The coherent patterns between the tropical-to-Northern extratropical Pacific SST anomalies and the North Pacific 500-mb height (GPH) anomalies are obtained by using the conditional maximum covariance analysis. In this study, two leading modes are identified. One is an intrinsic midlatitude air-sea coupled mode (a.k.a. ‘North Pacific Mode’), which is generated by the mid-latitude stochastic behavior of the atmosphere. The other is a tropical ocean-atmosphere coupled instability mode (a.k.a. ‘ENSO Mode’), which in turn influence the North Pacific SST pattern through atmospheric teleconnection. In North Pacific mode, the atmosphere variation leads the changes in SST. In the ENSO mode, the changes in the tropical SST lead the atmospheric circulation over the whole Pacific so do the North Pacific SST anomaly.

In general, Spatial and temporal characteristics of NP mode are clearly distinguished from ENSO mode except a significant correlation between their expansion coefficient time series associated with GPH pattern. However, by reddening the time series, the GPH fluctuations of NP mode renders to be uncorrelated with that of ENSO mode. Thoroughly, we have confirmed that NP and ENSO modes are not only statistically but also physically independent. This independency between two modes is valid especially in the interannual time scale, but in the decadal-to-interdecadal time scale, the modal separation becomes more or less unclear.