Localized North Pacific decadal variability

Sea surface temperature (SST) variability has a notable maximum in the North Pacific. This variability is associated with both local and large-scale modes, including the Pacific Decadal Oscillation (PDO) and both mature and transition phases of the El Nino - Southern Oscillation (ENSO). In addition to the activity of several spatial patterns, the variability spans a wide range of time scales, including interseasonal, interannual, and decadal.

In order to extract the decadal scales of the local variability, several calculations are performed. The local variability is separated from thelarge-scale ENSO and PDO patterns via rotated principle component analysis (RPCA) on Pacific SSTs, which resolves all three patterns. A relationship to the transition phase of ENSO is not removed by this approach, however, since the transition ENSO pattern is so different from the mature pattern. This ENSO relationship is largely with the quasi-quadrennial component, and is removed via band pass filtering. Finally, a strong interseasonal variation is still present, and this is removed by isolating the high frequency oscillation via singular spectrum analysis and subtracting the result. What remains is largely the decadal variations associated with the local North Pacific SST variability. Using this time series, the global atmospheric teleconnections and associated diabatic heat structures are computed.

The interseasonal component of the variability is also further analyzed. Preliminary examination of ocean analysis data suggests that the decadal scale variability may be largely a modulation of the higher frequency variability, which is in the form of pulses of warmer or colder water in the upper ocean. These pulses appear to have a characteristic time of about one year but no clear connection to the annual cycle. The timing and vertical propagation of the pulses is also examined in the original bathymetric data.