地转条件下理想河口羽流的演变与输运及其层化湍流、卷吸和混合机制

河口羽流是连接陆地与海洋的纽带，其动力机制对了解近海动力过程及生态环境保护十分重要。通常认为河流冲淡水在科氏力和密度差的作用下形成河口涡旋并沿岸输运，但由于其他外力的存在，其动力过程变得复杂。目前，国内外的研究主要侧重于针对特定环境下的单一河口，对河口羽流的普适理论还亟待完善。本项目拟通过实验室转台模拟理想河口羽流，结合粒子成像技术和平面激光诱导荧光技术采集瞬时准三维速度和密度场，深入剖析滞留时间、湍混合通量和冲淡水输运对地转频率、河流流量、层化结构、潮汐和背景流的响应机制，并结合高分辨率水动力模型扩展实验参数，建立理论模型。在此基础上，本项目拟采集长江口羽流的现场观测数据以进一步验证理论模型。项目研究成果将全面揭示河口羽流在不同外界因素下的演变过程，完善淡盐水间的层化湍流混合机制，同时丰富对长江口羽流及浙闽海岸冲淡水输运的研究，对进一步认识、开发和保护海洋具有重要意义。

River plumes play a critical role in the exchange of materials between the land and the ocean and their dynamic mechanisms are important in understanding coastal dynamic processes and ecosystem protection. When buoyant fluid is released near a vertical wall in a rotating system, Coriolis force guides the density-driven flow along the wall, creating an anticyclonic bulge (in the Northern Hemisphere) near the river mouth. However, the real river plume system is much more complex. Dynamics of individual river plume system have been studied thoroughly over past decades, but the fundamental mechanism is still lack of investigations. In this proposed study, we will simulate an idealized river plume system on a rotating table and obtain velocity and density fields by using the combined Particle Image Velocimetry and Planar Laser Induced Fluorescence (PIV-PLIF) technology. The study will investigate the responding mechanisms of plume residence time, turbulent mixing flux and freshwater transport under different external forces (e.g. earth rotation, river discharge, density differences, tides and ambient flows). The theoretical model will be constructed by combining results of laboratory experiments and high-resolution numerical simulations, and then validated using in-situ observations at real river plume systems such as the Changjiang River Plume. This project will reveal the evolution of river plume systems under different external forces, and associated stratified-shear turbulence, entrainment and mixing. The fate of the Changjiang diluted water and its impact on Zhe-Min coastal regions will also be discussed based on the theoretical and observational studies. Overall, the study will enhance our understanding in coastal dynamics, contributing to the exploitation and protection of the marine ecosystem.