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

North Pacific Index (NPI)

NPI time series

The bars represent five-month mean ( November - March ) NPI values. The green line represents five-year running means of five-month mean NPI values. Positive (negative) NPI values indicate that the Aleutian Low is weaker (stronger) than its normal. For comparison with the PDO index, the period of the graph is adjusted to that of the PDO index.


Trenberth, K. E. and J. W. Hurrell, 1994: Decadal atmosphere-ocean variations in the Pacific. Clim. Dyn., 9, 303 - 319.

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