東海大学紀要海洋学部　第51号　63-88頁　(2001)

駿河湾口東部海域において係留式ＡＤＣＰにより観測された内部潮汐流

Internal Tidal Currents Observation with a Moored ADCP at Eastern Part of the Mouth of Suruga Bay

安田訓啓・稲葉栄生・川畑広紀・守屋洋・勝間田高明

Kuniaki Yasuda, Hideo Inaba, Koki Kawabata, Hiroshi Moriya and Takaaki Katsumata

Abstract

Current data obtained with moored Acoustic Doppler Current Profiler (ADCP) from July 6 to October 19, 1990 were used to investigate characteristics of tidal currents at eastern part of the mouth of Suruga Bay. The amplitude of observed tidal current is much larger than that expected by surface tide, suggesting that tidal current is caused by internal tide. Diurnal tidal current is mostly dominant compared with semidiurnal one except in surface layer. Vertical profiles of tidal constants and parameters of tidal ellipsis of diurnal tide current are rather simple with small temporal changes of the constants and parameters except for the amplitude in surface layer. The amplitude of diurnal tide current is large in surface layer and monotonously decrease with depth. The phase angle, the orientation of major axis of tidal ellipsis and the direction of rotating tidal current vector of diurnal tide current are uniform vertically. The major axis is nearly directed to shoreline .On the other hand, vertical profiles of tidal constants and parameters of tidal ellipsis of semidiurnal tide current are complicated with sharp changes of the constants and parameters in the entire observed layer. In the case of large amplitude both in two layers above 100m and below, the phase angle and the orientation of major axis in the lower layer are different from those in the upper layer. The major axis in the upper layer is nearly directed to shoreline as same as that of diurnal tidal ellipsis. The difference in vertical structure of the orientation of major axis of tidal ellipsis between diurnal and semidiurnal tidal current is related to that two different type of internal tidal wave can be propagating in Suruga Bay. Amplifications both ob diurnal and semidiurnal tidal currents in surface layer are caused by the internal tides propagating northward along the western coast of Izu Peninsula as coastal Kelvin waves. On the other hand, amplification of semidiurnal tidal current in the lower layer is caused by the internal tide propagating freely as inertio-gravity wave. It is suggested that the temporal change of tidal current amplitude is governed by the variation of density field near the station related to the long period variation of along-shore current caused by the fluctuation of Kuroshio off Suruga Bay.

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