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

中场的河流羽流是一个过渡区，在那里的许多地球物理机制的作用，以限制和转换成地转沿岸流的强烈惯性射流。近场急流是河口流出超临界的区域，其中平流和剪切混合占主导地位的动力学，河口的形状在确定近场羽流结构的形状方面很重要，并且流通常指向离岸。这是不同于地转远场河流羽流的地球在哪里？的旋转，风，和背景流主导的烟羽的演变，和流动主要是沿海岸。虽然夹带的环境水是高的近场，远场羽流往往会形成一个沿海捕获的边界电流夹带是相当小的其他强迫机制，如风和潮汐的情况下。在中场内，必须阻止羽流扩散，减少混合，并使气流沿海岸流动。旋转或背景流可阻止羽流扩散，防止羽流加速并减少羽流中的进一步混合。锋面过程增强了局部的混合，但对羽流的核心有一个未知的影响。这些过程中的每一个对羽流扩散和混合的贡献预计在很大程度上取决于羽流的规模。定量地了解这些过程的相对作用对于确定不同尺度的河流羽流对陆架环流和输运的动力作用是必要的。本建议的总体目标是更好地了解在河口附近运行的O（1 km）小尺度过程如何过渡到大尺度过程（O（100 km））浮力驱动的沿岸流通过O（10 km）的中间尺度。中心假设是，一套过程中的中场羽流修改羽流的传播和混合，从而近场和远场羽流之间的过渡。拟议的工作将确定一些关键机制在确定近场和中场羽流区域的空间和时间尺度方面的相对影响。它将限制在羽流的初始演变的总水团的修改，并帮助了解大陆架尺度的沿海流是如何形成的。将追求以下三个具体目标：1）量化阻止羽流扩散的过程，2）将减少的混合率与阻止羽流扩散联系起来，3）确定近场和中场区域的净混合。这种方法是必要的，以准确地描述和量化的物理过程，有助于混合在自然羽流的完整阵列，并确定如何在一个广泛的参数空间修改这些过程。在梅里马克河羽详细的现场测量将补充非旋转和旋转实验室实验和实验室和地球物理规模的数值模型实验。这项工作将填补一个重要的空白，淡水排放的能力，大规模的沿海ocean circulation.The更广泛的影响的研究是双重的：更好地了解河流羽流在沿海海洋学的作用，研究生和本科生的教育。这项研究将确定河流流入如何影响受羽流影响的大面积水域的水质，并为沿海管理人员提供更好的预测能力。它将资助三名研究生，三个参与机构各一名。 此外，实地活动将提供一个独特的学习经验，不仅为三个资助的研究生，但为其他研究生和本科生。使用一些小型船舶进行天气研究将需要研究生承担首席科学家的责任，对个别船只，提供了一个更大规模的物理海洋学领域的计划罕见的自主权和责任水平。

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.