Pacific Decadal Oscillation Index


A study of the long period baroclinic variability in the Northeast Pacific Ocean (Cummings and Lagerloef, 2004) concludes that this variability occurs as a response to stochastic atmospheric forcing. They report that a significant percentage (~40%) of this variability is evident in the first EOF mode of a Markov model driven by local Ekman pumping as well as the first EOF mode of the Topex/Poseiden/Jason Altimeter representing the SSH. This suggests an EOF analysis of the altimeter data can be used as a useful indicator of this variability. This is consistent with previous studies of dynamic height anomalies over the Gulf of Alaska (Lagerloef, 1995), spectra of sea surface temperature and salinity (Hall and Manabe, 1997), and a long time series of pycnocline depth anomalies at Station P (Cummings and Lagerloef, 2002).

As a method of monitoring this variability, we present the spatial EOF pattern and amplitude of the first EOF of the T/P/J altimeter SSH anomaly (from the long-term mean) along with other North Pacific variability indices, for comparison. The PDO SST index (Mantua, 1997, is portrayed as blue and red bars, and the dynamic height anomaly (Lagerloef, 1995), is scaled with a factor of 3.5 - the black line. The SSH anomaly EOF is included as the green line. This and the PDO index are updated monthly.

Please contact John Gunn with questions or suggestions.





References

Cummins, P. , Lagerloef, G.S.E., and G. Mitchum, 2005. A regional index of northeast Pacific variability based on satellite altimeter data, Geophys. Res. Lett., 32, L17607, doi:10.1029/2005GL023642.

Cummins, P. and G. Lagerloef, 2004. Wind-driven interannual variability over the Northeast Pacific Ocean, Deep Sea Res. I, 51, 2105-2121.

Cummins, P. and G.S.E. Lagerloef, 2002. Low frequency pycnocline depth variability at Station P in the northeast Pacific, J. Phys. Oceanogr., 32, 3207-3215.

Hall, A., and S. Manabe, 1997. Can local linear stochastic theory explain sea surface temperature and salinity variability? Climate Dynamics, 13(3), 167-180.

Lagerloef, G., 1995. Interdecadal variations in the Alaska Gyre, J. Phys. Oceanogr., 25, 2242- 2258.

Mantua, N.J., S.R. Hare, Y. Zhang, J.M. Wallace, and R.C. Francis, 1997. A Pacific decadal climate oscillation with impacts on salmon. Bulletin of the American Meteorological Society, Vol. 78, pp 1069-1079.