Collaborative Research: Three-Dimensional Surfzone Eddies

合作研究：三维表面区涡流

• 批准号: 1061692
• 负责人: Stephen Henderson
• 金额: $ 43.18万
• 依托单位: Washington State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-06-01 至 2016-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1061692&HistoricalAwards=false
• 关键词: Collaborative; Research; Three; Dimensional; Surfzone

Surfzone eddies mix pollutants, erode coast- lines, endanger swimmers, and transport marine organisms. Eddies may be directly forced by groups of breaking surface gravity waves, or may develop as shear instabilities of mean alongshore currents ('shear production'). The relative importance of direct forcing and shear production has not yet been determined, but recent numerical simulations suggest that wave group forcing may be an important, yet mostly neglected, factor. Surfzone eddies have often been viewed as two-dimensional and depth-independent, but recent observations indicate that eddies can in fact be strongly three-dimensional. Indeed, observed three-dimensionality can be so strong that total shear production cannot be calculated unless depth-dependence is resolved. This study will examine the dynamics of three-dimensional surfzone eddies using depth-resolving field observations and numerical modeling.A 15-element array of Acoustic Doppler Current Profilers (ADCPs) will be deployed to gather the first synoptic, vertically-resolved observations of surfzone mean currents and eddies. ADCP observations will be used in conjunction with a numerical model that will take advantage of recently developed 3D wave forcing formulations, while also simulating eddy generation by wave groups. Shear production and direct forcing terms in the eddy energy equation will be evaluated in a range of numerical simulations, and in observations, to determine their relative importance under a variety of incident-wave conditions. The project will provide the first horizontally-resolved in-situ observations of near-surface eddy motions. In addition to quantifying magnitudes, phasing, and de-correlation across-shore, the team will test whether alongshore propagation speeds and de-correlation distances vary in the vertical (both vary across-shore). These observations will be compared with simulations. Numerical simulations and observations, especially vertical phasing and coherence with wave groups, will be examined to distinguish vertical shear generated by breaking from shear generated by bottom friction or horizontal advection. Simulations will be used to study the effects of three- dimensionality on mixing, including possible rapid lateral mixing of passive tracers and momentum.This experiment will build on substantial existing resources, including Washington State University experience working with ADCPs, and Oregon State University expertise in three-dimensional circulation modeling. Deployment and recovery will carried out by one of the world's best-equipped field crews at the US Army Corps of Engineers' Field Research Facility. Broader Impacts: This project will improve our understanding of the nearshore eddies that mix pollutants and organisms, transport sediments, and endanger swimmers. A community model for predicting nearshore currents and eddies will be tested and refined and made available to the community, constituting an important step towards the goal of a predictive model for surfzone pollution. Such a model would be valuable to managers, who must currently rely on bacterial cultures that are slow to return actionable results. Field data, constituting the first depth-resolving synoptic measurements of surfzone mean currents, and the first profiling array to extend 1 km from the shore to the inner shelf, will be made available to the oceanographic community. Three graduate students will be funded. To disseminate knowledge beyond universities, students will likely partner with high school teachers (through Washington State University's GK-12 program) and PIs will partner with a community college teacher (facilitated by the COSEE program).

冲浪带漩涡混合污染物，侵蚀海岸线，危及游泳者，并运送海洋生物.涡旋可能是由破碎的表面重力波群直接产生的，也可能是由于平均沿岸流的剪切不稳定性（“剪切产生”）而产生的。直接强迫和切变产生的相对重要性尚未确定，但最近的数值模拟表明，波群强迫可能是一个重要的，但大多被忽视的因素。冲浪带漩涡通常被视为二维和深度无关，但最近的观测表明，漩涡实际上可以是强烈的三维。事实上，观察到的三维性可以是如此之强，总的剪切生产无法计算，除非深度依赖性是解决。本研究将利用水深分辨观测和数值模拟方法研究三维岸滩涡的动力学特征，并利用15单元声学多普勒海流剖面仪（ADCPs）阵列首次获得岸滩平均海流和涡的天气学、垂直分辨观测数据。ADCP观测将与数值模型结合使用，该模型将利用最近开发的三维波浪强迫公式，同时还模拟波群产生的涡流。剪切生产和直接强迫条款的涡能量方程将在一系列的数值模拟，并在观测中进行评估，以确定其相对重要性在各种入射波条件下。该项目将提供第一个水平分辨率的近地表涡流运动的现场观测。除了量化幅度，定相和跨海岸去相关外，该团队还将测试沿岸传播速度和去相关距离是否在垂直方向上变化（两者都在跨海岸变化）。这些观察结果将与模拟结果进行比较。数值模拟和观测，特别是垂直相位和波群的相干性，将被检查，以区分垂直剪切产生的破碎从底部摩擦或水平平流产生的剪切。模拟将用于研究三维对混合的影响，包括被动示踪剂和动量的可能的快速横向混合。该实验将建立在大量现有资源的基础上，包括华盛顿州立大学使用ADCP的经验，以及俄勒冈州州立大学在三维环流模拟方面的专业知识。部署和回收工作将由世界上装备最好的战地工作人员之一在美国陆军工程兵部队的实地研究设施进行。更广泛的影响：该项目将提高我们对近岸涡流的了解，这些涡流混合污染物和生物、输送沉积物并危及游泳者。将测试和完善一个用于预测近岸水流和涡流的社区模型，并提供给社区使用，这是朝着建立一个冲浪带污染预测模型的目标迈出的重要一步。这样一个模型对管理者来说很有价值，因为他们目前必须依赖细菌培养，而细菌培养的结果很慢。将向海洋学界提供实地数据，这些数据构成对冲浪带平均海流的第一次深度分辨天气测量，以及从海岸延伸到内大陆架1公里的第一个剖面阵列。将资助三名研究生。为了在大学之外传播知识，学生可能会与高中教师合作（通过华盛顿州立大学的GK-12项目），PI将与社区大学教师合作（由COSEE项目提供便利）。