南海北部内潮的模态结构和非平稳性研究

Internal tides in the northern South China Sea have been examined extensively. Most previous studies suggested the dominance of the first-mode and stationary (stationary phase) internal tides in this area, but recent observations of the colleagues at home and abroad and we both found the presence of multimodal internal tides. Moreover, the internal tides were also suggested to be intermittent and non-stationary, which were different from the coherent nature of the surface tides. However, the distribution and regional differences and generation mechanisms of the multimodal structure and nonstationarity of the internal tides in the northern South China Sea remain unclear yet. Thus, based on the observational and background data from different regions, we aim to use data analysis and theoretical study and numerical simulation methods to investigate vertical modal structure and coherence of internal tides to surface tides and their nonstationarity,and reveal the difference of vertical structure and nonstationarity between the diurnal and semidiurnal components. We then study the effects of different topography and stratification structure and other background conditions on the spatial and temporal variations of the internal tides and related mechanisms, and reveal the generation mechanisms and energy transferring laws of multimodal and incoherent internal tides. Further study and understanding on the spatial structure and temporal variations of internal tides in the northern South China Sea can lay a good foundation for the study of internal wave energy transferring processes, and provide scientific basis for the development of marine resources and military security.

南海北部的内潮研究已广泛开展，以往研究大都认为该海域以第一模态和平稳性（稳定相位）的内潮为主，但近年来国内外同行和我们的观测均发现该海域的内潮存在多模态结构，且与平稳性天文潮不同而呈现间歇性和非平稳性。然而迄今为止，关于南海北部内潮多模态结构和非平稳性的分布规律、区域差异和形成机制，尚未有明确的科学认识。 本研究拟基于南海北部不同海域的观测和背景资料，采用资料分析、理论研究和数值模拟方法，研究和比较不同区域内潮的垂向模态结构，以及内潮与天文潮的相干性及非平稳性，揭示全日和半日内潮的垂向结构和非平稳性的差异；探明不同地形、水体层化等背景条件对内潮时空特性的影响机理，阐明内潮多模态结构和非平稳性的形成机制和能量传递规律。深入研究和揭示南海北部内潮的空间结构和时间演变过程，可为研究该海域的内波能量传递过程奠定良好基础，并为海洋资源开发及军事安全提供科学依据。

以往针对南海北部内潮的研究都认为该海域内潮以第一模态和平稳性能量为主，对于该海域内潮多模态结构和非平稳性信号尚未有明确科学认识。我们基于南海北部不同海域的观测和背景资料，采用资料分析、理论研究和数值模拟方法，研究和比较了内潮与天文潮的相干性及非平稳性，不同区域内潮的垂向模态结构，及其能量传递耗散规律。基于吕宋海峡2008-2009年两套长达9个月的锚系海流观测资料，给出了海盆区内潮的时空分布特性，指出了其南北不对称及复杂的时间变化规律。建立了基于ROMS的南海内潮高分辨率数值模式，刻画了吕宋海峡内潮长距离传播过程中的演化规律和能量传递过程，阐明了南海多岛礁、大陆坡和海峡等复杂地形对内潮生成、传播和耗散过程的重要影响和调制作用。进一步建立了涵盖西太及南海的内潮数值模式，研究了吕宋内潮东传在西太平洋的长距离传播演化过程。结合敏感性数值实验和理论分析，研究了地形和层结变化对内潮生成影响机制，发现高分辨率的地形和合适的背景层结是内潮模拟的关键。