Near-Inertial waves

概述：海洋上的风产生的振荡称为近惯性波（NIW）。这些NIWs随后向下和向赤道方向传播，是风的机械能从表面传播到深海的主要途径。通过波与波的相互作用和散射，NIWs和内部潮汐为内部波带的其余部分提供能量。此外，NIWs控制着与整个海洋深处的破碎和混合有关的水柱的局部稳定性。内波频带的惯性频率是最低的，其准水平振荡运动对海面风应力和分层的阻抗很小，这是海洋中约占一半动能的NIWs占主导地位的主要动力学原因。由于它们对大气（风）强迫的挥发性响应，NIWs不能被描述为内部重力波的“通用”波谱的一部分，需要不同的方法和理论。知识价值：理论和计算方面的努力将针对与海洋近惯性波的产生和传播有关的三个问题：(A)近惯性波与地转平衡的涡流的相互作用，特别是涡流和近惯性波之间的能量交换；(b) NIWs的风力产生，β效应对涡旋涡度梯度在加速垂直辐射中的作用，以及海底坡度与波坡相当或大于波坡的海底地形反射NIWs；(c)地表重力波与NIWs的相互作用以及两种模态之间的风应力分配。上述过程控制着风对海洋内波场的作用速率、混合层近惯性振荡的阻尼以及NIWs向下和向赤道的辐射。这些机制在时间尺度上起作用，从几秒钟（重力波频率）到几周（地表增强的地转涡旋）。理论发展涉及多尺度分析、随机建模和平均。虽然参数化不是本项目的直接目标，但这里提出的面向过程的工作对于将内波物理纳入综合环流模型至关重要。更广泛的影响：海洋混合率不能以单一的普遍扩散率为特征，因此必须了解空间、时间和环境因素如何影响近惯性峰值的能量供应。这个峰值包含了决定与海洋混合有关的理查森数的大部分剪切方差。因此，这个问题对于模拟和诊断海洋在气候、海洋碳循环、向喜光带提供营养物质以及有意在深海处理碳和其他工业废物方面的作用至关重要。了解内部重力波在这种情况下的作用是该提案的长期目标。该项目涉及物理海洋学中当前重要问题的理论和数值模拟，适合物理海洋学家或工程师的博士论文。该项目涉及国际合作，并将有助于将阶段平均NIW模式附加到区域海洋模式系统。该项目将改进维基百科文章“斯托克斯漂移”，并将存根“科里奥利-斯托克斯力”扩展为完整条目。

Overview: The wind over the ocean generates oscillations called near-inertial waves (NIW). The subsequent downwards and equator-ward propagation of these NIWs is a main path for mechanical energy from the wind to travel from the surface into the deep ocean. Via wave-wave interactions and scattering, NIWs and internal tides energize the remainder of the internal wave band. Moreover, NIWs control the local stability of the water column that is relevant for breaking and mixing throughout the ocean's depths. A main dynamical reason for the dominance of NIWs which contain about half of the kinetic energy in the ocean is that the inertial frequency is the lowest available to the internal wave band, and the quasi-horizontal oscillatory motion of NIWs offers little impedance to surface wind stress and stratification. Because of their volatile response to atmospheric (wind) forcing, NIWs cannot be described as part of a "universal" wave spectrum of internal gravity waves and different approaches and theories are needed. Intellectual merit: A theoretical and computational effort will be directed at three problems related to the generation and propagation of ocean near-inertial waves (NIWs): (a) the interaction of NIWs with geostrophically balanced eddies, particularly the exchange of energy between eddies and NIWs; (b) the windy generation of NIWs, the role of the beta-effect versus eddy vorticity gradients in accelerating vertical radiation, and the reflection of NIWs from seafloor topography with bottom slopes that are comparable to, or larger than, the wave slope; (c) the interaction of surface gravity waves with NIWs and the partitioning of wind stress between the two modes during the generation process. The processes above control the rate at which the wind works on the ocean internal wave field, the damping of mixed-layer near-inertial oscillations and the downward and equatorward radiation of NIWs. These mechanisms act on time scales ranging from a few seconds (gravity wave frequencies) to weeks (surface-intensified geostrophic eddies). Theoretical developments involve multi-scale analysis, stochastic modeling and averaging. Although parameterization is not an immediate goal of this project, the process-oriented work proposed here is essential to the incorporation of internal-wave physics into comprehensive circulation models. Broader impacts: Ocean mixing rates cannot be characterized by a single universal diffusivity and thus it is essential to understand how spatial, temporal and environmental factors affect the supply of energy to the near-inertial peak. This peak contains most of the shear variance that determines Richardson numbers relevant for ocean mixing. Thus this problem is central to modeling and diagnosing the ocean's role in climate, the ocean carbon cycle, the nutrient supply to the euphotoic zone and the intentional deep-water disposal of carbon and other industrial waste products. Understanding the role of internal gravity waves in this context is a long-term goal of the proposal. The project involves both theory and numerical modeling on important current problems in physical oceanography suitable for a doctoral thesis for a physical oceanographer or an engineer. The project involves an international collaboration and will contribute to an effort to attach a phase-averaged NIW model to the Regional Ocean Model System. The project will improve the Wikipedia article "Stokes drift" and expand the stub "Coriolis-Stokes force" into a full entry.