Oceanic Rossby waves play a crucial role in shaping the physical and biological dynamics of both open and coastal oceans, especially within the tropical band spanning between the 10°S and 10°N parallels. Yet, the extent to which Rossby waves can transmit and impact the hydrography and ecosystem of semi-enclosed seas like the South China Sea (SCS) remains unclear. This study aims to investigate the transmission of Rossby waves through the Philippine archipelago, using satellite altimeter-derived sea level anomaly (SLA) and coastal tide gauge records. Our findings reveal that westward-propagating Rossby waves in the tropical Pacific Ocean with a wave speed of ~0.64 m s−1 first entered the Celebes Sea, and then passed through the Sibutu Passage into the Sulu Sea from April to December 2017. Subsequently, the waves propagated along the northeast coast of Sabah and the east coast of Palawan before exiting through the Mindoro Strait to the central SCS. Additionally, a β-refracted Rossby wave with wave speed of 0.28 m s−1 also penetrated the archipelago but at a latitude further north ~10°N from July to November via Surigao Strait and propagated toward the south and north of Palawan, ultimately reaching the west coast of Palawan in the eastern central SCS. This study verifies that the transmission of Rossby waves originating from the east of the Philippines could induce intraseasonal sea level oscillations off Palawan, which could subsequently propagate westward across the central SCS as identified in previous field observations.

Measurements in the South China Sea reveal the structure of the bottom boundary layer beneath onshore propagating highly nonlinear internal solitary waves of depression. Offshore directed free stream velocities beneath thirteen waves with durations of 10-20 minutes and velocities up to 1.4 m/s are consistent with the solitary wave solution to the Korteweg de Vries equation, as are phase velocities estimated from pressures and free stream velocities. The measurements indicate a thin layer during free stream acceleration, a thicker layer with an inflected velocity during deceleration, and a long lived sediment laden wake, after wave passage in the free stream, with velocities opposite those at maximum flow strength. Reynolds averaged Navier Stokes simulations with the k-ε turbulence model reproduce the measured velocities and turbulent Reynolds shear stresses accurately during acceleration and early deceleration. However, differences between the simulations and the measurements during late deceleration and in the wake suggest energetic large scale turbulence not represented by the simulations. This turbulence might be similar in origin to coherent vortices that have been observed in laboratory experiments and direct numerical simulations at much smaller Reynolds numbers, which have been attributed to absolute and global instabilities resulting from inflected velocity profiles.