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

合作研究：近场河流羽流的扩散、夹带和水团改变

• 批准号: 0550096
• 负责人: Daniel MacDonald
• 金额: $ 34.52万
• 依托单位: University of Massachusetts, Dartmouth
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-03-01 至 2010-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0550096&HistoricalAwards=false
• 关键词: Collaborative; Research; Spreading; Entrainment; Water

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.

智能优点：近场河流羽流的特征是超临界弗劳德数、增强的混合和快速的水团修改。这一超临界流出区将河口与其外的亚临界“远场”羽流分开。超临界水流是由河口地形控制引发的，并导致强烈的混合和高流速，这在沿海海洋中通常是不存在的。远场羽流受地球自转和局地风应力的影响较大，而超临界流出区主要受局地平流过程和内部切变不稳定的影响。河口出流超临界区域只占整个河流羽流面积的一小部分，但在超临界流区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在大小上相似。然而，尽管这些盐度变化在决定整个河流羽流的水团特征和结构方面很重要，但没有理论来描述这些变化的性质，或它们对不同强迫机制的依赖。该项目的总体目标是了解和预测超临界流出区内发生的水团变化。这将通过观测和数值模拟技术的结合来实现。这一建议的中心假设是，近场的外流特性可以在给定局部几何形状、河口水流参数和潮汐振幅的情况下预测。拟议研究的理由是，更好地了解近场羽流将扩大对河流羽流动力学的理解，并改进对沿海浮力流动的预测。该项目将通过追求以下两个具体目标来实现总体目标：1)将羽流超临界流出区内的混合和扩散联系起来；2)量化近场流出特性对河口流量特性的依赖关系。预计该项目将对影响近场烟羽区域水团变化的过程有一个定量的了解，尤其是盐度结构的变化。这一认识将填补将河口外流与大尺度河流羽流特性联系起来的一个重要空白。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大范围的陆架循环，来改进对陆架循环的分析和数值研究。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中的作用的理解。在这方面，许多正在进行的河流羽流研究将直接受益。这项拟议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。将点测量(微观结构)与控制体积法提供的平均值进行比较，将为了解湍流的间歇性及其综合影响这两种类型的测量提供重要的背景。各种技术的交叉比较也将为湍流自主水下机器人这一新兴技术提供一个关键的测试环境。此外，这种来自分层剪切流的完整和多方面的湍流数据集将对寻求评估和测试新的湍流闭合技术的数值建模人员来说是一个福音。最后，除了撰写同行评议的科学论文外，还将编写适用于工程和物理海洋学的本科生和研究生入门班的互动式课程材料。