Stokes drift fluctuations and upper ocean diffusion

斯托克斯漂移波动和上层海洋扩散

• 批准号: 1434864
• 负责人: Thomas Herbers
• 金额: $ 43.43万
• 依托单位: NorthWest Research Associates, Incorporated
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-02-01 至 2017-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1434864&HistoricalAwards=false
• 关键词: Stokes; drift; fluctuations; upper; ocean

The Lagrangian drift associated with ocean surface waves, known as Stokes Drift, plays an important role in the ocean surface boundary layer dynamics and in particular the small-scale (nominally a few kilometers) diffusion of passive tracers. Thus it is important for the break-up and dispersion of oil spills or sewage outflow, and transport of material in the upper ocean and near the coast in general. Considerable theoretical advances have been made over the last few decades, but the lack of direct observations hampers progress on the role of Stokes Drift in material transport in the upper ocean. The collection of new observations and development of theoretical and numerical models will advance the current understanding of these dynamics in realistic wave conditions in both the open ocean and the coastal environment. The nonlinear Lagrangian theory and sea surface kinematics simulations developed in this project will provide a general framework for the analysis and interpretation of measurements of surface-following moored buoys, drifters, and remote sensing systems. The findings from this study will provide a framework towards understanding and predicting wave-driven material transport processes, including the break-up of surface slicks and transport of larvae, and will contribute to more effective disaster mitigation and coastal ecology protection programs. The development of small, low-power, inexpensive drifters with satellite communication and sustainable energy sources, which can resolve both surface waves and surface drift fluctuations, is an important step toward more ambitious, global applications. Large arrays of these types of instruments can be used to monitor ocean waves, surf zone motions, mean surface currents, and surface temperature and salinity. A post-doctoral fellow will be trained in both observational and modeling techniques in the upper ocean and summer undergraduate interns will be exposed to the research process.The Lagrangian near-surface drift of ocean surface waves (Stokes Drift) is still poorly understood and no direct measurements have been reported. In particular, very little is known about random fluctuations in the Stokes Drift that are believed to be important to upper ocean diffusion processes. Detailed observations of the fluctuating surface drift in the upper ocean due to surface waves will be obtained, building on the investigators' recent development of small, wave-resolving drifters. Approximately 25 drifters will be deployed in homogeneous, open ocean conditions and in a more complex coastal environment with variable depth and currents, to observe the near surface kinematics and particle dispersion. To interpret the drifter data and develop a better understanding of the effects of nonlinearity and directional spreading on the surface drift and diffusion statistics, a Lagrangian theory for the surface kinematics in a random wave field will be developed. The theory will be extended to include random, small-scale medium variations (e.g. bottom topography and ambient currents), and augmented with direct numerical integration of the surface momentum balance to simulate more complex conditions with strong nonlinearity and/or rapid medium variations. Then, observations will be compared to theory and numerical simulations, and the relative contribution of Stokes Drift fluctuations to the observed particle diffusion will be evaluated to gain a better understanding of the role of waves in material transport and diffusion, both offshore and near the coast.

与海洋表面波相关的拉格朗日漂移，称为斯托克斯漂移，在海洋表面边界层动力学中起着重要作用，特别是被动示踪剂的小尺度（名义上几公里）扩散。因此，它对于石油溢漏或污水流出物的分解和分散，以及海洋上层和一般海岸附近物质的运输都很重要。在过去的几十年里，理论上取得了相当大的进展，但缺乏直接的观测阻碍了斯托克斯漂流在上层海洋物质运输中的作用。收集新的观测资料和开发理论和数值模型将促进目前对开阔海洋和沿海环境中现实波浪条件下这些动力学的理解。本项目中开发的非线性拉格朗日理论和海面运动学模拟将为表面跟随系泊浮标、漂流器和遥感系统的测量结果的分析和解释提供总体框架。这项研究的结果将为理解和预测波浪驱动的物质运输过程提供一个框架，包括表层浮油的破碎和幼虫的运输，并将有助于更有效的减灾和沿海生态保护计划。开发小型、低功耗、廉价的漂移器，配备卫星通信和可持续能源，可以解决表面波和表面漂移波动问题，是朝着更雄心勃勃的全球应用迈出的重要一步。这些类型的仪器的大型阵列可用于监测海浪，碎波带运动，平均表面电流，以及表面温度和盐度。一名博士后研究员将接受上层海洋观测和建模技术的培训，暑期本科实习生将接触研究过程，对海洋表面波的拉格朗日近表面漂移（斯托克斯漂移）仍然知之甚少，没有直接测量的报告。特别是，很少有人知道的随机波动的斯托克斯漂移，被认为是重要的上层海洋扩散过程。在调查人员最近开发的小型波浪分辨漂移器的基础上，将获得对上层海洋中由于表面波引起的波动表面漂移的详细观测。大约25个漂流器将部署在均匀、开阔的海洋条件下，以及深度和海流可变的更复杂的沿海环境中，以观察近地表运动学和粒子扩散。为了解释漂流数据并更好地理解非线性和定向传播对表面漂移和扩散统计的影响，将建立随机波场中表面运动学的拉格朗日理论。该理论将被扩展到包括随机的，小规模的介质变化（例如底部地形和环境电流），并增加了直接的数值积分的表面动量平衡，以模拟更复杂的条件下，强非线性和/或快速的介质变化。然后，观测结果将进行比较，理论和数值模拟，斯托克斯漂移波动所观察到的粒子扩散的相对贡献将进行评估，以获得更好地了解波浪在物质运输和扩散，离岸和海岸附近的作用。