The Residual Current Derived from Ship-board ADCP Measurements of East China Sea in June 1999

• Main Authors: Dee-Way Wang, 王迪慰
• Other Authors: Cho-Teng Liu
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/24565836741299631346

碩士 === 國立臺灣大學 === 海洋研究所 === 93 === In most shallow seas, the major components of ocean current are tides. To derive the residual low frequency current velocity, one usually deploys current meter moorings over 25 hours or more to remove the diurnal and semi-diurnal tidal components. Using ship-board ADCP (Acoustic Doppler Current Profiler) to derive the residual current, one may design ADCP measurements at different phases of tides at every location. The sum of these measurements cancels out the tidal component. But, most cruises are aimed at other goals, and ADCP measurements are only complementary data of the cruise. Here, we demonstrate a method for deriving the M2 and S2 tidal current and the mean current from a 14-day cruise in the East China Sea, June 1999. The basic assumption is that the tidal current varies smoothly in the region of survey. This assumption is valid as seen in many tidal models of East China Sea. The 1-min ADCP data were first averaged over 11 minutes to reduce data size, then averaged over 12.4 hours to derive the residual current that contains little M2 tidal component. Data over continental slope were deleted because of the influence of Kuroshio and the possibility of large gradient in tidal velocity. The residual current data were fitted with bi-linear spatial function to capture its main feature. The pattern of derived mean current matches those published earlier from mooring and drifter data. The semi-diurnal tidal current equals the total current minus the residual current which is 12.4-hour moving average of total current velocity. The co-phase and co-range line of the semi-diurnal tidal current are similar to those of model results of semi-diurnal tidal elevation and tidal current observation near cruise track. This provides a proxy proof of the reliability of this method.