東海大学紀要海洋学部　第48号　193-207頁　(1999)

駿河湾口東部における係留式上向きＡＤＣＰによる流動観測

Current Observation Using a Moored Upward-Looking Acoustic Doppler Current Profiler at the Eastern Part near the Mouth of Suruga Bay

勝間田高明・稲葉栄生・川畑広紀

Takaaki Katsumata, Hideo Inaba and Koki Kawabata

Abstract

Current observation by using a moored upward-looking Acoustic Doppler Current Profiler (ADCP) was carried out from July 6 to October 19, 1990 to investigate the temporal structure of current in the sea at eastern part near the mouth of Suruga Bay. Change of the northward current component was dominant throughout the entire observed layers (20 m - 220 m), associated with frequent reversals of current direction, namely inflow or outflow. As seen from the spectral analyses of currents the predominant periods shallower than about 75 m level and deeper than that level are 21-day and 18-day, respectively. Vertical structure of the current was represented by the empirical orthogonal function (EOF) modes. The first EOF mode contributing about 73 % of the total variance had no nodes, means that the currents at entire observed layers change with the same phase. As seen from the spectral analysis of score for the first EOF mode the predominant change has the period of about 20 days. The 20-day period was also found at the sea levels in the bay, i.e., Tago, and off the bay, i.e., Kozushima, Miyakeshima and Hachijoshima. It was found from the cross correlation function for those sea levels that the phase of peaks at those sea levels seems to travel from Hachijoshima to Tago with about 18 cm/sec. Therefore, the change of the 20-day period for the observed current in the bay mouth can be related to frontal wave of the Kuroshio off the bay. The secondary EOF mode contributing about 22 % had a node at about 110 m, meaning that the upper and lower currents change with an out-of-phase relation. A maximum of the score occurred almost synchronously with the passage of Typhoon - 9019, which suggests the out-of-phase relation can be caused by effect of the typhoon.

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