[A-OS12] Ocean Science Revealed by Global Observation System

[AOS12-09] Predicting Internal Solitary Wave Propagation and Arrival Time in the Northern South China Sea: Insights from Internal Tide Model, Satellite Images, and Field Observations

*Chia-Hsuan Chien¹, Ming-Huei Chang^1,2, Yu-Yu Yeh¹ (1.Institute of Oceanography, NTU, 2.Ocean Center, National Taiwan University)

Keywords:South China Sea, internal tides, internal solitary waves, nonlinear effects, internal waves forecast model

Internal Solitary Waves (ISWs) are ubiquitous in the coastal marginal seas of the world’s oceans, playing a crucial role in shaping marine environments and ecosystems. The northern South China Sea (SCS) has garnered particular attention, as ISWs exhibit horizontal and vertical velocities reaching 2 m s^-1 and 0.5 m s^-1, respectively, with an amplitude of 100-200 m. Therefore, it is crucial to predict their propagation and arrival time. ISWs evolve from the nonlinear dispersion of internal tides generated by the interaction between barotropic tidal flows and two north-south-oriented ridges of the Luzon Strait. The mechanism sheds light on their predictability using an internal tide prediction model. Here, the internal tide-induced sea surface height (ITSSH) predicted from the Multivariate Inversion of Ocean Surface Topography, Internal Tide Model (MIOST-IT) is used to relate with the ISWs detected by the mooring and shipboard measurements and Himawari-8 (H8) satellite images. MIOST-IT indicates that internal tides are primarily generated in the eastern ridge by diurnal tides and in the western ridge by semidiurnal tides, propagating westward toward the Dongsha Atoll. By comparing with the observations and H8 images, it is encouraging to reveal that ISW events are primarily located near the transition points where the ITSSH transits from a negative to a positive value, with an uncertainty of ~3 hours. This suggests that ISWs are located at the crest of the internal tides, as the isopycnal displacement of an internal tide typically leads its surface counterpart by a phase of π/2. This is plausible because ISWs have an additional nonlinear wave speed compared to their parent internal tides. Once the depressed ISWs are initially formed in the trough of the internal tide, the nonlinear wave speed causes the ISWs to propagate toward the wave crest of the internal tides. We estimate the nonlinear wave speed to be between 0.2 and 0.7 m s^-1, suggesting that the occurrence of nonlinear dispersion lies between 118.6 °E and 122 °E. Further studies are needed.