Characteristics of Bolus formation from Breaking Internal Waves on Shelf Slopes

1133380 Koseff从海洋温跃层以下向岸上输送较冷、营养丰富的沃茨被认为对珊瑚礁等沿海生态系统至关重要。内孔，或团，所产生的破碎的浅水内波的斜坡上提供了一个机制，这种跨大陆架运输密集的水。事实上，观测证实，随着内波传播到浅水中，波浪变陡，这可能导致破碎，有时会产生稠密流体的湍流团，这些湍流团继续向近岸行进，与周围的地表水混合。这一机制被认为是营养盐、沉积物和幼体在深水沃茨和陆架环境之间转移的重要机制。此外，由团块驱动的迁移有可能将污染物从近海污水排放口深处迁移到近岸环境，通过捕鱼和直接接触海滩对人类健康构成风险。然而，关于内孔传播和运输的问题仍然存在，包括什么条件导致内孔的形成。因此，本计画将利用实验室实验来研究内孔的形成与物质输运过程，迄今为止，对于内孔的形成、传播与相关的物质输运的知识相当有限。因此，研究的总体目标是：（1）定量确定控制内孔从浅水内波发展的物理条件，并为此建立模型和参数化;（2）将初始流动参数与内孔的质量输送和流体夹带联系起来。 在斯坦福大学环境流体力学实验室的内波设施中进行的一系列实验室实验将研究双层系统中均匀斜坡/陆架地形上内波的变浅。 定量流动可视化技术，包括平面激光诱导荧光（PLIF）和粒子图像测速（PIV），将允许在初始流动条件，如入射波的振幅和频率的变化，对团的形成和传播的影响进行详细的研究。 额外的速度和密度场数据将量化内孔传播的质量传输，以及量化环境fluid.Overall的团夹带，该项目将有力地补充正在进行的现场研究，检查沿海生态系统中的质量传输问题。 此外，预期的结果不仅将提供洞察的物理机制变浅内波，但也将有影响的生物过程中的流体动力学和质量转移在浅水海岸系统。最后，这类研究对于解释海洋数据经常提供的“快照”，或许还能指导进一步的海洋测量，具有非常宝贵的价值。这项工作的结果将有助于研究珊瑚礁、海带森林、海草群落中的近海岸迁移和混合过程的研究人员，以及那些关注海洋排放口和其他人为排放对人类健康影响的研究人员。最后，PLIF和PIV在分层流的方法和技术，进一步发展和完善这里将使用的实验流体力学社区。

1133380KoseffThe upslope, shoreward transport of colder, nutrient-rich waters from below the ocean thermocline is thought to be critical to coastal ecosystems such as coral reefs. Internal bores, or boluses, generated by the breaking of shoaling internal waves on the slope provide a mechanism for this cross-shelf transport of dense water. Indeed, observations confirm that as internal waves propagate into shallow water, the waves steepen, which can lead to breaking and, at times, the generation of turbulent boluses of dense fluid which continue to travel inshore, mixing with ambient surface water. This mechanism is thought to be a significant mechanism for the transfer of nutrients, sediment, and larvae between deep waters and the shelf environment. Furthermore, bolus-driven transport has the potential to transport contaminants from offshore sewage outfalls at depth into the near-shore environment, posing risks for human health through fishing and direct exposure at beaches. However, questions still remain regarding internal bore propagation and transport, including what conditions cause the formation of internal bores. Thus, this project will investigate the internal bore formation and mass transport processes using laboratory experiments.To date, the knowledge of internal bore formation, propagation, and associated mass transport is fairly limited. The overall goals of the research, therefore, are to (1) quantitatively determine the physical conditions which control the development of internal bores from shoaling internal waves, and develop models and parameterizations for this, and (2) relate initial flow parameters to the mass transport and fluid entrainment of internal bores. A series of laboratory experiments in the internal wave facility of the Stanford Environmental Fluid Mechanics Laboratory will study the shoaling of internal waves on uniform slope/shelf topography in a two-layered system. Quantitative flow visualization techniques, including Planar Laser-Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV) will allow a detailed study of the effect of variations in the initial flow conditions, such as incoming wave amplitude and frequency, on bolus formation and propagation. Additional velocity and density field data will quantify the mass transport of internal bore propagation, as well as quantify the bolus entrainment of ambient fluid.Overall, the project will strongly complement ongoing field studies examining mass transfer issues in coastal ecosystems. Additionally, the expected results will not only provide insight to the physical mechanisms of shoaling internal waves, but will also have implications for biological processes affected by hydrodynamics and mass transfer in shallow coastal systems. Finally, studies such as these can be invaluable to interpreting the "snapshots" that ocean data often gives, and in perhaps directing further ocean measurements. Results from this work will be of use to researchers studying near-coastal transport and mixing processes in coral reefs, kelp forests, seagrass communities, as well as those concerned with human health impacts from ocean outfalls and other antrhopogenic discharges. Finally, the methodologies and techniques for PLIF and PIV in stratified flows that are further developed and refined here will be of use to the experimental fluid mechanics community.