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<p>Internal tides serve as an important carrier for the transfer, propagation, and dissipation of barotropic tidal energy in the South China Sea (SCS), and their variability is strongly modulated by multi-scale dynamic processes. Using the Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM), we developed a high-resolution three-dimensional circulation model for simulating temperature, salinity, and currents in the SCS from January 2021 to January 2022. Through barotropic/baroclinic separation, harmonic analysis, and vertical mode decomposition, we systematically investigated the seasonal and spatial variability of incoherent diurnal internal tides (ICIT), and explored their underlying generation and modulation mechanisms. The results reveal pronounced seasonal variability in diurnal internal tide energy, with higher energy levels in winter/summer, and weaker in spring/autumn. The Luzon Strait, Dongsha Islands, the southern coast of Hainan Island, and the southwestern waters of the Nansha Islands are identified as the major high-energy regions for diurnal internal tides. In contrast, ICIT dominate over the northwestern continental slope, eastern Hainan waters, and the southwestern basin. ICIT are primarily modulated by multi-scale dynamic forcings, including monsoons, typhoons, and local upwelling. Results from the vertical mode decomposition indicate distinct seasonal differences in modal energy partitioning. The first mode dominates in autumn, accompanied by substantially enhanced higher-mode contributions, whereas the second mode predominates in winter (68.96 J/m<sup>3</sup>, 51.2% of the total kinetic energy). Correlation analysis further demonstrates that ICIT are promoted by mesoscale eddies and vertical mixing but are significantly suppressed by stratification. Furthermore, intensified wind stress is found to enhance ICIT. These findings enhance understanding of ICIT in the SCS and provide critical insights for regional ocean mixing parameterization, climate model optimization, and deep-sea environment assessments.</p>

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Seasonal-spatial variability of incoherent diurnal internal tides and their multi-scale controls in the South China Sea

  • 期刊论文

  • 发表日期：

    2026年7月31日

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  • Shuo Li,
  • Jingui Liu,
  • Zhenhui Yi,
  • Wenjing Zhang,
  • Jiawei Zhang,
  • Tianyu Zhang,
  • Shunqi Pan

摘要

Internal tides serve as an important carrier for the transfer, propagation, and dissipation of barotropic tidal energy in the South China Sea (SCS), and their variability is strongly modulated by multi-scale dynamic processes. Using the Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM), we developed a high-resolution three-dimensional circulation model for simulating temperature, salinity, and currents in the SCS from January 2021 to January 2022. Through barotropic/baroclinic separation, harmonic analysis, and vertical mode decomposition, we systematically investigated the seasonal and spatial variability of incoherent diurnal internal tides (ICIT), and explored their underlying generation and modulation mechanisms. The results reveal pronounced seasonal variability in diurnal internal tide energy, with higher energy levels in winter/summer, and weaker in spring/autumn. The Luzon Strait, Dongsha Islands, the southern coast of Hainan Island, and the southwestern waters of the Nansha Islands are identified as the major high-energy regions for diurnal internal tides. In contrast, ICIT dominate over the northwestern continental slope, eastern Hainan waters, and the southwestern basin. ICIT are primarily modulated by multi-scale dynamic forcings, including monsoons, typhoons, and local upwelling. Results from the vertical mode decomposition indicate distinct seasonal differences in modal energy partitioning. The first mode dominates in autumn, accompanied by substantially enhanced higher-mode contributions, whereas the second mode predominates in winter (68.96 J/m3, 51.2% of the total kinetic energy). Correlation analysis further demonstrates that ICIT are promoted by mesoscale eddies and vertical mixing but are significantly suppressed by stratification. Furthermore, intensified wind stress is found to enhance ICIT. These findings enhance understanding of ICIT in the SCS and provide critical insights for regional ocean mixing parameterization, climate model optimization, and deep-sea environment assessments.