Brody, The PDO is defined as the first EOF of SST anomalies north of 20N in the Pacific Ocean. If I do that analysis, the second mode is the NPM. This is discussed in my GRL article. Check out the supplementary materials in GRL, if you can find them. The NPM has a vaguely similar shape to the PDO, but is actually orthogonal to it. The shape of the NPM is closer to that of the Atlantic Multi-Decadal Oscillation, and is associated with the north-south dipole structure in the height field. What I show in the paper and this blog are the EOF's for SST anomalies north of 30S in the Pacific. In that case, for the recent data since 1979, the NPM is the second EOF and ENSO is the dominant first EOF. You do see some cold SST anomalies in the eastern equatorial Pacific, but I am not sure if that is critical to the primary nature of the mode, or just the EOF analysis trying to span the data as best it can. As a side note, one can now question whether doing analysis for the region north of 20N makes sense, since we know that the SST anomalies there are strongly driven from the tropics. A school of thought would say that the PDO is just the low frequency signature of ENSO in the North Pacific. If so, why not include the tropical Pacific in your thought process from the outset?