Annual variation

Figure 5 shows the streamfunction every 60 days. Figure 6 shows the time series of the streamfunction at eastern and western edges of the ridge. The annual range of the calculated volume transport is nearly the same as that of the nontopographic Sverdrup transport east of the ridge because the flat bottom region extends east of the ridge. However, the annual range decreases drastically west of the ridge compared to that of the nontopographic Sverdrup transport at the same point. The signal of the time-dependent part of the volume transport is prohibited from crossing the ridge due to the topographic ƒÀeffect. As a result, the annually averaged part of the solution (steady-state solution) is dominant in the western portion of the ridge.

Although the annual range of the volume transport variation west of the ridge is much smaller than that of the Sverdrup transport there, volume transport varies in time slightly. Figure 7 shows the time series of the streamfunction at the western edge of the ridge; time series is the same as in Fig.6 except for the enlarged scale of the ordinate. Also shown is the time series of the volume transport calculated by a one-layer numerical model with the ridge driven by the same time-varying wind stress. In the one-layer model, only the variation with the annual range of about 3 Sv leaks to the west of the ridge. On the other hand, the annual range is about 10 Sv in the volume transport variation in the two-layer model. This means that the baroclinic activity amplifies the annual range of the volume transport. Figure 8 shows the y-t (distance from the southern sidewall-time) plot of the streamfunction along the western edge of the ridge. It is found that the phase is delayed northward.