Southward Internal Tides in the Northeastern South China Sea

The M-2 internal tides in the northeastern South China Sea are studied using satellite altimeter data from 1992-2018. By an improved mapping technique that combines plane wave analysis and two-dimensional spatial filtering, multiple internal tides are separately extracted with weak internal tides becoming detectable. The satellite results reveal for the first time a 300-km-long southward M-2 internal tidal beam in the northeastern South China Sea. The generation source is on the steep continental slope at the southern entrance to the Taiwan Strait. It ranges from 118-120 degrees E along 22 degrees N. Combining satellite-observed internal solitary waves and internal tides, it is found that the onshore radiation evolves into nonlinear solitary waves and the offshore radiation in the form of linear internal tides. Based on the 26-year-coherent satellite results, the integrated southward energy flux is 0.18 GW, about 10% of the westward energy flux from the Luzon Strait. In the northeastern South China Sea, the westward and southward internal tides form a multiwave interference field, which features significant spatial variations in the magnitude and direction of energy flux. Further analyses reveal that the steep continental slope radiates southward semidiurnal M-2 and S-2 internal tides, but not diurnal K-1 and O-1 internal tides.