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

海洋平衡流动的消散机制仍然不确定，但对于正确模拟海洋环流是重要的。通过内部背风波产生和湍流产生的消散被认为占所需损失的20%-75%。然而，微观结构测量结果与预测的耗散并不一致。这项研究将解释这种差异，并更好地限制背风波在能量消散和再分配中的作用。这项研究将进行数值模拟，描述有限范围的地球自转诱导流动为主的地区内背风波的产生、传播、耗散和重吸收。该项目的成果将在会议上公布，并在同行评议的期刊上发表，以便向更广泛的科学界提供这些成果。研究结果将为平衡流的耗散和再分配以及背风波的诱导混合提供一个改进的参数化法，并提高海洋环流模拟的精度。该项目将支持对一名数值建模和内波物理研究生以及一名本科生进行研究的教育和指导。这项研究还将用于普通公众和K-12科学教师的外联活动，以及本科生和国际学生的培训。据悉，大量电力，相当于1太瓦，通过风能输入到海洋循环中。要维持世界海洋的稳定状态(即恒定的能级)，就需要通过能量耗散过程平衡风能的增加。内部背风波的产生被认为是最大的预测能量汇之一，通过湍流产生耗散0.2-0.75TW。然而，对南极绕极水流的测量发现，湍流的消散率比预测的要低一个数量级。最近对黑潮锋面自发近惯性波产生的数值模拟发现，产生的波能大部分被重新吸收到平均流中。如果背风波也发生重吸收，它们将既是一种消散平衡能量的机制，也是一种重新分配平衡能量的机制。这些数值模拟将确定背风波能量的哪一部分损失到湍流中，而不是被重新吸收到平均流中，从而确定背风波的产生是否代表着大尺度环流的一个主要汇。缺失的关键要素是切变流动和波作用(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是水流速度。在底部强化的旋转剪切流中，分数kU1/(Kuo)可用于消散，(Kuo-kU1)/(Kuo)可用于再吸收，其中Uo为底流速度，U1f/k为波浪破碎处的流动。数值模拟将测试真实的海洋流动和地形配置，以确定重吸收是否在海洋中的背风波产生中占很大比例。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.