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NASA image of the Pacific Ocean in April 2008 showing La Niña and Pacific Decadal Anomalies.

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 the results in 1997.[1]

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.[2]

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 El Niño-Southern Oscillation (ENSO).

Contents

Regime shifts

Observed monthly values for the PDO (1900–present).
 
Reconstructed PDO (1660–1991).

Although there are several patterns of behavior, the most significant one seems to be in regime shifts between "warm" and "cool" patterns which last 5 to 20 years [1].

  • 1750: PDO displays an unusually strong oscillation.[2]
  • 1905: After a strong swing, PDO changed to a "warm" phase.
  • 1946: PDO changed to a "cool" phase. [See the blue section of the graph on the right]
  • 1977: PDO changed to a "warm" phase.[3]
  • 1998: PDO index showed several years of "cool" values, but did not remain in that pattern.[4]
  • 2008: The early stages of a cool phase of the basin-wide Pacific Decadal Oscillation.[5]

In all cases in the 1900s, PDO "regime shifts" were related to similar changes in the tropical ocean.


Related patterns

  • ENSO tends to lead PDO/IPO cycling.
  • Shifts in the IPO change the location and strength of 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.
  • Sea level rise is affected when large areas of water warm and expand, or cool and contract.

References

  1. ^ Mantua, Nathan J.; et al. (1997). "A Pacific interdecadal climate oscillation with impacts on salmon production". Bulletin of the American Meteorological Society 78: 1069–1079. doi:10.1175/1520-0477(1997)078<1069:APICOW>2.0.CO;2. http://www.atmos.washington.edu/~mantua/abst.PDO.html.  
  2. ^ a b Biondi, Franco; Gershunov, Alexander; Cayan, Daniel R. (2001). "North Pacific Decadal Climate Variability since 1661". Journal of Climate 14 (1): 5–10. doi:10.1175/1520-0442(2001)014<0005:NPDCVS>2.0.CO;2. http://www.ngdc.noaa.gov/paleo/pubs/biondi2001/biondi2001.html.  
  3. ^ Hare, Steven R.; Mantua, Nathan J. (2000). "Empirical evidence for North Pacific regime shifts in 1977 and 1989". Progress In Oceanography 47 (2–4): 103–145. doi:10.1016/S0079-6611(00)00033-1.  
  4. ^ Hare, Steven R. (July 6, 2004). "Home Page for material relating to possible post-1977 regime shift". http://www.iphc.washington.edu/Staff/hare/html/decadal/post1977/post1977.html.  
  5. ^ Buis, Alan (April 21, 2008). "Larger Pacific Climate Event Helps Current La Nina Linger". NASA JPL. http://www.jpl.nasa.gov/news/news.cfm?release=2008-066.  

Further reading

External links

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