Decadal Variability in the North Pacific: The Eastern North Pacific Mode*

Decadal variability in the North Pacific is studied in a series of coupled global ocean–atmosphere simulations using coupled modeling surgery—a set of modeling approaches that can be used to identify the origins and causes of a specific variability mode in the coupled climate system. Both modeling and observational studies suggest two distinctive internal modes in the North Pacific: the North Pacific mode (NPM) and the eastern North Pacific mode (ENPM). The ENPM originates from atmospheric stochastic forcing through spatial resonance. Both local ocean–atmosphere coupling and remote tropical teleconnective forcing can enhance the ENPM, but none of them is a necessary precondition. The influence of the tropical forcing in the midlatitudes is dominated by atmospheric teleconnection, while the oceanic teleconnection is negligible. The upper-ocean heat budget reveals that SST anomalies in the central North Pacific and the eastern North Pacific are generated by anomalous Ekman advection and surface heat flux, respectively. In contrast to the ENPM, the NPM critically depends on local ocean–atmosphere coupled feedback, although the atmospheric stochastic forcing can generate a NPM-like mode with much reduced amplitudes and no preferred timescale.