Properties of Large-amplitude Internal Solitary Waves in the Sand-Dune Area on Upper Continental Slope of Northern South China Sea

• Main Authors: Chen-Hao, Hsueh, 薛成皓
• Other Authors: YIING JANG YANG
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/9a6f6g

碩士 === 國立臺灣大學 === 海洋研究所 === 106 === 　　In the northern South China Sea, the internal solitary wave (ISW) is extremely active and has the largest amplitude (> 150 m) in the world. The ISWs generate from tidal forcing on the ridges in the Luzon Strait, propagate northwestward, and traveling across the deep basin to the continental shelf. There are a few very large subaqueous sand dunes distribute on the upper continental slope and the ISWs could passage these sand dunes. According to the multi-beam bathymetry survey, the amplitude of sand dunes were about 10 m and crest-to-crest wavelength were about 300 m. These sand dunes could influenced the aspects of ISW. Five temperature and current velocity moorings deployed in the sand-wave area on the upper continental slope in June 3-19, 2014, which was contain a spring/neap tide period in order to investigate the properties of ISWs in this area. The transect of these moorings was almost parallel to the slope and the length of mooring array was about 13 km from local depth 380 m to 260 m. In traditional method, the average phase speed of ISWs could be estimated by the arrival time and the distance between different moorings. However, the directions of the ISWs were not parallel to the mooring transect, and therefore the phase speed estimated from arrival time could overestimated. Based on the DJL theory, using the temperature and current profiles observation data to estimate properties of ISWs including vertical displacement, instantaneous phase speed, direction, and energy flux. Moreover, based on Thorpe scale, the turbulence kinetic energy dissipation rates are estimated from shipboard CTD data by Thorpe scale. The total energy of ISWs reduce about 60 % and the average dissipation reach about 21.8 W/m2 and the average dissipation rate is about 6.2×〖10〗^(-5) W kg-1 in water depth from 286 m to 342 m which is relatively flat. However, the total energy of ISWs change insignificantly in water depth from 342 m to 262 m which is the steepest part of experimental area. The dissipation rate in the sand-wave continental slope is about 600 times as Dongsha plateau. It may because of the shoaling and the large subaqueous sand dunes. Moreover, the peak turbulence kinetic energy dissipation rate occur at the trailing edge of the apparent core, with the value of 6×〖10〗^(-5). Forty minutes later, the turbulence kinetic energy dissipation rate was small.