Short-crested Breaking Waves and Surfzone Vorticity

短顶破碎波和海带涡度

• 批准号: 1232910
• 负责人: Steve Elgar
• 金额: $ 85万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1232910&HistoricalAwards=false
• 关键词: Short; crested; Breaking; Waves; Surfzone

Beaches and the adjacent surfzone are threatened by terrestrial pollution that often drains onto the shoreline where it is transported and dispersed within the surfzone (region of breaking waves near the shoreline). Polluted water causes costly beach closures and endangers public health, but currently there are no predictive models for surfzone pollution and the surfzone dispersion rates required for such a model are not known.Recent fieldwork has found surfzone tracer (e.g., pollution, nutrients, larvae) dispersion is correlated with the strength of horizontal eddies within the surfzone. Observations and model results indicate there is a wide range of surfzone eddy sizes and time scales, but the structure and origin of this rich vorticity (rotation) field is unknown. This study will use a unique circular array of current meters to make the first sea-swell (0.05-0.25 Hz) and lower frequency measurements of surfzone vertical vorticity (e.g., from horizontal eddies) over a range of incident wave conditions on a natural beach. A pilot test done in 2011 suggests the circular array measurements can be used to estimate vorticity over a wide frequency range, which would allow the testing of the hypotheses that mean vorticity increases with mean wave angle and wave height, and that vorticity variance increases with wave directional spread, mean wave angle, and wave height. There are many potential sources of surfzone vorticity. In particular, it is hypothesized that vorticity is generated at the ends of a breaking wave crest (crest ends), and a recent modeling study suggests that crest ends may be a primary forcing mechanism for surfzone eddy diffusion. Here surfzone vorticity measurements will be combined with video observations to quantify changes in vorticity during crest-end events, and to estimate crest-end vorticity generation. Crest-end forced vorticity will be compared with other possible eddy forcing mechanisms, including wave groups and shear instabilities of the mean alongshore current (shear waves), over a range of conditions. The surfzone enstrophy (squared vorticity) spectrum will be compared with theoretical spectral shapes and may indicate a primary stirring scale.Broader Impacts:This investigation of vorticity will increase knowledge of surfzone eddies and mixing, and may lead to eddy diffusivity estimates using only video observations or offshore wave conditions. Diffusivity estimates are necessary to model surfzone pollution, and thus to improving public safety and beach management decisions.The results of this work and the team's field experiences will be shared with high school oceanography and coastal studies students through the Woods Hole Science and Technology Education Partnership (WHSTEP). In collaboration with a high school teacher the team will lead fieldtrips and discussions with students, and will create a lesson on surfzone processes that fits within National Science Education Standards and can be adapted to different learning levels. A website will be developed to host the finished self-contained product (lesson plans, presentations, activities, and assessments) so it can be used by educators in the WHSTEP and across the nation.

海滩和邻近的冲浪带受到陆地污染的威胁，这些污染往往排到海岸线上，在那里被输送并分散在冲浪带（海岸线附近的碎波区域）内。受污染的水导致昂贵的海滩关闭并危及公众健康，但目前还没有用于冲浪带污染的预测模型，并且这种模型所需的冲浪带分散率也不知道。污染物、营养物、幼虫）的扩散与冲浪带内水平涡流的强度有关。观测和模式结果表明，有一个广泛的冲浪区涡的大小和时间尺度，但结构和起源，这丰富的涡度（旋转）场是未知的。这项研究将使用一个独特的海流计圆形阵列，进行第一次海浪（0.05-0.25 Hz）和较低频率的冲浪区垂直涡度测量（例如，来自水平涡流）在自然海滩上的入射波条件范围内。2011年进行的一项试点试验表明，圆形阵列测量可用于估计宽频率范围内的涡度，这将允许测试以下假设：平均涡度随平均波角和波高而增加，涡度方差随波向扩展、平均波角和波高而增加。冲浪带涡度有许多潜在来源。特别是，它是假设涡产生在一个破碎的波峰（波峰端）的两端，最近的建模研究表明，波峰端可能是一个主要的强迫机制surfzone涡扩散。在这里，冲浪带涡度测量将与视频观测相结合，以量化在波峰结束事件的涡度变化，并估计波峰结束涡度生成。波峰末端强迫涡度将与其他可能的涡流强迫机制进行比较，包括波群和平均沿岸流（剪切波）的剪切不稳定性，在一系列条件下。的surfzone涡度拟能（平方涡度）频谱将与理论的频谱形状进行比较，并可能表明一个主要的搅拌scale.Broader影响：涡度的调查将增加知识surfzone涡和混合，并可能导致涡扩散估计只使用视频观测或离岸波条件。扩散率的估计是必要的模型冲浪带污染，从而提高公共安全和海滩管理decisions.The这项工作的结果和团队的实地经验将通过伍兹霍尔科学和技术教育伙伴关系（WHSTEP）与高中海洋学和沿海研究的学生分享。在与高中教师合作，该团队将带领实地考察和讨论与学生，并将创建一个符合国家科学教育标准，并可以适应不同的学习水平的冲浪区过程的教训。将开发一个网站来托管完成的独立产品（课程计划，演示，活动和评估），以便WHSTEP和全国各地的教育工作者可以使用。