Decadal Variability in the North Pacific as Simulated by a Hybrid Coupled Model

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Abstract
In this study, a hybrid coupled model (HCM) is used to investigate the physics of decadal variability in the North Pacific. This aids in an understanding of the inherent properties of the coupled ocean–atmosphere system in the absence of stochastic forcing by noncoupled variability. It is shown that the HCM simulates a self-sustained decadal oscillation with a period of about 20 yr, similar to that found in both the observations and coupled GCMs. Sensitivity experiments are carried out to determine the relative importance of wind stresses, net surface heat flux, and freshwater flux on the initiation and maintenance of the decadal oscillation in the North Pacific. It is found that decadal variability is a mode of the coupled system and involves interaction of sea surface temperature, upper-ocean heat content, and wind stress. This interaction is mainly controlled by the wind stress but can be strongly modified by the surface heat flux. The effect of the salinity is relatively small and is not necessary to generate the model decadal oscillation in the North Pacific. There are some limitations with this study. First, the effect of a stochastic forcing is not included. Second, a weak negative feedback is needed to run the control experiment for a longer time period. These two areas will be addressed in a future investigation.

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