Numerical study on the Kuroshio path states in the northern Okinawa Trough of the East China Sea

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Previous observations have indicated that the Kuroshio in the northern Okinawa Trough is quasibimodal in character, with distinct northern and southern path states. The Kuroshio path states are examined here through simulations using a primitive inflow/outflow model for 16 inflow structures parameterized by the location of maximum surface velocity and the rate of velocity decrease with depth. The simulations reveal three distinct path states in the northern Okinawa Trough: a weakly stable northern path state associated with blocking of an anticyclonic Kuroshio meander, a highly stable southern path state maintained by blocking of a cyclonic Kuroshio meander, and an intermediate unstable path state. The variations in the unstable state, occurring as either periodic transitions between the northern and southern path states or periodic fluctuations of an otherwise stable path, are driven by self‐sustained internal oscillation in the northern Okinawa Trough. Cyclogenesis in the continental slope area due to baroclinic instability appears to play an important role in Kuroshio path variations in the unstable state, and this instability is effectively controlled by the location of the Kuroshio mean path on the slope rather than its velocity as conventionally thought.