The cores' positions, velocities and transports of the SCCs
Longitudinal variations of latitudes, depths, potential densities, and maximum speeds of the model SCCs' cores and the transports of the SCCs are shown in Fig. 4 with the estimates from hydrographic observation at three longitudes (165｡?, 155｡?, 110｡?) by Johnson and Moore (1997), who estimate them from geostrophic computation referred to 700 db pressure. The currents' cores are defined as the positions of the maximum eastward velocity.
As seen in Fig. 3, the latitude of the NSCC is nearly constant compared with the observation which shows the poleward shift from 2.5｡? at 165｡? to 4.5｡? at 110｡?. For the SSCC, there are latitudinal gap in the central Pacific Ocean from about 160｡? to 120｡?, where the maximum speed of the poleward SSCC is larger than that of the equatorward side one. In the eastern Paciflc east of 110｡?, the model cores' latitudes shift equatorward from west to east. This may be caused by the existence of multiple eastward jets there. The most critical difference between the model and the observed estimate is that the poleward shift from west to east is not simulated in the model because the model cores exit poleward to the observed in the western Pacific Ocean. The model NSCC is originated in the northward bifurcation of the confluence of the EUC and the Equatorial Intermediate Current (EIC) around 143｡? north of the New Guinea (the figure is not shown). The origin of the model SSCC exist around 155｡?, 4｡? where the New Guinea Coastal Undercurrent bifurcates to the east. These results suggest that there are different mechanisms for the origins of the North and South SCCs.
The longitudinal variation of the depths and potential densities of the model SCCs simulate the observed feature, i.e., shoaling of depth and decrease in density from west to east. In the central Pacific from about 160｡? to 120｡?, there are the deeper depth and larger density of the poleward SCC core.
The transport of the SCCs is computed in the latitude bands from 3° to 6° and in the density range from 25.5δθ to 27.3δθ. The maximum speeds and transports of the model SCCs show roughly constant values (10cm s-1 for the NSCC, 5cm s-1 for the SSCC and 3 to 5 Sv for both the SCCs) in the western and central Pacific, but increase from west to east in the eastern Pacific Ocean. The maximum values are larger than 25cm s-1 and 8 Sv for the NSCC. Johnson and Moore (1997) estimated about 10 to 15cm s-1 and 4 to 6 Sv for the SSCC, 25 to 30cm s-1 and 7 Sv for the NSCC from geostrophic calculation. They noted that the NSCC transport estimate along 165°E was 10.3 Sv larger than those along the other sections because it included part of the transport of the NECC. The difference between the model and the observed estimates may be caused by the model deficiency, e.g., low resolutlon or weak variability forcing by climatologies. However, the observed estimates have wide range. Hayes et al. (1983) report 40cm s-1 14 Sv for the NSCC along 110°W. The maximum speed for the NSCC along 158°W is smaller than 15cm s-1 according to the figure shown in Wyrtki and Kilonsky (1984). The model results are not inconsistent with the observed estimates.
4. Variability of the SCCs
The model show remarkable variability associated with westward propagating waves of period of about 30 days and wavelength of about 1000km to 1300km in the central and eastern Pacific Ocean. The model sea surface temperature (SST) shows cusp-shaped pattern between the equator and 5｡?. These features are consistent with the observed variability of SST and currents known as the TIWs (e.g., Philander, 1990). In this section, we describe the variability of the model SCCs and the effects of the TIWs to the SCCs. The instantaneous distributions of the model eastward velocity are shown every 5 days from Jan. 5 to Jan. 30 along 155｡? in Fig. 5. It is found that the SCCs fluctuate in their positions between 2｡? and 6｡? with time.
