The Pacific Decadal Oscillation (PDO) is a long-term ocean fluctuation
of the Pacific Ocean. The PDO waxes and wanes approximately every 20 to
30 years. From TOPEX/Poseidon data (see below) together with other
oceans and atmospheres data, scientists think we have just entered the
'cool' phase. The 'cool' phase is characterized by a cool wedge of lower
than normal sea-surface heights/ocean temperatures in the eastern
equatorial Pacific and a warm horseshoe pattern of higher than normal
sea-surface heights connecting the north, west and southern Pacific. In
the 'warm' or 'negative' phase, which appears to have lasted from 1977-
1999, the west Pacific Ocean becomes cool and the wedge in the east
warms. Notice that the surface wind directions (arrows) tend to reverse
themselves in the two phases NASA
Figure: Pacific Decadal Oscillation.
(top) Typical wintertime sea surface temperature (colors), sea level
pressure (contours), and surface wind stress (arrows) anomaly patterns
during positive and negative phases of the Pacific Decadal Oscillation (PDO),
as derived from the TOPEX/Poseidon satellite plus other ocean/atmosphere
data. Temperature anomalies (colors) are in degrees Celsius. (bottom)
Monthly values for the PDO index, 1900-2004. Credit: S.
Hare and N. Mantua, University of Washington.
The PDO has a very good correlation with earth's
temperature. Note that the PDO (negative) warm phase dominated in the
1920s-1945 and 1975-1997 when the earth experienced record warming,
while the 1945-1975 period was dominated with the PDO (positive) cold
phase when the earth cooled. The PDO started to slip back into the cold
phase around 2000 and then warmed briefly to 2006. Although it is not
shown in this graph, the PDO has turned sharply cooler again in
2007-2008, where most scientists believe it will stay for the next 20 to
30 years. |
