Near-N Internal Waves and Transition-Layer Mixing

近 N 内波和过渡层混合

• 批准号: 0927469
• 负责人: Jerome Smith
• 金额: $ 76.12万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-09-15 至 2013-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0927469&HistoricalAwards=false
• 关键词: Near; Internal; Waves; Transition; Layer

The oceanic mixed layer is crucial to air-sea exchange. The enhanced stratification at the base of the mixed layer (or 'transition layer') is also crucially important, as it affects the rate of mixed-layer deepening and mediates vertical exchanges between the mixed-layer and deeper ocean. Understanding the processes that control turbulent mixing of momentum and tracers in this transition layer is an outstanding problem in upper ocean physics. Based on new modeling results, we hypothesize that turbulent structures in an active mixed layer combined with inertial shear across the upper pycnocline can generate energetic Near-N Internal Waves (NNIW). These NNIW are confined to the region of elevated buoyancy frequency in the uppermost pycnocline, where they must eventually break and contribute their energy to turbulent dissipation and mixing. Two likely candidates for this kind of NNIW generation are Langmuir Cells and buoyancy-driven convection, both of which may generate waves by impinging on the stratified mixed-layer base. At the same time, the turbulence makes the eddy-viscosity in the surface layer large, which would damp these short internal waves. The project will look at the three-way interactions between the surface mixed layer, inertial shear, and high-frequency internal waves, and to examine the resulting effects on upper pycnocline mixing.Our approach combines numerical simulations (LES) that resolve both turbulent structures in the Mixed Layer (ML) and the NNIW generated in the upper pycnocline, along with detailed comparisons with suitable data collected over the past 2 decades. These data sets generally include estimates of length and time scales of the mixed layer motion, directional surface wave spectra, strain fields associated with NNIW, density profiles and overturns, velocity profiles over the upper few hundred meters, heat-flux estimates, and vector wind stress.The central questions are: How do high-frequency internal waves interact with mixed layer motions? and Do they affect entrainment and mixing in the upper pycnocline? An integral component is Large-Eddy Simulation (LES) modeling of the upper ocean, including wind and wave forced mixed layer motions, inertial shear, and the resulting NNIW in the stratified layer just below. The ultimate objective is to make in-depth data/model comparisons, more than on model development per se. However, some further model development is needed before comparisons with data can be realistic. The model-data comparison strategy involves data analogous re-sampling of model output and statistical comparisons. The anticipated results include improved understanding of upper ocean and surface layer mixing and dynamics, and hence improved models on all scales.Intellectual merit. The project focuses on a link in the air/ocean system that is vitally important yet incompletely understood: net mixing through the uppermost layers of the sea. The mixed layer and uppermost pycnocline together form a crucial barrier between the atmosphere and deepocean, controlling the net fluxes of heat, momentum, nutrients, and greenhouse gases. This uppermost layer is also vital to marine life, setting the scene where light and nutrients meet, and where pollutants and contaminants are dispersed. Appropriate scaling of these fluxes has been shown to be important to global air-sea coupled simulations, which can be sensitive to both the degree of surface mixing and to the ML depth.Broader impacts. The results will help improve air-sea exchange estimates, and hence both environmental and climate effects, thereby helping improve the information by which long-term policy decisions are made. The results and interpretations will be disseminated broadly to enhance scientific understanding and facilitate both decision making and further scientific work. The activity will provide training and scientific opportunities for a graduate student and a post-doc. Partnerships and collaborations across institutions will be actively developed. As an economic stimulus, salaries and supplies are spent locally and steadily; scientific equipment is by necessity selected for the highest quality with sustainable support and availability.

海洋混合层对海气交换至关重要。混合层（或“过渡层”）底部的增强分层也至关重要，因为它影响混合层加深的速度，并介导混合层和更深海洋之间的垂直交换。了解控制这一过渡层中动量和示踪剂湍流混合的过程是上层海洋物理学中的一个突出问题。基于新的模拟结果，我们假设，在一个活跃的混合层的湍流结构结合惯性剪切上密度跃层可以产生充满活力的近N内波（NNIW）。这些NNIW被限制在最上层密度跃层的浮力频率升高的区域，在那里它们最终必须打破并将其能量用于湍流耗散和混合。两个可能的候选人，这种NNIW代朗缪尔细胞和浮力驱动的对流，这两种可能会产生波的分层混合层的基础上碰撞。同时，湍流使近地层的涡粘性变大，这将对这些短内波产生阻尼。该项目将着眼于表面混合层，惯性剪切和高频内波之间的三向相互作用，并检查由此产生的影响上密度跃层mixing.Our方法结合数值模拟（LES），解决了在混合层（ML）和NNIW产生的上密度跃层，沿着与过去20年中收集的合适的数据进行详细的比较。这些数据集一般包括估计的长度和时间尺度的混合层运动，定向表面波频谱，应变场与NNIW，密度剖面和翻转，速度剖面在上几百米，热通量估计，矢量风stress.The中心问题是：如何高频内波与混合层运动相互作用？它们是否影响上层密度跃层的夹带和混合？一个不可或缺的组成部分是大涡模拟（LES）模拟上层海洋，包括风和波浪强迫混合层运动，惯性剪切，并在分层层中产生的NNIW就在下面。最终目标是进行深入的数据/模型比较，而不是模型开发本身。然而，在与数据进行比较之前，还需要进一步开发一些模型。模型-数据比较策略涉及模型输出的数据模拟重新采样和统计比较。预期成果包括增进对上层海洋和表层混合和动态的了解，从而改进所有尺度的模型。该项目的重点是空气/海洋系统中至关重要但尚未完全了解的一个环节：海洋最上层的净混合。混合层和最上层的密度跃层一起形成了大气和深海之间的重要屏障，控制着热量、动量、营养物质和温室气体的净通量。最上层对海洋生物也至关重要，它是光线和营养物质相遇的地方，也是污染物和污染物分散的地方。这些通量的适当缩放已被证明是重要的全球海气耦合模拟，这可能是敏感的表面混合的程度和ML深度。这些结果将有助于改进海气交换估计，从而改进环境和气候影响，从而有助于改进作出长期政策决定所依据的信息。结果和解释将广泛传播，以提高科学认识，促进决策和进一步的科学工作。该活动将为一名研究生和一名博士后提供培训和科学机会。将积极发展各机构之间的伙伴关系和协作。作为一种经济刺激措施，工资和供应品在当地稳定地支出;科学设备必须在可持续的支持和可用性下选择最高质量。