The M₂ 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 M₂ 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^oE along 22^oN. 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 M₂ and S₂ internal tides, but not diurnal K₁ and O₁ internal tides.

南海东北部的南向内潮

中文摘要：利用1992-2018年卫星高度计数据研究了南海东北部M₂内潮。借助平面波分析与二维空间滤波相结合的改进映射技术，可以将多个内潮分离并提取，还能检测微弱的内潮。卫星观测结果首次在南海东北部发现了一条长度为300 km的南向M2内潮束。其生成源是位于台湾海峡南部入口的陡峭的大陆坡，范围为22^oN的118-120^oE。结合卫星观测的内孤立波和内潮，发现向岸辐射演变为非线性孤立波，离岸辐射演变为线性内潮。基于26年连续的卫星观测结果显示南向能量通量为0.18 GW，约为吕宋海峡西向能量通量的10%。西向和南向的内潮在南海东北部形成多波干扰场，其能量通量的量级和方向存在显著的空间变化。进一步分析表明陡峭的大陆坡向南辐射的是半日内潮M₂和S₂，而不是K₁和O₁日内潮。