IPO = Interdecadal Pacific Oscillation
PDO = Pacific Decadal Oscillation
ENSO = El Nino-Southern Oscillation
According to Chris Folland of Hadley Centre,” The Interdecadal Pacific Oscillation (IPO) is (almost) the Pacific-wide manifestation of the Pacific Decadal Oscillation of Mantua et al (1997), with as much variance in the Southern Hemisphere Pacific down to at least 55oS as in the Northern Hemisphere. The IPO is a multidecadal sea surface temperature (SST) pattern quite like that of ENSO, but differing in several ways.” He concludes that opening paragraph in the following with, “The physical nature of the IPO is under investigation; it is still not clear, despite the above studies, to what extent the IPO is really independent of ENSO red noise and especially of SST variations near a decadal time scale.” The following link is also the source of the raw IPO data used in the following comparisons.
I’ve covered the PDO-ENSO relationship in a number of posts. At the end of the second of the following links is a quote from a paper that states, “The PDO is dependent on ENSO on all timescales.” It may also appear in the first link.
Also on the PDO: The three PDO data sets (JISAO, ERSST.v2, ERSST.v3) are discussed here:
IPO VERSUS PDO
If we assume the PDO is dependent on ENSO, is there enough of a correlation between the PDO and the IPO to assume that the IPO is also dependent on ENSO?
The following three graphs illustrate the correlation between the PDO and IPO. Figure 1 illustrates raw IPO and PDO data. Note: There aren’t 5 and 6 deg C basin-wide oscillations in the Pacific. The amplification of the signal is a result of the statistical process they use to extract the IPO from Pacific SST data. (The same note applies to the PDO, as well.) The PDO and IPO appear to have the same basin trends and perturbations.
In Figure 2, the IPO and PSO data was smoothed with a 37-month filter. Due to the additional statistical processes used to create the IPO, its scale differs from the PDO.
In the Figure 3, the IPO was scaled with a multiplier of 0.33 to highlight the correlation with the PDO. There are some minor variances, just as there are differences between the three PDO data sets.
IPO VERSUS ENSO
Figure 4 shows the relationship between the raw IPO and ENSO signals. The major perturbations in the IPO appear to result from ENSO. Refer to previous notes about the IPO scale.
When the data is smoothed with 37-month filters, Figure 5, the interrelationship between the IPO and ENSO is still visible.
Scaling the IPO, again with a multiplier of 0.33, illustrates the divergences between the two data sets. Refer to Figure 6. I ended the ENSO data early so that its time scale was the same as the IPO data. Considering the other processes taking place in the Pacific basin such as thermohaline circulation/meridional overturning circulation, I find the correlation remarkable.
Is the IPO dependent on ENSO? Yes, but it’s also effected by other variables that impact the North and South Pacific.
SOURCE OF EL NINO DATA
Data is Smith and Reynolds Extended Reconstructed SST (ERSST.v2) available through the NOAA National Operational Model Archive & Distribution System (NOMADS).