Geoscience Reference
In-Depth Information
PDO
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Figure 9.13
Typic a l
wintertime Sea Surface
Temperature (colors), Sea
Level Pressure (contours) and
surface wind stress (arrows)
anomaly patterns during
warm and cool phases of
Pacific Decadal Oscillation
(From http://jisao.
washington.edu/pdo/.)
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Warm phase
Cool phase
The opposite phenomenon when the SST in the eastern Pacific is colder than
average is called La Niña, which means 'the little girl. The east-west movement
in Pacific SSTs that occurs in El Niño and La Niña conditions necessarily results in
shifts in the position of maximum convection in the equatorial Pacific, and this in
turn gives rise to large-scale changes in the general circulation of the atmosphere.
By correlating the changes in regional climate at locations around the world that
are generated by such changes in atmospheric flow with observed fluctuations in
the SST in the tropical Pacific, statistical relationships have been developed that
can be used to make seasonal predictions in those regions when El Niño and
La Niña have influence.
Pacific Decadal Oscillation
The Pacific Decadal Oscillation (PDO) is a long-lived El Niño-like pattern of
Pacific climate variability, see Fig. 9.13. While the two climate oscillations are simi-
lar in that they have spatial climate fingerprints, they have very different behavior
in time. Two main characteristics that distinguish PDO from El Niño/Southern
Oscillation (ENSO) are:
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persistence
: during the twentieth century PDO events persisted for 20 to 30
years while typical ENSO events persisted for 6 to 18 months; and
location of impact
: the climate fingerprints of the PDO are most visible in the
North Pacific and North America with secondary signatures in the tropics,
but the opposite is true for ENSO.
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Several studies have found evidence for two full PDO cycles in the past century.
Cool PDO regimes prevailed from 1890 to 1924 and again from 1947 to 1976,
while warm PDO regimes dominated from 1925 to 1946 and from 1977 through
the mid-1990s and beyond.
