Different Scale Motion Characteristics Of The Northwest Slope Of The South China Sea Area

According to the ocean current observation and the satellite date from a moored Acoustic Doppler Current Profilers (ADCP) system on the northwest continental slope of South China Sea (SCS) as long as three months, this dissertation is intended to analyze the internal tides, eddy, steady flow as well as the motive characteristics of different scales of the northwest continental slope of SCS, explore the interaction of different scale motions, especially the influence of the eddy on the near inertial motion and internal tides, and also analyze the influence of typhoon on the upper ocean in terms of a certain typhoon process.The frequency spectrum identify than tides in this place are with the diurnal tides as the major, and the semi-diurnal tides as the minor. The K1, M2 amplitudes of the baroclinic tides first decrease, then increase as the depth changes and stay a greater value near the sea bottom. In the light of a simple two-dimensional model of internal tides, it is discovered that the baroclinic semi-diurnal tides under the topography of this place has formed reflection so that semi-diurnal tides has the obvious uploading energy.On the basis of the satellite observation of the ocean surface depth irregularity, it is found that there existed a warm eddy and a cold eddy in this place before and after the observation respectively and mainly influenced the upper ocean steady flowwhile the middle and deep steady flow variation might primarily have something to do with the SCS west boundary jets controlled by the monsoon as well as the topographical oppression of this place.Through the study of the near inertial energy variation during the period of mesoscale eddies, it reveals that the anti-cyclone eddy (warm eddy) facilitates the downloading of near inertial energy and the maximum near inertial energy depth emerges in the bottom of thermocline, while the cyclone eddy (cold eddy) constrains the downloading of the near inertial energy so that most of the near inertial energy is limited to the mixed layer, in which strong shear and turbulent mixing emerge, leading to the temperature dropping in mixed layer during the period of cold eddy larger than that during the period of warm eddy. The reason of the discrepancy lies in that the emergence of the background vorticity changes the available coriolis parameter fe = f+ξ/2, then changes the lower bound of the near inertial waveband that could be downloaded. In warm eddy, when f e decreases, the downward near inertial waveband becomes wider, the near inertial energy could more easily spread from the mixed layer to the thermocline. However, the positive vorticity of cold eddy raises the lower bound of the near inertial waveband that could be downward so that there is smaller downward near inertial waveband and most of the near inertial energy clusters in the mixed layer, and induces strong shears and mixing.Due to the typhoon Xangsane, the ocean surface temperature in the middle part of SCS dropped about 5℃, and the right path of it was influenced more strong. The slower the typhoon moving speed, the larger the energy transmitted by it to the ocean is, resulting that the entrainment of the mixed layer to the lower cold water becomes more intensive and the temperature dropping more prominent. The near inertial energy is transmitted by the typhoon to the bottom of the ocean in the form of near inertial internal wave. It always goes along with quite strong shear and mixing. As the near inertial energy gradually weakens, the influence exerted by it might continue one weeks or more.