Pacific Decadal Oscillation [PDO]

The Role of the Pacific Decadal Oscillation (PDO)

The Pacific Decadal Oscillation (PDO) is often described as a long-lived El Niño-like pattern of Pacific climate variability. As seen with the better-known El Niño/Southern Oscillation (ENSO), extremes in the PDO pattern are marked by widespread variations in the Pacific Basin and the North American climate.

In parallel with the ENSO phenomenon, the extreme phases of the PDO have been classified as being either warm or cool, as defined by ocean temperature anomalies in the northeast and tropical Pacific Ocean.

When SSTs are anomalously cool in the interior North Pacific and warm along the Pacific Coast, and when sea level pressures are below average over the North Pacific, the PDO has a positive value. When the climate anomaly patterns are reversed, with warm SST anomalies in the interior and cool SST anomalies along the North American coast, or above average sea level pressures over the North Pacific, the PDO has a negative value.

The NCEI PDO index is based on NOAA's extended reconstruction of SSTs (ERSST). The supreme importance of the PDO for long-range meteorology lies in its role as a modulator: a positive PDO amplifies the impacts of a concomitant El Niño event, while a negative PDO exacerbates the effects of La Niña, cascading weather patterns globally, including in Europe.