Interdecadal Pacific Oscillation

  • Image, interdecadal pacific oscillation.

    The Interdecadal Pacific Oscillation (IPO) is a long-term oscillation of sea-surface temperatures in the Pacific Ocean that can last from 20 to 30 years. Its positive and negative phases affect the strength and frequency of El Niño and La Niña. In New Zealand, the positive phase is linked to stronger west to southwest winds and more rain in the west. This trend is reversed during the negative phase.

    The IPO is one of three climate oscillations that affect our weather. These changes in air pressure, sea temperature, and wind direction can last for weeks to decades, depending on the oscillation.

    We classified Interdecadal Pacific Oscillation as supporting information.

    Key findings

    The Interdecadal Pacific Oscillation (IPO) was in a positive phase during 2014–16 and a negative phase during 1999–2013.

    • Three phases of IPO occurred during the 20th century:
      • a positive phase, 1913–44
      • a negative phase, 1945–76
      • a positive phase, 1977–98
    Note: The annual average is calculated by averaging the three-monthly average IPO index values for each year (Met Office, Hadley Centre for Climate Change, 2016). Positive phases are represented by positive index numbers; negative numbers represent negative phases.

    Definition and methodology

    Three climate oscillations affect New Zealand:

    • Interdecadal Pacific Oscillation (IPO) lasts 20–30 years
    • El Niño-Southern Oscillation (ENSO) occurs every 2–7 years and lasts around a year
    • Southern Annular Mode can last for several weeks, but changes phases quickly and unpredictably.

    The 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 during a negative phase.

    In New Zealand, the positive phase of IPO is linked to stronger west to southwest winds. The phase shift in 1976–7 led to more westerly winds in New Zealand over the subsequent two decades. 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).

    The index is based on anomalies in Pacific Ocean sea-surface temperatures. To account for changes in climate, global average sea-surface temperatures are considered in the index. Parker et al (2007) provide more information on the IPO.

    Data quality

    We classified Interdecadal Pacific Oscillation as supporting information.


       This supporting information is a partial measure of the ‘Natural pressures’ topic.


       The accuracy of the data source is of high quality.

    See Data quality information for more detail.


    Met Office Hadley Centre for Climate Change (2016). Interdecadal Pacific Oscillation time series. Retrieved from

    NIWA (nd). Past climate variations over New Zealand. Retrieved 17 July 2017 from

    Parker, D, Folland, C, Scaife, A, Knight, J, Colman, A, Baines, P, & Dong, B (2007). Decadal to multidecadal variability and the climate change background. Journal of Geophysical Research (Atmospheres), 112(D18), D18115.

    Zhang, Y, Wallace, JM, & Battisti, DS (1997). ENSO-like interdecadal variability: 1900–93 (PDF, 1MB). Retrieved from

    Archived pages

    See Interdecadal Pacific Oscillation (archived October 2017).

    Updated 19 October 2017

  • Share this page
  • Share this page to Facebook
  • Share this page to Twitter
  • Share this page to Google+