On the Dynamics of Kuroshio Path Shifts near the Luzon Strait

Previous observations and simulations have revealed that, the westward shifts of Kuroshio path near the Luzon Strait (LS) are more common in winter. In this study, an ideal numerical model is used to demonstrate that, the Potential Vorticity (PV) input by the northerly wind stress in winter on the surface of non-uniform bathymetry in the Luzon Strait is the main dynamic mechanism of the Kuroshio intrusion into the South China Sea (SCS). According to PV dynamical theory, when the PV input by wind stress is positive, the water will be pushed to the higher PV region, while the PV input by wind stress is negative, the water will be pushed to the lower PV region. As the water depth (H) in the LS is smaller than that in the SCS to the west and that in the Pacific Ocean to the east, the planetary PV (f/H) in the LS is larger than both the west and east sides. When the north wind is prevailing in winter, as the zonal difference of the bathymetry, the PV input by wind stress [curl(tau/H)] is negative to the west of the LS, and positive to the other side. Thus it will push the water in western LS to the lower PV region, and the water in eastern LS to the higher PV region, so the whole water column around the LS will shift westward. When the south wind is prevailing in summer, the PV input by wind stress is positive to the west of the LS, and negative to the other side. Thus it will push the water in western LS to the higher PV region, and the water in eastern LS to the lower PV region, so the whole water column around the LS will shift eastward. Consequently, the Kuroshio intrusion into the SCS is more likely to occur in winter, which is demonstrated by numerical experiments.