Stable paths of the Kuroshio south of Japan determined by the wind stress field

To investigate the role of the wind stress field in determining stable paths of the Kuroshio south of Japan, we have executed numerical experiments with a two‐layer, wind‐driven ocean model, changing zonal and meridional wind stress distributions. Four types of path (two straight and two meandering paths) have been found, and their appearance has been classified into three categories. In category I, straight and meandering paths coexist (multiple equilibrium); only a meandering (straight) path appears in category II (III). A meandering path tends to appear when the Sverdrup transport along the southern coast of Japan decreases downstream strongly and the wind stress curl is anomalously negative in the western region near Japan, whereas a straight path is apt to occur with the positive anomaly. Detailed examination of the results has revealed the following mechanism determining stable paths of the Kuroshio. The wind stress field first determines the pressure difference Δp* between the two ends of the southern coast of Japan. When Δp* is smaller than a certain threshold, only a meandering path can exist since the along‐coast pressure decrease in a straight path state is much larger than Δp* (category II). Conversely, when Δp* is larger than another threshold, only a straight path is consistent with the larger Δp* (category III). Both paths can appear when Δp* is between the two thresholds (category I). The climatological wind stress field in the North Pacific subtropical region has been suggested to be in category I.