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; 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.

海滩和相邻的表面受到地面污染的威胁，陆地污染通常会排入海岸线，并在海岸线上运输并分散在表面上（海岸线附近的浪潮区域）。污染的水会导致昂贵的海滩封闭和危害公共卫生，但目前尚无对冲浪区污染的预测模型，这种模型所需的表面性分散率尚不清楚。否则现场工作发现Surfzone Tracer（例如污染，污染，养分，幼虫，幼虫）的分散与在水平埃德兹内的强度相关。观察结果和模型结果表明，表面涡流的大小和时间尺度范围很广，但是这种丰富的涡度（旋转）场的结构和起源尚不清楚。这项研究将使用独特的圆形电流仪表，使第一个河道（0.05-0.25 Hz）和在自然海滩上的一系列入射波条件下，表面垂直涡度的表面垂直涡度（例如，从水平涡流）进行较低的频率测量。 2011年进行的试点测试表明，循环阵列测量值可用于估计频率范围内的涡度，这将允许测试平均涡度随着平均波角和波浪高增加的假设增加，并且随着波动方向扩散，平均波角和波高而，涡度方差随着波动方向的增加而增加。表面涡度有许多潜在的来源。特别是，假设涡度是在断裂波峰的末端（波峰末端）产生的，并且最近的建模研究表明，波峰末端可能是表面涡流扩散的主要强迫机制。在这里，将将表面涡度测量与视频观测值结合使用，以量化波峰期间事件期间涡度变化的变化，并估计波峰端涡度的产生。在一系列条件下，将将波峰末端强制涡度与其他可能的涡流强迫机制（包括波 - 均值和沿岸电流（剪切波）的剪切不稳定性）进行比较。将表面式肠膜（平方涡度）光谱与理论光谱形状进行比较，并可能表明一级搅拌量表。Broader的影响：这种涡度的研究将增加对Surfzone Eddies和混合的了解，并可能仅使用视频观察或外距离海外波浪条件进行涡流扩散估计。扩散率估计是为了建模表面污染，从而改善公共安全和海滩管理决策所必需。与高中老师合作，​​团队将领导与学生进行实地考察和讨论，并将创建有关符合国家科学教育标准的表面过程的课程，并可以适应不同的学习水平。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），因此可以在WHSTEP和全国范围内使用它。