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HOME > El Niño Monitoring > Pacific Decadal Oscillation (PDO) index

Pacific Decadal Oscillation (PDO) index

Highlights

The Pacific Decadal Oscillation (PDO) index value for winter 2014 (December 2013 - February 2014) was -0.2. Focusing on the decadal variability of this index, positive values were generally observed from the late 1970s to 1990s, and negative values have generally continued since around 2000.


PDO index time series

The bars represent winter (DJF) mean values for the PDO index. The green line represents five-year running mean values of winter means. Data years refer to, for example, winter 2010 (December 2009 - February 2010) for "2010".



Explanation

The Pacific Decadal Oscillation (PDO) is an SST anomaly pattern of Pacific climate variability that shifts phases on an inter-decadal time scale usually covering more than 10 years. The PDO index is defined as the projections of winter mean SST anomalies onto their first EOF vectors in the North Pacific (north of 20ºN). Globally averaged monthly mean SST anomalies are subtracted from each monthly mean SST anomaly before calculation of the first EOF vector in order to eliminate the effects of global warming.

When the PDO index is positive (negative), SSTs in the central part of the North Pacific are likely to be lower (higher) than their normals (i.e., typical SST anomalies in the positive phase of the PDO). In addition, when the index is positive (negative), sea level pressures (SLPs) values in the high latitudes of the North Pacific are likely to be lower (higher) than their normals. This indicates that the Aleutian Low is stronger (weaker) than its normal in winter and spring (typical SLP anomalies in the positive phase of the PDO).

The Pacific Decadal Oscillation (PDO) index value was -0.2 for winter 2014 (December 2013 - February 2014).
Focusing on the decadal variability of the PDO index, its values varied from positive to negative during the 1940s and from negative to positive during the late 1970s, and were generally positive until the 1990s (the positive value corresponds to the pattern in which SSTs in the central part of the North Pacific are lower than their normals). Since around 2000, negative values have generally continued.


Explanation of Pacific Decadal Oscillation (PDO)
North Pacific Index
Monthly PDO index
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