KUROSHIO PATH VARIATION SOUTH OF JAPAN .1. BAROTROPIC INFLOW-OUTFLOW MODEL

We examined the dynamics of the variation in the path of the Kuroshio current along the south coast of Japan by use of a barotropic inflow-outflow ocean model. The model basin has an inclined coastline and includes a part of the East China Sea so that we could investigate the effect of Kyushu on the Kuroshio. We obtained three regimes of the Kuroshio's path variation according to the magnitude of its inlet velocity V(max), similar to the previous study. The Kuroshio takes a straight path along the south coast of Japan in regime I with a low V(max), a meandering path in regime II with a high V(max), and both of these paths (multiple-equilibrium state) in regime II with an intermediate V(max). The transition from the straight state to the meandering state occurs with an increase in V(max) from regime I (III) to II, preceded by an eastward progression of a small meander which is produced as a separated vortex by the nonlinear effect of the flow and the effect of Kyushu. It takes 120 days, consistent with observations. The nonlinearity of the flow has two effects in the transition. One causes a downstream shift of the small meander, and the other enlarges it by pulling out positive vorticity from the no-slip coast. With an increase in the meander scale due to the latter effect, the former effect becomes small to be balanced with the beta effect, causing an upstream shift of the meander. Thus a large-meander path is formed. A small meander does not progress eastward to develop into a large meander until V(max) exceeds a critical value. This behavior causes a multiple-equilibrium state in Regime III and only the meandering path in Regime II.