Spring–neap tidal variations of residual flow in Tokyo Bay, Japan

Sea surface current observations with the use of two high-frequency radars were carried out near the mouth of Tokyo Bay, Japan from 1 December to 23 December 1998. A peculiar fortnightly variability of residual flow was found near the mouth of Tokyo Bay, that is, sea surface residual flow was weak and southward in spring tide but it was strong and formed a clockwise circulation in neap tide. Strong sea surface residual flow resulted from large vertical shears of estuarine circulation and small vertical viscosity by weak tidal currents in neap tide. The clockwise circulation was produced by an expansion of horizontal circulation from the river mouth to the bay mouth.