pattern results in 1997.
The prevailing hypothesis is that the PDO is caused by a "reddening" of the El Niño-Southern Oscillation (ENSO) combined with stochastic atmospheric forcing.
A PDO signal has been reconstructed to 1661 through tree-ring chronologies in the Baja California area.
The interdecadal Pacific oscillation (IPO or ID) display similar sea-surface temperature (SST) and sea-level pressure (SLP) patterns, with a cycle of 15–30 years, but affects both the north and south Pacific. In the tropical Pacific, maximum SST anomalies are found away from the equator. This is quite different from the quasi-decadal oscillation (QDO) with a period of 8-to-12 years and maximum SST anomalies straddling the equator, thus resembling the ENSO.
Read more about Pacific Decadal Oscillation: Mechanisms, Reconstructions and Regime Shifts, Predictability, Related Patterns
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—Henry David Thoreau (1817–1862)