On the Variation of the Kuroshio Path South of Japan
Yoshihiko Sekine
Faculty of Bioresources, Mie University
The Kuroshio south of Japan shows a clear bimodal path between non-large meander path (nLMP) and large meander path (LMP). Variations in the Kuroshio is discussed with reference to difference in current path, seasonal variation in current velocity and volume transport, and sea level change at Kushimoto and Uragami, of which difference shows the periods of nLMP and LMP.
Variation in the Kuroshio path is examined by use of the observational distance of the main Kuroshio path from Japanese Coast. It is pointed out that LMP formed in 1975 has a larger distance from the Japanese coast and locates at south of Kii Peninsula, while some LMP formed after 1981 have smaller amplitude and locates at west of the Izu Ridge. It is shown that the pattern of LMP is quite different before and after 1980.
The observed geostrophic volume transport of the Kuroshio takes maximum in summer and minimum in winter, however, Sverdrup transport estimated from the observed wind stress takes maximum in winter and minimum in summer. It is resulted from a numerical model that the barotropic response is dominant for the seasonal change and the Kuroshio has a maximum transport in late winter and a minimum transport from summer to early autumn. However, the vertical velocity shear becomes maximum in summer and minimum in autumn, of which summer maximum coincides with the observed geostrophic transport. Development of the baroclinic response mainly formed by the strong winter wind stress is detected in summer. From these results, existence of a vertically homogeneous barotropic flow with large volume transport is suggested in winter along the eastern continental slope off Nansei Islands.
Difference in sea level between Kushimoto and Uragami locating at the tip of the Kii Peninsula is relatively large in periods of nLMP in comparison with that in LMP, which has been used as an good index of the periods of nLMP and LMP. Warm Kuroshio water has a tendency to approach to eastern (western) coast of Kii Peninsula in periods of LMP (nLMP). It is shown that the sea level change estimated by the vertical integration of the specific volume due to either approach of the warm Kuroshio Water agrees with those of the sea level difference between Kushimoto and Uragami. It is concluded that the clear relationship is caused by the thermal expansion due to the either approach of the warm Kuroshio water separated from mean flow of the Kuroshio.
