Division rate of the volume transport between the Tsugaru Warm Current and the northward Tsushima Current

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Numerical study, research cruise and data analysis have been made in order to understand the physics of the circulation in the Japan Sea and the division rate of the transport of the Tsushima Current between the Tsugaru Warm Current and the northward Tsushima Current. It is found by the numerical study that the circulation in the Japan Sea has a clear seasonal cycle : the wind-driven circulation is dominant in winter whereas the circulation excited by the in- and outflow through the three straits is dominant in summer. It is suggested that the depth of the current relative to the bottom west of Aomori Prefecture might be responsible for the division rate of the transport.Observations of the transport of the Tsugaru Warm Current by ADCP show a very distinct diurnal variation, which is shown to be caused by the sea level difference or pressure gradient along the down stream direction. The mean transport of 1.3 Sv is found to be in good agreement with another value of 1.4 Sv estimated from the balance of geostrophic volume transports along the CTD sections west off Aomori Prefecture and southern Hokkaido.Transport estimations by Ohtani et al. (1989)are analyzed together with sea level observations to find that the transports of the Tsugaru Warm Current and the northward flow aie in proportion to the downward sea level differences. This leads to a conclusion that division rate of the transport between the two currents is determined by the ratio of the sea level difference along the Tsugaru Strait to that along the western coast of Aomori Prefecture and southern Hokkaido.