Dynamics of a Rotating, Supercritical Large-River Plume

这个项目分析了从哥伦比亚河河口出现的超临界旋转羽流的动力学。由美国国家科学基金会资助的河流影响陆架生态系统（RISE）项目为世界上大型河流的羽流生态系统动力学提供了一个新的视角。羽流的功能在很大程度上取决于小尺度过程的联系，如50米宽的非静水俯冲和羽流产生的非线性内波（NLIW），到更大尺度，如10-30公里宽的潮汐羽流。该项目结合了分析和数值模型、遥感和船舶数据，以解决多个尺度上的问题，并以传统模型无法完成的方式进行跨尺度整合。本文将研究以下问题：1)潮汐羽流的动力学和能量学是什么，以及观测到的南北不对称性如何影响羽流的能量学？朗朗日锋面方程提供了一个关于羽流径向扩散动力学的优雅公式，但实际的羽流在其南侧更深、更慢。这种不对称影响锋面能量学，主要是由于羽流与底层潮汐涡度场的相互作用。非对称性导致NLIW的产生始于羽流的南侧，并顺时针推进。该项目扩展了现有的径向对称、解析和数值锋面模型，以描述实际羽流结构的动力学和能量学。使用现有数据验证模型。2)是什么控制了NLIW的生成，这一生成与特定的额叶结构和动力学有何关系？当潮柱锋衰减到亚临界状态时能否产生NLIW取决于潮柱锋的相对深度和潮柱锋衰减到的旋转羽流状态。基于羽流锋面、羽流近场和NLIW能量学，定义了NLIW的生成准则，从而可以用解析模型和数值模型来预测NLIW的生成。3)如何模拟具有突出的俯冲和再循环特征的实际羽流锋的结构和动力学？现有的拉格朗日额叶理论没有描述实际的额叶结构？与水力控制理论一样，它预测了过渡的位置和性质，而不确定其结构，尽管垂直混合的能量损失是该理论的一部分。遥感和船舶数据激励和指导了新模型的发展，这些模型包含了非流体静力的羽前俯冲。4)潮羽是如何融入近场的？潮羽和近场是如何混入周围水域的？何时何地从下方向羽流输入养分？CR是贫营养的，但羽流是高产的。大多数羽流混合到周围水域，几乎所有从下面输入的营养物质都发生在潮汐羽流和近场。混合机制包括锋面过程、羽流上升、风和nliw -平均切变相互作用。本项目利用精细结构和水团分析、SAR数据和波浪理论分析羽流混合的位置、时间和机制。总之，这个项目解释了潮汐羽流的小尺度过程如何影响由区域模式再现的大尺度过程。因此，它为河流羽流的关键要素如何工作提供了一个更好的图像，并且迫切需要为浮力羽流的建模提供指导。浮力羽流在许多情况下都很重要，大河及其羽流在全球碳、养分和沉积物收支中起着重要作用。RISE的研究表明，哥伦比亚烟柱是大河烟柱的一个可处理的例子，烟柱与上升流的生态系统相互作用，在某种程度上促进了沿海的生产。此外，人类和气候驱动的季节性流动变化正在改变羽流与海岸过程的相互作用，可能会影响陆地碳和营养物质的命运。羽流和底层水之间的大部分相互作用发生在潮汐羽流中，这是一种新定义的结构，但仍未完全被理解，以及它所融合的羽流近场。此外，幼鲑鱼（包括那些濒临灭绝的鱼类）在潮汐羽流及其前缘广泛觅食。因此，本项目进行的分析既有助于了解具有全球意义的进程，又有助于区域管理工作

This project analyzes the dynamics of the supercritical, rotating plume emerging from the mouth of the Columbia River. The River Influenced Shelf Ecosystems (RISE) project, funded by NSF, provides a new view of plume ecosystem dynamics for the world's large rivers. The functioning of the plume depends vitally on the linkage of small-scale processes, like the 50m-wide non-hydro-static plunge and plume-generated non-linear internal waves (NLIW), to larger scales, e.g., the 10-30km wide tidal plume. This project combines analytical and numerical models, remote sensing, and vessel data to address questions on multiple scales and to integrate across scales in a manner that cannot be accomplished using conventional models. The following questions will be investigated: 1) What are the dynamics and energetics of the tidal plume, and how does the observed north-south asymmetry of the plume front influence plume energetics? Langrangian frontal equations provide an elegant formulation of the dynamics of a radially spreading plume, but the actual plume is somewhat deeper and slower on its south side. This asymmetry influences frontal energetics and occurs primarily because of an interaction of the plume with the underlying tidal vorticity field. Asymmetry causes NLIW generation to begin on the south side of the plume and progress clockwise. This project extends existing radially symmetric, analytical and numerical frontal models to describe the dynamics and energetics of the actual plume configuration. Models are verified using existing data. 2) What controls NLIW generation, and how can this generation be related to specific frontal structures and dynamics? Whether NLIW can be generated as the tidal plume front decays to a subcritical state depends on the relative depths of the plume front and rotating plume state to which the front decays. A generation criterion, based on plume front, plume near-field and NLIW energetics, is defined so that the generation of NLIW can be predicted with analytical and numerical models. 3) How can the structure and dynamics of the actual plume front be modeled, with its prominent plunge and recirculation? Existing Lagrangian frontal theory does not describe actual frontal structure ? like hydraulic control theory, it predicts the location and properties of a transition without determining its structure, even though energy loss to vertical mixing is part of the theory. Remote sensing and vessel data motivate and guide development of new models that incorporates the non-hydrostatic plume-front plunge. 4) How does the tidal plume blend into the near-field? How do the tidal plume and near-field mix into ambient waters? When and where does nutrient input to the plume from below occur? The CR is oligotrophic, but the plume is highly productive. Most plume mixing into ambient waters and almost all nutrient input from below occurs in the tidal plume and near-field. Mixing mechanisms include frontal processes, plume lift-off, winds, and NLIW-mean shear interaction. This project uses fine-structure and water mass analyses, SAR data, and wave theory to analyze the location, timing and mechanisms of plume mixing. In summary, this project explains how the small-scale processes of the tidal plume influence larger scale processes that are reproduced by regional models. Thus, it provides a much improved picture of how key elements of a river plume work and urgently needed guidance for modeling of buoyant plumes. Buoyant plumes are important in many contexts, and large rivers and their plumes play a major role in the global carbon, nutrient and sediment budgets. RISE has shown that the Columbia plume is a tractable example of a large-river plume, and that the plume interacts with the upwelling eco-system in a way that enhances coastal production. Human and climate-driven changes in flow seasonality are, moreover, altering the interaction of the plume with coastal processes, likely affecting the fate of carbon and nutrients from land. Much of the interaction between the plume and underlying waters takes place in the tidal plume, a newly defined structure that remains incompletely understood, and the plume-near-field into which it merges. Moreover, juvenile salmonids (including those of endangered stocks) feed extensively in the tidal plume and at its fronts. Thus, the analyses carried out by this project both facilitate understanding of processes with global significance and contribute to regional management efforts