CONCLUDING REMARKS
We found two distinct interdecadal modes of the coupled atmosphere-upper ocean temperature variability concurrently appearing in the Pacific Ocean of the AOGCM. The modes have spatio-temporal structures coherent to the observed SST variability. The first mode accompanies an ENSO-like spatial pattern for the SST and the surface wind, but their latitudinal extent is broader compared to that for ENSO. The temporal evolution of this mode behaves like a delayed oscillator in ENSO. Westward propagating trans-Pacific signal in the subtropical upper thermocline temperature appears to determine the timescale for the first mode.
The second mode is characterized by a midlatitude-subtropical dipole pattern of the upper ocean temperature which rotates clockwise around the North Pacific subtropical gyre. The temperature anomaly at the sea surface, which is reinforced by the aimospheric forcing around the Kuroshio Extension region, is subducted into subtropical subsurface layer along isopycnal surface, and is reinforced again in the southern branch of the North Pacific subtropical gyre in response to the associated wind forcing. The consequent variation of meridional heat transport works as a positive feedback to the midlatitude SST in the second mode. We propose that the second mode is excited by stochastic atmospheric forcing with spatial pattern associated with inherent variability of the atmosphere, while its timescale is selected by the ocean which has the interdecadal timescale associated with the clockwise rotation of the temperature anomaly around the North Pacific subtropical gyre.
These modes have some features in common with the interdecadal variation in other coupled models (cf. Latif and Barnett 1994, Knutson and Manabe 1998), but there are many differences among them.
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