Stokes drift fluctuations and upper ocean diffusion

与海洋表面波有关的拉格朗日漂移，称为斯托克斯漂移，在海洋表面边界层动力学，特别是被动示踪剂的小尺度(名义上是几公里)扩散中起着重要作用。因此，对于溢油或污水外流的分解和扩散，以及一般情况下在上层海洋和沿海附近的材料运输来说，这一点很重要。在过去的几十年里，理论上已经取得了相当大的进展，但缺乏直接观测阻碍了斯托克斯漂移在上层海洋物质运输中的作用的进展。新观测资料的收集以及理论和数值模型的发展将促进目前对公海和沿海环境中现实波浪条件下的这些动力学的理解。本项目开发的非线性拉格朗日理论和海面运动学模拟将为分析和解释水面跟随系泊浮标、漂浮器和遥感系统的测量数据提供一个一般框架。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，包括表面浮油的分解和幼虫的运输，并将有助于更有效的减灾和海岸生态保护计划。开发具有卫星通信和可持续能源的小型、低功率、廉价的漂移器，可以解决表面波和表面漂移波动，是朝着更雄心勃勃的全球应用迈出的重要一步。这类仪器的大量阵列可以用来监测海浪、海浪带运动、平均表面流以及表面温度和盐度。一名博士后将在上层海洋接受观测和建模技术培训，夏季本科生实习生将接触到研究过程。海洋表面波的拉格朗日近水面漂移(斯托克斯漂移)仍然知之甚少，还没有直接测量的报道。特别是，人们对斯托克斯漂移中的随机波动知之甚少，这些随机波动被认为对上层海洋扩散过程很重要。在研究人员最近开发的小型波浪分辨漂移器的基础上，将获得对由于表面波引起的上层海洋中波动表面漂移的详细观测。大约25个漂流者将被部署在均匀、开阔的海洋条件下，以及在深度和水流可变的更复杂的沿海环境中，观察近表面的运动学和颗粒扩散。为了解释漂移数据，并更好地了解非线性和定向扩散对表面漂移和扩散统计的影响，将发展随机波场中表面运动学的拉格朗日理论。该理论将扩展到包括随机的小尺度介质变化(例如海底地形和周围洋流)，并通过直接对表面动量平衡进行数值积分来模拟具有强烈非线性和/或快速介质变化的更复杂的条件。然后，将把观测结果与理论和数值模拟进行比较，并评估斯托克斯漂移波动对观测到的粒子扩散的相对贡献，以更好地了解波浪在近海和海岸附近物质运输和扩散中的作用。

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.