EVOLUTION OF NONLINEAR INTERNAL WAVES IN THE EAST AND SOUTH CHINA SEAS

Synthetic Aperture Radar (SAR) images from ERS-1 have been used to stu dy the characteristics of internal waves northeast and south of Taiwan in the East China Sea, and east of Hainan Island in the South China S ea. Rank-ordered packets of internal solitons propagating shoreward fr om the edge of the continental shelf were observed in the SAR images. On the basis of the assumption of a semidiurnal tidal origin, the wave speed can be estimated and is consistent with the internal wave theor y. By using the SAR images and hydrographic data, internal waves of el evation have been identified in shallow water by a thicker mixed layer as compared with the bottom layer on the continental shelf. The gener ation mechanism includes the influences of the tide and the Kuroshio i ntrusion across the continental shelf for the formations of elevation internal waves. The effects of water depth on the evolution of soliton s and wave packets are modeled by the nonlinear Kortweg-deVries (KdV) type equation and linked to satellite image observations. The numerica l calculations of internal wave evolution on the continental shelf hav e been performed and compared with the SAR observations. For a case of depression waves in deep water, the solitons first disintegrate into dispersive wave trains and then evolve to a packet of elevation waves in the shallow water area after they pass through a ''turning point'' of approximately equal layer depths that has been observed in the SAR image and simulated by the numerical model. The importance of the diss ipation effect in the coastal area is also discussed and demonstrated.