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，危害游泳者，并运输海洋生物。涡旋可能是由一组破碎的表面重力波直接强迫的，也可能发展为近岸平均流的切变不稳定(切变产生)。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、但大多被忽略的因素。Surfzone旋涡通常被认为是二维的，与深度无关，但最近的观测表明，旋涡实际上可以是强烈的三维旋涡。事实上，观测到的三维性可能非常强，除非深度相关性得到解决，否则无法计算总的剪切产量。这项研究将利用深度分辨率现场观测和数值模拟来研究三维表面带涡旋的动力学。将部署一个由15个单元组成的声学多普勒海流剖面仪(ADCP)阵列来收集第一批垂直分辨率的表面带平均流和涡流的天气学观测。ADCP观测将与一个数值模式结合使用，该模式将利用最近开发的3D波浪强迫公式，同时还模拟按波群产生的涡流。涡旋能量方程中的切变产生项和直接强迫项将在一系列数值模拟和观测中进行评估，以确定它们在各种入射波条件下的相对重要性。该项目将提供对近地表涡旋运动的第一次水平分辨率的现场观测。除了量化横跨海岸的震级、相位和去相关外，研究小组还将测试近岸传播速度和去相关距离是否在垂直方向上有所不同(两者都在沿海有所不同)。这些观测结果将与模拟结果进行比较。将研究数值模拟和观测，特别是垂直相移和与波群的一致性，以区分由破裂产生的垂直切变和由底部摩擦或水平平流产生的切变。模拟将被用来研究三维对混合的影响，包括可能的被动示踪剂和动量的快速横向混合。这个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与ADCP合作的经验，以及俄勒冈州立大学在三维环流建模方面的专业知识。部署和恢复将由世界上装备最好的野战人员之一在美国陆军工程兵团的野战研究设施进行。更广泛的影响：这个项目将提高我们对近岸涡流的理解，这些涡流混合了污染物和生物，输送了沉积物，并危及游泳者。将对预测近岸海流和涡流的社区模型进行测试和改进，并向社区提供，这是朝着实现冲浪区污染预测模型目标迈出的重要一步。这样的模式对管理者来说将是有价值的，他们目前必须依赖细菌培养，这些细菌培养很慢才能产生可操作的结果。将向海洋界提供实地数据，这些数据构成了对海面带平均流的第一次深度分辨天气学测量，以及第一个从海岸延伸到内陆架1公里的剖面阵列。三名研究生将获得资助。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计划)，个人投资机构将与社区大学教师合作(由COSEE计划促进)。