Seasonal Variation in Volume Transport of the Kuroshio South of Japan

Abstract

Abstract A two-layer numerical model driven by the observed wind stress compiled by K. Kutsuwada and T. Teramoto is used to study the seasonal variation in volume transport of the Kuroshio south of Japan. The authors focus on the observational evidence that the geostrophic volume transport of the Kuroshio is maximum in summer and minimum in winter; however, Sverdrup transport estimated by the observed wind stress indicates a maximum in winter and a minimum in summer. It is shown from a flat-bottom model that the western boundary current has a maximum transport of 90 Sv (Sv ≡ 106 m3 s−1) in late winter and a minimum transport of 40 Sv from summer to early autumn. The time lag of the calculated transport from Sverdrup transport is about one month, which shows that the barotropic response is dominant for the seasonal change in wind stress. However, the vertical velocity difference at the western boundary region reaches a maximum in summer and a minimum in autumn, of which the summer maximum coincides with th...