Collaborative Research: Rapid Gravitational Adjustment of Horizontal Shear: A Recipe for Energetic Mixing in the Coastal Ocean

本研究将通过全面考察水平密度对比下水平剪切流的稳定性和演化，扩展我们对沿海海洋混合过程的认识。这种剪切和分层的配置在沿海海洋的强时间依赖性流动中很常见，包括河口流入和流出，海岬和岛屿周围的分离流，以及形态复杂区域（如潮汐入口）的合并流。由此产生的浮力驱动的流动导致剪切流涡旋的倾斜和强烈拉伸，最终导致流动的破裂，导致强烈的垂直混合。水平剪切作用下的水平分层具有强烈增强混合的潜力，尽管重力驱动的流动本身也增加了垂直分层。对这一过程的动力学和后果的研究将涉及高分辨率非流体静力数值模拟和利用粒子图像测速和激光诱导荧光的综合实验室实验。这种高度非线性进化的尺度论点已经发展起来，并将指导研究。预计这些结果将为未来沿海海洋环流模式中至关重要的混合过程的参数化提供信息。沿海混合过程对污染物的运输和稀释、生产海岸带营养物质和碳的生物地球化学循环以及海洋幼虫和浮游生物的运输都很重要。这项研究的结果将有助于改进混合的参数化，这些参数化可以纳入河口水质、沿海海洋环流和生态模型。两位pi都积极参与各自的学术项目（MIT/WHOI联合项目和UNC海洋科学），这项研究的结果将很快进入课堂。该资助还将为本科生和研究生提供重要的早期职业支持，并将通过WHOI暑期学生奖学金计划和WHOI地球物理流体动力学（GFD）暑期计划纳入研究的各个方面。这笔拨款将支持WHOI GFD实验室的继续运作，该实验室在过去30年中接待了100多名访问学生和科学家，进行物理海洋学、大气动力学、流体动力学和地质过程等各种实验。

Intellectual Merit The study will extend our knowledge of mixing processes in the coastal ocean through a comprehensive examination of the stability and evolution of horizontally sheared flows in the presence of a horizontal density contrast. This configuration of shear and stratification is common in strongly time-dependent flows in the coastal ocean including estuarine inflows and outflows, separating flows around headlands and islands, and merging flows in morphologically complex regions such as tidal inlets. The resulting buoyancy-driven flow results in tilting and intense stretching of the shear-flow vortices and ultimately a breakdown of the flow leading to intense vertical mixing. Horizontal stratification in the presence of horizontal shear has the potential to strongly enhance mixing, despite the fact that the gravity-driven flow by itself increases the vertical stratification. The research into the dynamics and consequences of this process will involve both high-resolution non-hydrostatic numerical modeling and comprehensive laboratory experiments utilizing particle image velocimetry and laser-induced fluorescence. Scaling arguments for this highly nonlinear evolution have been developed and will guide the investigation. It is expected that the results will inform future parameterizations of mixing processes that are crucial in coastal ocean circulation models. Broader Impacts Coastal mixing processes are important for pollutant transport and dilution, biogeochemical cycles of nutrients and carbon in the productive coastal zone, and the transport of marine larvae and plankton. The results of this study will yield understanding that should lead to improved parameterizations for mixing that can be incorporated into estuarine water quality, coastal ocean circulation, and ecological models. The PIs are both active in their respective academic programs (MIT/WHOI Joint Program and UNC Marine Science) and the results of this research will quickly reach the classroom. The grant will also provide important early career support for undergraduate and graduate students will be incorporated into aspects of the research through the WHOI Summer Student Fellowship Program and the Geophysical Fluid Dynamics (GFD) Summer Program at WHOI. The grant will support the continued operation of the WHOI GFD Laboratory, which has hosted over 100 visiting students and scientists over the last 30 years to undertake a variety of experiments spanning physical oceanography, atmospheric dynamics, fluid dynamics, and geological processes.