Collaborative Research: Creation of a coastal current - The transition of an energetic river discharge from buoyant jet to geostrophic plume

合作研究：沿海流的产生——充满活力的河流排放从浮力射流到地转羽流的转变

• 批准号: 0850622
• 负责人: Robert Hetland
• 金额: $ 30.83万
• 依托单位: Texas A&M Research Foundation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-03-15 至 2014-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0850622&HistoricalAwards=false
• 关键词: Collaborative; Research; Creation; coastal; current

The mid-field river plume is a transition area where a multitude of geophysical mechanisms act to constrain and transform a strongly inertial jet into a geostrophic coastal current. The near-field jet is the area over which the estuarine outflow is supercritical, where advection and shear mixing dominate the dynamics, where the shape of the estuary mouth is important in determining the shape of the near-field plume flow structure, and where the flow is often directed offshore. This is distinct from the geostrophic far-field river plume where the earth?s rotation, wind, and background flow dominate the evolution of the plume, and the flow is primarily along-shore. Although entrainment of ambient water is high in the near-field, the far-field plume tends to form a coastally-trapped boundary current where entrainment is quite small in the absence of other forcing mechanisms such as winds and tides. Within the mid-field, plume spreading must be arrested, mixing reduced, and the flow directed along-shore. Rotation or background currents may arrest plume spreading, preventing plume acceleration and reducing further mixing in the plume. Frontal processes enhance mixing locally, but have an unknown effect on the core of the plume. The contribution of each of these processes to the spreading and mixing of the plume is expected to depend strongly on the scale of the plume. A quantitative understanding of the relative role of these processes is necessary for determining the dynamical role of river plumes of different scales on shelf circulation and transport.The overall objective of this proposal is to better understand how small scale processes of O(1 km) operating near an estuary mouth transition to larger-scale (O(100 km)) buoyancy driven coastal currents through the intermediate scales of O(10 km). The central hypothesis is that a suite of processes operating in the mid-field plume modify the plume spreading and mixing and thus the transition between the near- and far-field plumes. The proposed work will establish the relative influence of a number of key mechanisms in setting the spatial and temporal scales of the near- and mid-field plume regions. It will constrain the total water mass modification in the initial evolution of the plume and help understand how continental shelf-scale coastal currents are formed. The following three specific objectives will be pursued:1) Quantify the processes that arrest plume spreading,2) Relate reduced mixing rates to arrested plume spreading and3) Determine net mixing in the near- and mid-field regions.The approach will be one that integrates field observations, laboratory experiments and numerical model experiments. Such an approach is necessary to accurately describe and quantify the full array of physical processes that contribute to mixing in natural plumes and to determine how these processes are modified across a broad parameter space. Detailed field measurements in the Merrimack River plume will be complimented with non-rotating and rotating laboratory experiments and laboratory and geophysical scale numerical model experiments. This work will fill an important gap in the ability to relate fresh water discharge to large scale coastal ocean circulation.The broader impacts of the study are two-fold: better understanding the role of river plumes in coastal oceanography, and education of graduate and undergraduate students. The study will determine how river inflows affect water properties over a large area influenced by plumes and provide better predictive capability to coastal managers. It will fund three graduate students, one at each of the three participating institutions. In addition, the field campaigns will provide a unique learning experience not only for the three funded graduate students, but for additional graduate and undergraduate students. The use of a number of small vessels for synoptic research will require graduate students to assume chief scientist responsibilities on individual vessels, providing a level of autonomy and responsibility rare for larger scale physical oceanographic field programs.

中场河羽是一个过渡区域，其中多种地球物理机制将强烈的惯性射流限制为地球形沿海电流。近场射流是河口流出的区域超临界的区域，对流和剪切混合占主导地位，其中河口嘴的形状对于确定近场羽流量结构的形状以及流动通常定向在海上近海很重要。这与地球远场河羽不同，地球的旋转，风和背景流占据了羽流的演变，并且流动主要沿陆上沿岸。尽管近场环境水的夹带很高，但远场羽流倾向于形成沿海捕获的边界电流，在没有其他强迫机制（例如风和潮汐）的情况下，夹带很小。在中场内，必须逮捕羽流散开，混合减少，并沿近岸进行流动。旋转或背景电流可能会阻止羽流的扩散，防止羽状加速并减少羽流中的进一步混合。额叶过程可在本地增强混合，但对羽流的核心具有未知的影响。这些过程中的每一个对羽流的扩散和混合的贡献预计将在很大程度上取决于羽流的规模。对这些过程的相对作用的定量理解对于确定不同尺度循环和运输中不同尺度的河流的动态作用是必要的。该提议的总体目标是更好地了解O（1 km）在河口的小尺度过程中如何在河口的口腔过渡到较大尺度（O（100 km））buoy buoyand buoyand buoyance drived Coastal drived coastal drived coastal drived cartional drive coaster drived cartive cartional diethriped s ratiessipersipersipersipersipersipersipersiped s s s s s o（10 KM）。中心假设是，在中场羽流中运行的一系列过程会修改羽流的扩散和混合，从而改变了近场和远场羽流之间的过渡。拟议的工作将确定许多关键机制在设置近场和中场羽状区域的空间和时间尺度方面的相对影响。它将限制羽流的初始演变中的总水量修饰，并有助于了解大陆架规模尺度沿海电流的形成方式。将实现以下三个特定目标：1）量化停滞羽流传播的过程，2）将降低的混合速率与逮捕的羽流传播和3）确定在近场和中场区域中确定净混合。该方法将是整合现场观测值，实验室实验，实验实验和数字模型实验的方法。这种方法是必要的，以准确描述和量化有助于自然羽流中混合的全部物理过程，并确定如何在广泛的参数空间中修改这些过程。 Merrimack河羽流中的详细现场测量将与非旋转和旋转的实验室实验以及实验室以及地球物理规模的数值模型实验相称。这项工作将填补将淡水排放到大规模沿海海洋循环的能力的重要空白。该研究的更广泛影响是两倍：更好地了解河流在沿海海洋学中的作用，以及对研究生和本科生的教育。该研究将决定河流流入如何影响受羽毛影响的大面积的水性质，并为沿海经理提供更好的预测能力。它将为三个参与机构中的三个研究生提供资金。此外，现场活动不仅将为三位资助的研究生提供独特的学习经验，而且还将为其他研究生和本科生提供。使用许多小型船只进行天气研究将要求研究生承担单个船只的首席科学家责任，从而为大规模的物理海洋学野外计划提供一定程度的自治和责任。