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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).
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
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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.
- ^ 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
- LI Chongyin, HE Jinhai, ZHU
Jinhong (2004). "A Review of Decadal/Interdecadal Climate Variation
Studies in China". Advances in Atmospheric Sciences
21 (3): 425–436. doi:10.1007/BF02915569.
- C. K. Folland, J. A. Renwick, M.
J. Salinger, A. B. Mullan (2002). "Relative influences of the
Interdecadal Pacific Oscillation and ENSO in the South Pacific
Convergence Zone" (). Geophysical Research Letters
29 (13): 21–1–21–4. doi:10.1029/2001GL014201. http://www.niwa.cri.nz/ncc/icu/2002-10/article.
- 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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