･ Jan. 5: The SCCs' cores exist in shallow depth and near the EUC (3°N, 250m for the NSCC). There is cyclonic eddies on either side of the equator with the center near 4°latitudes and the eastward current component in the equator side of the eddies contribute to the SCC.
･ Jan. 5 to Jan. 15: The positions of the cores become deep and move to the poleward. In this stage, the cyclonic eddies propagate westward through this section and anti-cyclonic eddies with the center near 4° latitudes are coming from the east.
･ Jan. 15: The cores take the deepest and the most poleward positions (5°N, 300m for the NSCC) associated with the anti-cyclonic eddies.
･ Jan. 20 to Jan. 30: The cores move to the equatorward and become shallow. The SCCs become the lobs of the EUC on Jan. 30.
The variations are nearly symmetric on the equator, relate to the westward propagation of eddies anti-symmetric on the equator. The period of this fluctuation is about 30 days and the TIWs are found to affect the subsurface layers as well as surface layer.
Reynolds stress or eddy momentum transfer is computed to investigate the eddy effect on the mean SCCs. Fig. 6 shows negative Reynolds stress (＜ p0u'v'＞) or northward transfer of eddy eastward momentum on the isopycnal 26.5δθ. The eddy eastward and northward velocities (u', v') are defined as the anomalies from annual averaged velocities, and the period of time mean represented with the bracket ＜＞ is one year. There is positive ＜ p0u'v'＞ area around the equator, representing that the eastward momentum is transferred from the equator to the north. The annual averaged velocity vector overlaid on this plot shows the NSCC along 4°N, which latitudes corresponds to the northern boundary of positive ＜ p0u'v'＞ area. The eastward momentum is advected from the equator and converged along about 4°N. This result suggests that the eddy momentum transfer plays an important role on the maintenance mechanism of the NSCC.
5. Concluding Remarks
In this study we have described mean and variability of ocean circulation simulated in the high-resolution GCM developed at JAMSTEC, especially the SCCs comparing with the observation.
The model mean features is quite similar to the observation, especially for the SCCs; (a) the SCCs are associated with the pycnostad between 26.0 and 26.8δθ, (b) deep and week in the west and shallow and strong in the east, (c) the densities in the SCCs' cores show decreases to the east. However, the latitude of the model NSCC's core exist along nearly constant latitude about 4°N in almost entire basin and does not shift poleward from west to east. Zonally propagating eddies, whose signals are strong in the model subsurface as well as surface layer, may mix the latitudinal variation of the SCCs. The longitudinal variation of densities of the SCCs' cores is slightly larger than the observed estimates, therefore, the SCCs cross more isopycnals. Vertical mixing or diapycnal mass exchange may need to be considered to the dynamics of the mean structures of the SCCs.
It is found that there is a prominent temporal variability in the subsurface associated with the TIWs. The NSCC migrates between the EUC and NECC according to the westward propagation of the TIWs. The migration of the SSCC is symmetry to that of the NSCC with respect to the equator. There is strong eddy activity which transfer the eastward momentum from the equator to the north and converge near the NSCC core in the central and eastern equatorial Pacific Ocean.
