Collaborative Research: Internal Lee-Wave Dissipation in Oceanic Flows with Mean Shear

消散海洋平衡流的机制仍然不确定，但对正确模拟海洋环流很重要。已经提出，通过内部背风波产生以及随后的湍流产生的耗散占所需损失的20-75%。然而，微观结构的测量不同意预测的耗散。这项研究将解释这种差异，并更好地限制背风波在消散与重新分配能量中的作用。本研究将进行数值模拟，描述在地球旋转引起的有限范围流动占主导地位的地区，内部背风波的产生，传播，耗散和重吸收。该项目的成果将在会议上介绍，并在同行评审的期刊上发表，以便更广泛的科学界可以使用。这项研究的结果将提供一个改进的参数化的耗散和再分配的平衡流和诱导混合的背风波生成，并提高海洋环流模拟的准确性。该项目将支持一名研究生在数值建模和内波物理学方面的教育和指导，以及一名本科生在研究方面的教育和指导。该研究还将用于面向公众和K-12科学教师的推广活动，以及本科生和国际学生的培训。大量的功率，相当于1 TW，被认为是通过风工作输入海洋环流。稳态条件的维持（即，恒定的能量水平）要求通过能量耗散过程平衡风增加的能量。内部背风波生成被认为是最大的预测能量汇之一，通过湍流生成耗散0.2至0.75 TW。然而，南极绕极流射流的测量发现，湍流耗散率达不到预测的数量级。最近的数值模拟的自发近惯性波产生的黑潮锋发现，所产生的波能量被重新吸收回平均流。如果背风波也发生再吸收，那么它们将是重新分配平衡能量的机制，而不是耗散平衡能量的机制。这些数值模拟将确定哪些部分的背风波能量损失于湍流，而哪些部分被再吸收到平均流中，从而确定背风波的产生是否代表大尺度环流的主要汇。缺少的关键要素是剪切流和波浪作用（E/w）守恒，其中E是波浪能量密度，w = kU是背风波的拉格朗日频率，k是地形波数，U是流速。在底部增强的旋转剪切流中，分数kU 1/（kUo）用于耗散，分数（kUo-kU 1）/（kUo）用于再吸收，其中Uo是底部流速，U1 f/k是波浪破碎处的流动。数值模拟将测试现实的海洋流动和地形配置，以确定是否再吸收是一个显着的一部分，在海洋中的背风波generation.This奖项反映了美国国家科学基金会的法定使命，并已被认为是值得的支持，通过评估使用基金会的知识价值和更广泛的影响审查标准。

The mechanisms for dissipating the ocean's balanced flow remain uncertain but are important for correctly simulating oceanic circulation. Dissipation through internal lee-wave generation followed by turbulence production has been proposed to account for 20-75% of the needed loss. However, microstructure measurements do not agree with the predicted dissipation. This research will explain this discrepancy and better constrain the role of lee-waves in dissipating vs. redistributing energy. This study will carry out numerical simulations describing the generation, propagation, dissipation, and reabsorption of internal lee-waves in areas where earth rotation-induced flows of finite extent are dominant. Results from this project will be presented at conferences and published in peer-reviewed journals to make them available to the wider scientific community. The results of this study will provide an improved parameterization for the dissipation and redistribution of balanced flows and induced mixing by lee-wave generation and increase the accuracy of Ocean circulation modeling. The project will support education and mentoring of a graduate student in numerical modeling and internal-wave physics, and an undergraduate student in research. The research will also be utilized in outreach activities for the general public and K-12 science teachers, as well as undergraduate and international student training.Large amounts of power, equivalent of 1 TW, is thought to be input into the ocean circulation by wind-work. The maintenance of steady state conditions (i.e., constant energy levels) in the world's oceans requires that addition of energy by the wind is balanced through energy dissipation processes. Internal lee-wave generation has been assumed to be one of the largest predicted energy sinks dissipating 0.2 to 0.75 TW through turbulence generation. However, measurements in Antarctic Circumpolar Current jets find that turbulent dissipation rates fall short of predictions by as much as an order of magnitude. Recent numerical simulations of spontaneous near-inertial wave generation in the Kuroshio Front find that much of the generated wave energy is reabsorbed back into the mean flow. If reabsorption also occurs for lee waves, they would be as much a mechanism for redistributing balanced energy as dissipating it. These numerical simulations will determine what fractions of lee-wave energy are lost to turbulence vs. being reabsorbed into the mean flow and hence address whether lee-wave generation represents a major sink for the large-scale circulation. Missing key elements have been sheared flow and wave action (E/w) conservation where E is the wave energy density, w = kU the Lagrangian frequency of the lee wave, k the topographic wavenumber and U the flow speed. In a bottom-intensified rotating shear flow, the fraction kU1/(kUo) is available for dissipation and (kUo- kU1)/(kUo) for reabsorption, where Uo is the bottom flow speed and U1 f/k the flow where the waves break. The numerical simulations will test realistic ocean flow and topography configurations to determine whether reabsorption is a significant fraction of lee-wave generation in the ocean.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.