Numerical Study On The Generation And Propagation Of Internal Tides In The Luzon Strait

Internal tides are internal gravity waves with tidal frequencies, they play a significant role in energy distribution and mixing. Connecting both the Western Pacific and South China Sea,Luzon Strait is one of the most energetic areas generating internal tides. Observational evidence show that internal tides radiate from Luzon Strait and propagate thousands of kilometers. In this paper ROMS(Regional Ocean Model System) is used to simulate internal tides in the Luzon Strait, we employ three-dimensional numerical simulations with real bathymetry and perform detailed analyses of internal tides energetics and dynamics to understand how they are generated in the Luzon Strait and how they propagate in the Western Pacific and South China Sea. The simulated results indicate that:1. Three-dimensional high-resolution internal tides field of both Western Pacific and South China Sea was reproduced. In the Luzon Strait17.3 GW(12.3 GW) of M2(K1) barotropic energy is converted to baroclinic part. Among which 39% of the converted baroclinic energy dissipate locally, and the rest of it radiate into both South China Sea andWestern Pacific. For M2(K1) internal tides, 5.6 GW(3.8 GW) of baroclinic energy radiated into South China Sea, and 5.0 GW(3.7 GW)radiated into Western Pacific.2. Low-mode diurnal and semidiurnal internal tides generated at Luzon Strait can propagate a long distance from generation site, but they shows different pattern and variation during propagation. Both diurnal and semidiurnal internal tides can propagate through the South China Sea arriving at the coast of Vietnam. M2 internal tides from Luzon Strait radiate into the South China Sea into two beams and perform north-south asymmetry pattern, the intensity of north beam(4.1 GW) is about twice the south one(1.9 GW). M2(K1) internal tides originating in the Luzon Strait can propagate over 1500(2000) km in the Western Pacific. Diurnal internal tides with lower frequency are more affected by the earth’s rotation. For M2 internal tides the propagation direction remains nearly unchanged, but diurnal internal tides(K1 and O1) bend toward the Equator during propagation. K1 internal tides are found to maintain a better strength than M2 internal tides during long-range propagation.3. A great deal of energy radiate from the generation sites to far-field due to internal tides propagation, resulting in a broad spacial distribution of dissipation. Luzon Strait and regions around Dongsha Island are important sinks for baroclinic energy in the South China Sea. In the Western Pacific K1 internal tides lose more energy in low latitudes, thepossible reasons may be that K1 internal tides bend toward the Equator during propagation. The diapycnal mixing around generation sites and far-field are enhanced due to tidal mixing. The diapycnal mixing elevation induced by M2 internal tides is stronger than K1 internal tides,especially in the regions between Luzon Strait and the continental shelf.