Winter Transport and Tidal Current in the Tsugaru Strait

2 ), Abstract Transport variations and characteristics of tidal currents in the Tsugaru Strait are investigated using the ship­ mounted acoustic Doppler current profiler (ADCP) measurements from October 29, 1999 to March 31, 2000 along one line across the Strait. The Tsugaru Strait connects the North Pacific Ocean and Japan/East Sea, and is a main output for Tsushima Warm Current System in Japan/East Sea. The strong northeastwards mean current flows through this section approximately in the center of the Strait, and southwestward counter flows exist near both the Hokkaido and Honshu coasts. The estimated mean net eastward transport, i.e., the Tsugaru Warm Current transport, is 1.8 Sv (Sverdrup, I Sv= 10 6 m 3 s- I ). The data are analyzed four major tidal constituents, i.e., M2, S2, 01 and KI. Although the amplitudes of semi-diurnal tides are generally larger than those of diurnal tides, the amplitudes of KI and M2 volume transports across the strait are 0.72 Sv and 0.52 Sv, respectively, i.e., diurnal tidal currents are dominant. From the phase relationship between tidal volume transport and tide is understood with a composite of standing and incident Kelvin waves, which propagates from the North Pacific Ocean to the Japan/ East Sea. We also find a significant fortnightly oscillation which has a barotropic structure. The long-period lunar fortnightly (Mf) tide is more energetic along the coast faced on the Japan/East Sea with the amplitude of 1 ~3 cm, while the amplitudes for Mftide in the North Pacific Ocean are much smaller, less than 1 cm. It is inferred that observed fortnightly oscillation may be generated by the difference of Mf tide amplitude between both sides of the Tsugaru Strait.