长江口 M₂ 内潮生成、传播和耗散的机制研究及其季节性特征

Near estuaries, river plume can result in strong stratification in the coastal ocean; and the tide-topography interaction in the highly stratified ocean can generate active internal tides. The transport and mixing induced by the internal tide have a significant impact on the material exchange in estuarine areas. However, research on the formation and evolution mechanisms of internal tides in estuarine areas remains limited at the present. To investigate the formation and evolution mechanisms of the internal tide in estuarine areas, the spatiotemporal characteristics of the M₂ internal tide in the Changjiang (Yangtze) River estuary and its adjacent seas were intensively examined using a high-resolution numerical model. The results show that the barotropic tidal forcing is particularly significant in the areas including the 20-m isobath, around islands, and in submerged shelf valleys. The conversion rate from barotropic to baroclinic energy is high, resulting in strong baroclinic kinetic energy. Energy budget analysis reveals that the M₂ internal tide kinetic energy propagates mainly outward from nearshore regions, and dissipated significantly when energy encounters abrupt topographic features such as the 20-m isobath or areas around islands. Additionally, the M₂ internal tide exhibits significant seasonal variations. In general, the baroclinic kinetic energy is the highest in summer, stronger near the Zhoushan Archipelago in autumn, and becomes very weak in winter. The seasonal variations are closely related to the seasonal stratification in the estuary area. The spatiotemporal variation of internal tides in the estuary plays a crucial role in the transport of materials and mixing in local area. The research findings can provide a theoretical basis for understanding the ecological, sedimentary, and other processes in this area.