Collaborative Research: Nonlinear Interactions between Surface and Internal Gravity Waves in the Ocean

合作研究：海洋表面重力波和内部重力波之间的非线性相互作用

• 批准号: 1634644
• 负责人: Kurt Polzin
• 金额: $ 21.24万
• 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: 2016
• 资助国家: 美国
• 起止时间: 2016-09-15 至 2020-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1634644&HistoricalAwards=false
• 关键词: Collaborative; Research; Nonlinear; Interactions; between

The action of the wind on the ocean surface transfers momentum, serves as a source of kinetic energy for both turbulence and waves and is a controlling factor of the structure of the ocean surface boundary layer. When wind blows over the ocean, the ocean responds in two significant ways. The first is that viscous shear stresses are communicated below the sea surface via transfer of turbulent momentum. The second is that the sea surface acquires an undulatory character as the pressure differences across the leading and trailing faces of surface waves transfer momentum via form drag. While the undulatory character of the ocean surface can be painfully obvious to the ocean scientist onboard a ship, effects such as mixing associated with surface gravity wave breaking, instabilities of the surface wave shear, and coupling of the surface wave?s Stokes drift with wind driven shear to form Langmuir circulations are ignored in standard ocean surface boundary layer models. Missing as well from these models is a representation of relatively high frequency internal waves that could be prone to breaking immediately below the mixed layer. This project seeks to broaden understanding of the connectivity between ocean surface boundary conditions and upper ocean mixing. The highly nonlinear multi-layer model and the numerical and analytical tools to be developed in this project could be useful for a wide range of physical problems in the upper ocean including shear instabilities and coherent features such as Langmuir vortices. It is also important to stress that small changes in the interior mixing coefficients in the tropical oceans can have an immense feedback on Sea Surface Temperature and, therefore, other physical quantities, including convection and precipitation, of climatological significance. This project will provide training in first principles understanding of nonlinear waves and their interactions to a graduate student and a post-doc in applied mathematics. Research training through their active participation in this cross-disciplinary collaboration will provide them a unique opportunity to broaden their research experience in physical oceanography and improve their understanding of the interplay between the two disciplines. Ocean observations and basic physical considerations point towards a paradigm of greatly enhanced transfers at high wind speeds, trapping in the upper ocean at buoyancy frequency turning points that allows a nonlinear equilibration process and interaction with lower frequency shear that promotes enhanced internal wave dissipation. This paradigm demands consideration of something more sophisticated than a resonant analysis. The objective of this project is to understand the role of surface gravity waves resulting in the nonlinear excitation of internal gravity waves and assessing the internal waves propensity for mixing the upper ocean. Three possible parameter regimes are proposed. At low wind speeds, transfers tend to be from the background Internal Gravity Wave (IGW) field to the Surface Gravity Wave (SGW) field. At high wind speeds, current theoretical predictions of SGW-IGW transfer rates are proportional to wind speed, i.e. a very sensitive dependence upon wind speed. Transfers reverse sign and energy is transferred from the SGW field to the IGW field. The change in sign denoting the transition from low-wind to high-wind conditions coincides with gale force wind conditions. Extrapolating such dependencies to gale force, let alone hurricane force, invalidates the validity of the nonlinear theory. A likely third parameter regime coincides with the breakdown of this theory. The proposed research consists of three coordinated efforts. The first is an observational study with the objectives of documenting the vertical structure of upper ocean turbulent dissipation relative to standard mixed-layer schemes and estimates of SGW-IGW transfers rates, and documenting the relationship of high frequency internal wave variability to wind and wave conditions. The second of the three efforts is to develop a highly nonlinear model for a multi-layer system, focusing on the three-layer (well-mixed upper, relatively thin transitional, and deep lower layers) case, without any limitations on wavelength scales, and to perform a numerical study, to investigate both resonant and non-resonant SGW-IGW interactions at finite amplitude. Questions of the onset of internal wave breaking and transition layer mixing will be addressed. The third effort is to construct a self-consistent finite amplitude analytic description of nonlinear SGW-IGW interactions using the proposed layered formulation. The proposed third approach is, by taking advantage of the canonical Hamiltonian structure of the model, to investigate the equilibration of the IGW field with SGW variability and how this equilibration changes at finite amplitude. Then, the numerical and analytic studies will be cross-validated and compared with the ocean observations.

风在海洋表面的作用传递动量，是湍流和波浪的动能来源，是海洋表面边界层结构的控制因素。当风吹过海洋时，海洋以两种重要的方式作出反应。首先，粘性剪切应力通过湍流动量的传递在海面以下传递。二是由于表面波前后面的压力差通过形式阻力传递动量，海面呈现波动特征。虽然海洋表面的波动特征对船上的海洋科学家来说是痛苦而明显的，但与表面重力波破裂相关的混合、表面波剪切的不稳定性以及表面波的耦合等影响？标准的海洋表面边界层模式忽略了Stokes漂移与风驱动切变形成的Langmuir环流。这些模型也缺少了相对高频的内波的表示，这些内波很容易在混合层下面立即破裂。该项目旨在扩大对海洋表面边界条件和上层海洋混合之间连通性的理解。高度非线性的多层模型以及在本项目中开发的数值和分析工具可用于解决海洋上层的各种物理问题，包括剪切不稳定性和朗缪尔涡旋等相干特征。还必须强调的是，热带海洋内部混合系数的微小变化可以对海表温度产生巨大的反馈，从而对包括对流和降水在内的其他具有气候意义的物理量产生巨大的反馈。该项目将为应用数学的研究生和博士后提供有关非线性波及其相互作用的第一性原理理解的培训。通过他们积极参与这一跨学科合作的研究培训，将为他们提供一个独特的机会，扩大他们在物理海洋学方面的研究经验，并提高他们对这两个学科之间相互作用的理解。海洋观测和基本的物理考虑指向了在高风速下传输大大增强的范例，在浮力频率转折点被捕获在海洋上层，允许非线性平衡过程和与低频切变的相互作用，促进增强的内波耗散。这种范式需要考虑比共振分析更复杂的东西。本项目的目的是了解表面重力波对内重力波非线性激发的作用，并评估内波对上层海洋混合的倾向。提出了三种可能的参数形式。在低风速下，传递倾向于从背景内重力波（IGW）场到表面重力波（SGW）场。在高风速下，目前对SGW-IGW传输速率的理论预测与风速成正比，即对风速的依赖非常敏感。传递反向符号，能量从SGW场传递到IGW场。标志的变化表示从低风到大风条件的转变与大风条件一致。将这种依赖关系外推到大风强度，更不用说飓风强度了，会使非线性理论的有效性失效。第三个参数可能与这一理论的崩溃相吻合。拟议的研究包括三个协调的努力。第一个是观测研究，目的是记录相对于标准混合层方案和SGW-IGW传输速率估计的上层海洋湍流耗散的垂直结构，并记录高频内波变率与风和波条件的关系。第二项工作是开发多层系统的高度非线性模型，重点关注三层（混合良好的上层，相对较薄的过渡层和较深的下层）的情况，不受波长尺度的限制，并进行数值研究，研究有限振幅下的谐振和非谐振SGW-IGW相互作用。讨论了内波破碎的发生和过渡层混合的问题。第三项工作是使用所提出的分层公式构建非线性SGW-IGW相互作用的自洽有限振幅分析描述。提出的第三种方法是利用模型的正则哈密顿结构，研究IGW场与SGW变异性的平衡以及这种平衡在有限振幅下如何变化。然后，将数值和解析研究结果与海洋观测结果进行交叉验证和比较。

项目成果

An Oceanic Ultra-Violet Catastrophe, Wave-Particle Duality and a Strongly Nonlinear Concept for Geophysical Turbulence

海洋紫外线灾难、波粒二象性和地球物理湍流的强非线性概念

• DOI: 10.3390/fluids2030036
• 发表时间: 2017
• 期刊: Fluids
• 影响因子: 1.9
• 作者: Polzin, Kurt L.;Lvov, Yuri
• 通讯作者: Lvov, Yuri