Numerical Modelling On The Generation Process Of The Tidal Internal Waves Over The Northwestern South China Sea Shelf

Owning to its multifarious current motions and topographic features, SouthChina Sea is one of the most active areas for internal waves. Reports, observationsand researches up-to-date of internal waves in the South China Sea are mainlyfocusing on those distributing from the Luzon Strait to the Dongsha Islands. TheInstitute of Oceangraphy of the Chinese Academy of Science and the China NationalOffshore Oil Corp. performed a joint scientific investigation to the east of Hainan,started from April 16,2005 and lasted for nearly half a year at the Wenchang Station.The bathymetry data clearly indicate the existence of regular long-term internal waveson the shelf of this region.The information captured by shuttle or SAR indicates that some of the internalwaves in this region are not origined from Luzon Strait, but may generated by thebarotropic tidal flux interacting with bottom topography.We will prove this viewpointusing numerical modeling method in this article.Based on the governing system of Reynolds equations,we develop a twodimentional numerical model for the continuous stratified sea to simulate thegeneration process of internal waves by the tide-topography interaction.Differencemethod and finite-element method are used for this model. Generation process ofinternal waves excitated by barotripic tide flowing over typical topography (forinstance, the descending topography, ascending topography, raised topography andsunk topography) is studied. The influences of parameters on the generation processare also discussed.Then we extract such sea environment parameters as the density,thickness andintensity of the pycnocline out of the field data of Wenchang Station.Velocity,amplitude, direction and some other information of each component tides ofbarotropic tide fluid connected with the numerical method are separated form thecurrent flow using harmonic analysis method.Numerical simulation is carried usingthose sea environment parameters and information of each component tides into thenonlinear numerical model of internal wave generation at the continental slope nearWenchang Station.Result shows that the tide-topography interaction is strong enoughto generate large-amplitude internal waves that are visible on SAR images, whichsuggests that the tidal internal waves over the Northwestern South China Sea Shelfcan be generated by the barotropic tidal flux interacting with slope and then propagatsto the shelf.