Collaborative Research: Spreading, Entrainment, and Water Mass Modification in Near-Field River Plumes

智力价值：近场河流羽流的特点是超临界弗劳德数，增强混合，快速的水质量修改。这个超临界流出区域将河口与亚临界“远场”羽流分开。超临界流是由河口的地形控制引起的，并导致强烈的混合和高流速，这在沿海海洋中通常不存在。远场羽流受地球自转和局地风应力的影响较大，而超临界外流区则主要受局地平流过程和内部切变不稳定性的影响。河口流出超临界的面积只是整个河流羽流面积的一小部分，但超临界流区域内发生的盐度变化可能与河口或远场羽流内发生的盐度变化幅度相似。然而，尽管这些盐度变化的重要性，在确定水的质量特性和结构的河流羽流作为一个整体，有没有理论来描述这些转换的性质，或其依赖于不同的强迫机制。该项目的总体目标是了解和预测超临界流出区域内发生的水质量变化。这将通过观测和数值模拟技术相结合来实现。该建议的中心假设是，近场的出流特性可以预测给定的局部几何形状，在河口的流动参数，和潮汐振幅。拟议的研究的理由是，更好地了解近场羽流将扩大对河流羽流动力学的理解，并改善沿海浮力流的预测。该项目将通过追求以下两个具体目标来实现总体目标：1）与羽流的超临界流出区域内的混合和扩散有关，以及2）量化近场流出特性对河口流量特性的依赖性。预计该项目将对影响水团变化的过程，特别是近场羽流区域盐度结构的变化，产生定量的了解。这一认识将填补一个重要的空白有关河口流出大规模河流羽状流的属性。更广泛的影响：这项研究将通过更好地了解河口外流最终如何进入更广泛的尺度陆架环流，提高分析和数值研究的陆架环流。它还将增进对近场河流羽流动力学以及近场羽流在整个河流羽流背景下的作用的了解。在这方面，许多正在进行的河流羽流研究将直接受益。所提出的工作的另一个影响是使用三种不同的技术测量与近场羽流相关的湍流场的意义。点测量（微观结构）与控制体积法提供的平均值的比较将为理解湍流的不稳定性及其综合效应方面的两种测量提供重要的背景。各种技术的交叉比较也将为湍流型水下机器人这一新兴技术提供一个关键的试验环境。此外，这样一个完整的和多方面的数据集的湍流分层剪切流将是一个布恩的数值模拟寻求机会，以评估和测试新的湍流封闭技术。最后，除了撰写同行评议的科学论文外，还将编写适合工程和物理海洋学高年级本科生和研究生入门课程的互动课程材料。

Intellectual merit: A near-field river plume can be characterized by supercritical Froude numbers, enhanced mixing, and rapid water mass modification. This supercritical outflow region separates the estuary from the subcritical ' far-field' plume beyond. The supercritical flow is initiated by topographic control at the estuary mouth and results in intense mixing and high flow speeds that are typically not present in the coastal ocean. Whereas the far-field plume is influenced strongly by the earth's rotation and local wind stress, the supercritical outflow region is dominated by local advective processes and internal shear instabilities. The area over which the estuary outflow is supercritical is only a small fraction of the entire river plume area, but salinity changes occurring within the region of supercritical flow may be similar in magnitude to salinity changes that occur within the estuary or the far-field plume. However, despite the importance of these salinity changes in determining the water mass characteristics and structure of the river plume as a whole, there is no theory that describes the nature of these transformations, or their dependence on varying forcing mechanisms. The overall objective of this project is to understand and predict water mass changes that occur within the supercritical outflow region. This will be accomplished through a combination of observational and numerical modeling techniques. The central hypothesis of this proposal is that the outflow properties of the near-field may be predicted given the local geometry, flow parameters at the estuary mouth, and tidal amplitude. The rationale for the proposed research is that better understanding of the near-field plume will broaden understanding of river plume dynamics, and improve predictions of coastal buoyant flows. The project will accomplish the overall objective by pursuing the following two specific objectives: 1) Relate mixing and spreading within the supercritical outflow region of the plume, and 2) Quantify dependence of near-field outflow properties to estuarine discharge characteristics. It is expected that this project will produce a quantitative understanding of the processes affecting water mass modification, most notably changes in salinity structure, in the near-field plume region. This understanding will fill in an important gap in relating estuarine outflow to large scale river plume properties. Broader impact: This study will improve analytical and numerical studies of shelf circulation through a better understanding of how estuarine outflow ultimately enters the broader scale shelf circulation. It will also improve understanding of near-field river plume dynamics and the role of the near-field plume in the context of the river plume as a whole. In that respect, many ongoing studies of river plumes will directly benefit. Another impact of the proposed work is the significance of measuring the turbulent field associated with the near field plume using three distinct techniques. Comparison of point measurements (microstructure) with the mean values provided by a control volume method will provide important context to both types of measurements in terms of understanding the intermittency of turbulence and its integrated effects. Cross comparison of the various techniques will also provide a critical test environment for the turbulence Autonomous Underwater Vehicle, which is a new and emerging technology. Furthermore, such a complete and multifaceted data set of turbulence from a stratified shear flow will be a boon to numerical modelers seeking opportunities to evaluate and test new turbulence closure techniques. Finally, in addition to writing peer-reviewed, scientific papers, interactive course materials appropriate for upper-level undergraduate and introductory graduate classes in engineering andphysical oceanography will be developed.