Observations of internal tides and cold-water intrusion in NanWan Bay

• Main Authors: Chih-ya Yen, 顏之雅
• Other Authors: Yu-Huai Wang
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/29069632390144350759

碩士 === 國立中山大學 === 海下科技暨應用海洋物理研究所 === 101 === Internal tides are generated, in a stratified ocean, as the tidal currents move over ridges, sills, continental slope etc. Internal tides may cause vertical mixing, which transfer heat from surface layer down to deeper interior. It may also entrain lower layer cold and nutrient rich water up to the near surface to fertilize the ecosystem. Cold-water intrusions in NanWan Bay were reported frequently, which can reduce the coral bleaching caused by the global warming. This study investigates the occurrence of internal tide and its associated effect in NanWan Bay. The data, mainly ADCP and CTD, used in this study were collected by OR1, OR2, OR3 during 1991 to 2008. An additional set of data by moored ADCP and vertical arrays of temperature loggers were applied. The selected data are screened through a variety of time series analysis technique, including harmonic, EOF and spectrum analyses etc. The results show that (1) upwelling is related to tide, and there are two cold water intrusions per day with different degree of intensity. (2) The time-depth flow data indicated there was an interface of opposite flow directions which coincide with temperature contours. The depth of interface decreases from outer bay toward the inner bay, indicating the elevation of internal tide. (3) The most energetic component of fluctuations were the diurnal (K1) and semidiurnal (M2) tides, however, there also were secondary peaks at 8hr and 6hr.The percentage of variance for the higher frequency are more than 10% of total variance. (4) The T-S diagram indicated that water mass of lower layer is SCS water, while the upper layer includes Kuroshio intrusion and fresh water dilution.