Pacific decadal oscillation

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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 patterns. Simultaneously the PDO climate pattern was also found by Yuan Zhang. The two groups described the patterns in 1997 (Mantua et al., 1997).

The mechanism by which the pattern lasts over several years has not been identified; one suggestion is that a thin layer of warm water during summer may shield deeper cold waters. 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 SST and 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 to the quasi-decadal oscillation (QDO) with a period of 8-to-12 years and maximum SST anomalies straddling the equator, thus resembling ENSO.

Before 1977, "cool" PDO manifested as warm water in northwestern Pacific and cool along southern Alaskan coast.
Before 1977, "cool" PDO manifested as warm water in northwestern Pacific and cool along southern Alaskan coast.
Recent temperature changes, while PDO primarily in "warm" phase.
Recent temperature changes, while PDO primarily in "warm" phase.

Contents

[edit] Regime shifts

Although there are several patterns of behavior, the most significant one seems to be in regime shifts between "warm" and "cool" patterns which last 20 to 30 years.

  • 1750: PDO displays an unusually strong oscillation.
  • 1905: After a strong swing, PDO changed to a "warm" phase.
  • 1946: PDO changed to a "cool" phase.
  • 1977: PDO changed to a "warm" phase.
  • 1998: PDO index showed several years of "cool" values, but has not remained in that pattern. [1]

In all likelihood, these regimes shifts result from random noise processes. In all cases in the 1900s, PDO "regime shifts" were related to similar changes in the Tropical ocean.

[edit] Related patterns

  • El Niño (ENSO) tends to lead PDO/IPO cycling.
  • Shifts in the IPO change the location and strength of El Niño (ENSO) activity. The South Pacific Convergence Zone moves northeast during El Niño and southwest during La Niña events. The same movement takes place during positive IPO and negative IPO phases respectively. (Folland et al., 2002)
  • Interdecadal temperature variations in China are closely related to those of the NAO and the NPO.
  • The amplitudes of the NAO and NPO increased in the 1960s and interannual variation patterns changed from 3–4 years to 8–15 years.
  • The pattern of global warming during the past century changed to cooling during the 1946–1976 PDO "cool" regime.
  • Sea level rise is affected when large areas of water warm and expand, or cool and contract.

[edit] References

[edit] External links

[edit] Further reading

  • Steven R. Hare and Nathan J. Mantua, 2001. An historical narrative on the Pacific Decadal Oscillation, interdecadal climate variability and ecosystem impacts, Report of a talk presented at the 20th NE Pacific Pink and Chum workshop, Seattle, WA, 22 March 2001. [2]
  • Nathan J. Mantua and Steven R. Hare, 2002. The Pacific Decadal Oscillation, Journal of Oceanography, Vol. 58, p. 35–44. DOI:10.1023/A:1015820616384 [3]
  • Kevin Ho, 2005. Salmon-omics: Effect of Pacific Decadal Oscillation on Alaskan Chinook Harvests and Market Price. Columbia University. [4]
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