Characteristics of Bolus formation from Breaking Internal Waves on Shelf Slopes

1133380科斯夫从海洋温跃层下面向上、向岸上输送较冷、营养丰富的水域被认为对珊瑚礁等沿海生态系统至关重要。斜坡上浅海内波的破裂所产生的内孔，或称内丸，为这种密集水的跨陆架运输提供了一种机制。事实上，观察证实，当内波传播到浅水中时，波变陡，这可能导致破裂，有时还会产生稠密流体的湍流团，这些流体继续向近岸流动，与周围的地表水混合。这一机制被认为是营养物质、沉积物和幼虫在深水和陆架环境之间转移的重要机制。此外，由推进剂驱动的运输有可能将污染物从近海排污口深处输送到近岸环境，通过捕鱼和直接暴露在海滩上对人类健康构成风险。然而，关于内孔的传播和运输，包括什么条件导致内孔的形成，仍然存在问题。因此，这个项目将通过实验室实验来研究内孔的形成和质量传输过程。到目前为止，关于内孔的形成、传播和相关的质量传输的知识相当有限。因此，这项研究的总体目标是(1)定量确定控制浅滩内波形成内孔的物理条件，并为此开发模型和参数；(2)将初始流动参数与内孔的质量传输和流体夹带联系起来。斯坦福环境流体力学实验室内波装置的一系列实验室实验将研究两层系统中内波在均匀斜坡/陆架地形上的浅化。定量流动显示技术，包括平面激光诱导荧光(PLIF)和粒子图像测速(PIV)，将允许详细研究初始流动条件的变化，如入射波的幅度和频率，对团团形成和传播的影响。额外的速度和密度场数据将量化内孔传播的质量传输，以及环境流体的推进剂夹带。总体而言，该项目将有力地补充正在进行的考察沿海生态系统中质量传输问题的实地研究。此外，预期结果不仅将提供对浅海内波的物理机制的洞察，而且还将对浅海沿岸系统中受水动力和质量转移影响的生物过程产生影响。最后，这样的研究对于解释海洋数据经常给出的“快照”，以及可能指导进一步的海洋测量，可能是非常有价值的。这项工作的结果将有助于研究珊瑚礁、海藻森林、海草群落中近岸迁移和混合过程的研究人员，以及那些关注海洋排污口和其他反生物排放对人类健康影响的研究人员。最后，本文进一步发展和完善的层状流中PLIF和PIV的方法和技术将对实验流体力学领域有所帮助。

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.