Mechanisms Of Breaking And Mixing Induced By Internal Tidal Wave And Internal Solitary Wave In China Seas

Internal tidal waves (ITWs) and internal solitary waves (ISWs) are frequentlyobserved in China Seas. It is quite significant to study the nonlinear evolutionprocesses and the breaking and mixing phenomenon of ITWs and ISWs.In the first part of this paper, an elementary numerical simulation of nonlinearevolution of ITWs is made in the Yellow Sea, using the generalized KdV model(GKdV model for short) for continuous stratified ocean. It is found that, thebackground currents play a very important role in the propagation process of ITWsand ISWs. Distinguishing the different effect between the background ebb and floodcurrent is necessary, which is the advantage of GKdV model. There are severalfactors that cause the variations of the nonlinear coefficient α of the GKdV model,such as depth, stratification and background currents. In the south of South YellowSea, both the barotropic tidal currents and the baroclinic circulation are strong, and insome cases the barotropic tidal current even exceeds the phase speed of ISWs, whichmay induce an unstable condition due to the kinetic instability. The calculation ofnonlinear coefficient suggests that the internal tide will disintegrate easier during theflood case (relative to the west coast of Korea peninsula) when the propagationdirection of the barotropic tidal current is consistent with the baroclinic circulationand the calculated nonlinear coefficient is larger accordingly. In the north of SouthYellow Sea, the barotropic tidal currents and the baroclinic circulation are weaker,and the nonlinear effect is also not prominent; therefore, the disintegration will notoccur. The study of background current on the fission of ITWs may reasonablyillustrate the observational fact that ISWs are mainly observed in the south of SouthYellow Sea.Based on the previous work, a research on the parameterization of verticalturbulent mixing caused by ITWs and ISWs in the Yellow Sea is carried out. The results show that the vertical turbulent mixing mainly concentrates in the upper watercolumn (above depth about30m), and the vertical turbulent mixing caused by ISWs isnotably stronger than that by ITWs. The extreme values of the vertical turbulentviscosity coefficient υ and the vertical turbulent diffusivity coefficient κ for ISWsappear alternatively, which are mutually corresponding to the peak values of ISWs.Moreover, the Synthetic Aperture Radar (SAR) remote sensing inversion of ISWsis made by using the two-layer fluid model. Based on a criterion for the kinematicinstability of the ISWs, the breaking process of ISWs and the impact of ISWsbreaking on upwelling are analyzed in the east of Hainan Island. The amplitudes ofinternal waves are extracted from the SAR image. The results show the amplitudes ofinternal waves are consistent with the gray value in the SAR image. Both thedepression and elevation ISWs can be found in the SAR image, and their amplitudesextracted from the image are mostly according with the observation results. However,the inversion results are still a little small. The internal wave breaking mechanism inthe propagation is also discussed. A criterion for the kinematic instability of the ISWsis given. The product of the internal wave breaking caused by kinematic instability isprobably the internal swash. The internal swash will carry the cold water from thebottom of the open sea to the coast region, which may play an important role on theformation of the upwelling in the east of Hainan Island.