The life cycle of internal waves in the ocean: effects of currents and modulational instabilities

内波是非线性色散波的一种，200多年来一直是流体力学研究的一个重要领域。当重力恢复力作用于垂直位移的流体时，它们存在于密度分层流体的内部。海洋中近一半的内波能量的来源是潮汐流，它推动着流体上下倾斜的水深线，如大陆斜坡和洋脊。近几十年来，人们花费了大量的精力来了解这种波源的时空分布，以及波浪传播时的命运。内波在将能量从大尺度转移到小尺度以及影响海洋环流和生产力的热量和营养物质的垂直混合方面发挥着基本作用。它们可以远距离输送流体和粒子。它们的水流可以重新悬浮沉积物并冲击近海结构。已经观察到鱼类在响应大内波的通过时垂直迁移，以优化它们的觅食策略。内波可以从产生地点传播数千公里，因此在一个地方产生的波可以对很远的地方产生影响。内波有多种形式，包括垂直传播和水平传播的内波束以及水平传播的内波模式。梁是在接近临界的底部斜坡处产生的，并被假设在塑造大陆架方面起作用。水平传播波包括波长为0 (100)km的内潮，它可以演变成内孤立波。我的研究目标是：(i)确定背景流如何通过潮汐-地形相互作用影响内波的产生，以及内波如何与洋流和涡流相互作用；（ii）研究由内波引起的跨大陆架运输；（iii）调查水平传播内波包的演变，以确定流氓（异常大）内波可能形成的条件以及包如何可能破裂。这项研究将使用二维和三维数值模拟和理论的结合。它将包括理想化的过程研究和基于观察的数值模拟。理论模型将用于理解这些模型模拟的复杂波场，并且由于它们相对简单和快速，通常需要更充分地探索参数空间。研究的地点包括安哥拉和秘鲁大陆架，这是重要的渔业所在地，以及亚马逊大陆架。这项研究将有助于海洋资源的管理，并提高我们预测海洋当前和未来状况的能力。我的研究团队成员将获得高性能计算方面的宝贵专业知识，包括数据分析和可视化，以及处理复杂问题的技能。

Internal waves are examples of nonlinear-dispersive waves, the study of which has been a fascinating and important area of research in fluid dynamics for over 200 years. They exist in the interior of density-stratified fluids when gravitational restoring forces act on vertically displaced fluid. The source of close to half of the internal wave energy in the oceans is tidal currents pushing fluid up and down sloping bathymetry such as the continental slopes and ocean ridges and in recent decades a lot of effort has been expended in understanding the spatial and temporal distribution of this wave source and on the fate of the waves as they propagate away. Internal waves play a fundamental role in transferring energy from large to small scales and in the vertical mixing of heat and nutrients impacting ocean circulation and productivity. They can transport fluid and particles over large distances. Their currents can re-suspend sediments and impact offshore structures. Fish have been observed to migrate vertically in response to the passing of large internal waves to optimize their feeding strategy. Internal waves can propagate thousands of kilometers from their generation site so wave generation in one location can have an impact at great distances. Internal waves appear in many forms including vertically and horizontally propagating internal wave beams and horizontally propagating internal wave modes. Beams are generated at near-critical bottom slopes and have been hypothesized to play a role in shaping the continental shelf. Horizontally propagating waves include internal tides with wavelengths of O(100) km which can evolve into internal solitary waves. My research objectives are to (i) determine how background currents affect internal wave generation by tide-topography interactions and how internal waves interact with ocean currents and eddies; (ii) investigate cross-shelf transport by internal waves; and (iii) to investigate the evolution of horizontally propagating internal wave packets to determine the conditions under which rogue (unusually large) internal waves may form and how the packets may break down. The research will use a mixture of two- and three-dimensional numerical modelling and theory. It will include idealized process studies and numerical simulations based on observations. Theoretical models will be used to understand the complex wave field simulated by these models and, because of their relative simplicity and speed, are often required to more fully explore a parameter space. Sites studied include the Angolan and Peruvian Shelves which are locations of important fisheries, and the Amazon Shelf. This research will contribute to the management of ocean resources and the improvement of our ability to predict the current and future state of the ocean. Members of my research team will gain valuable expertise in high-performance computing, including data analysis and visualization, and skills in working on complex problems.