Observations of Flow Dynamics in Kaoping Submarine Canyon

• Main Authors: Yu-Ga Chang, 張育嘉
• Other Authors: Ruo-Shan Tseng
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/84407131661814387614

碩士 === 國立中山大學 === 海洋資源學系研究所 === 89 === In order to better understand the flow dynamics of the Kaoping Submarine Canyon (KSC), this study conducted a series of field experiments to monitor the current, temperature, salinity and tide near the KSC by using shipboard ADCP, CTD and moorings of RCM-8 and workhorse ADCP. Three cruises of Sb-ADCP and CTD have been carried out in September and December of 1999 and May 2000, each lasting two days, while mooring experiment was conducted in June and July, 2000. Least-square fit was applied to the time series Sb-ADCP data of each grid to derive the amplitude and phase of M2 tidal current and the residual flow in the KSC. Our results revealed that a string baroclinic flow field was present in the KSC. Tidal ellipse of the bottom current is dominated by M2 component, with higher M2 percentage in deeper layers. The major axis of the tidal ellipse is parallel to the direction of the canyon axis. In floods, the bottom layer flows down-canyon and the surface layer flows southeastward along the coastline. In ebbs, the situation is reversed. Variations of the temperature and salinity in the bottom layer also exhibit periodic oscillation of the M2 frequency. Daily temperature fluctuation in summer can reach 8 oC, indicating the existence of internal tide in the KSC. The surface residual current flows toward the south east in September and May, with a maximum speed of approximately 30 and 50 cm/s, respectively; the result is probably due to the bifurcation of the summer monsoon flows by the southwestern coastline of Taiwan. In December the surface residual current is northwestward, the maximum speed can reach 80 cm/s. Such a northward mean flow is probably originated from branching of the Kuroshio through Bashi Channel in the winter monsoon season. To summarize, mechanisms for the upwelling event in the KSC consist of surface flow direction, tidal range, and the stratification. The upwelling event occurs more often in the KSC between May and September with the surface mean current flows southeastward or left-bounded. In December when the surface mean current flows northwestward or right-bounded, the upwelling event is rare. An eddy structure of 7 ~ 9 km length scale was observed north of Liu-Chiu Yu, a result possibly produced by Karman vortex street for strong geophysical flows behind an island.