Propagation Speeds of Shoaling Internal Solitary Waves in the South China Sea: A satellite Investigation and Theoretical Interpretation

Internal tides generated over the ridges in the Luzon Strait are the source of internal solitary waves (ISWs) in the South China Sea (SCS). The present study focuses on the incoming ISW east of Dongsha atoll, where ISWs shoal onto the continental slope. The propagation speeds of the ISWs were estimated by the time evolution of the surface manifestation of ISW characterized by the sunlight reflectance pattern of the true color imagery taken by the Himawari geostationary weather satellite. The results were verified by a mooring array off east of the atoll. The nearly consecutive snapshots captured every 10 mins reveal that the propagation speeds of ISWs have strong dependence on the local depth, decreasing at a hyperbolic tangent function with depth decreases. As the ISWs move westward across ~700-m depth, the reflection waves generally appear and move eastward, but they can decay fast. Further, linear, weak nonlinear, and fully nonlinear wave theories are employed to examine the satellite observations.