Interdecadal Pacific Oscillation

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    Archived 19 October 2017

    The Interdecadal Pacific Oscillation (IPO) is a long-term oscillation of the Pacific Ocean. It lasts from 20 to 30 years, much longer than the El Niño Southern Oscillation. IPO can affect the strength and frequency of El Niño and La Niña. In New Zealand, the positive phase of IPO is linked to stronger west to southwest winds and more rain to the west. Such climate phases can affect our environment, industries, and recreational activities.

    We classified Interdecadal Pacific Oscillation as supporting information.

    Key findings

    • Three phases of the Interdecadal Pacific Oscillation occurred during the 20th century:
      • a positive phase, 1922–44
      • a negative phase, 1946–77
      • a positive phase, 1978–98 (Salinger et al, 2001).
    • IPO has been in a negative phase since 2000 (NIWA, 2011).

    Note: The annual average has been calculated by averaging the three-monthly average IPO index values for each year.

    Definition and methodology

    Interdecadal Pacific Oscillation (IPO) is a predictor of long-term climate phases. It is similar to a long-lived El Niño-like pattern of Pacific climate variability (Zhang et al, 1997). During positive phases, irregular warm sea-surface temperatures occur along the North Pacific coast of North America and irregular cool sea-surface temperatures in the interior North Pacific. Below-average surface-air pressures also occur over the North Pacific. This trend reverses in a negative phase.

    In New Zealand, the positive phase of IPO is linked to stronger west to southwest winds. The phase shift in 1977/8 led to more westerly winds in New Zealand. As a result, the west of the South Island was approximately 10 percent wetter and 5 percent cloudier than average, with more damaging floods than average. The north and east of the North Island were approximately 10 percent drier and 5 percent sunnier (NIWA, nd).

    IPO is similar, and nearly equivalent, to the Pacific Decadal Oscillation (PDO). PDO is a predictor of the impact of the climate oscillation in the northern Pacific.

    Data quality

    We classified Interdecadal Pacific Oscillation as supporting information.


     This supporting information is a partial measure of the ‘Variations in atmospheric circulation that drive New Zealand’s climate’ topic.


     The accuracy of the data source is of high quality.

    See Data quality information for more detail.


    NIWA (nd). Past climate variations over New Zealand. Accessed 5 June 2015 from

    NIWA (2011).Long-term fluctuations in river flow conditions linked to the Interdecadal Pacific Oscillation. Accessed 12 June 2015 from

    Salinger, MJ, Renwick JA, & Mullan, AB (2001). Interdecadal Pacific Oscillation and South Pacific climate. International Journal of Climatology, 21, 1705–1721. Available from

    Zhang, Y, Wallace, JM, & Battisti, DS (1997). ENSO-like interdecadal variability: 1900–93. Journal of Climate, 10, 1004–1020. Available from


    Published 21 October 2015

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