Eddy-internal wave interactions in regions of frontogenesis

锋生区域中的涡-内波相互作用

• 批准号: 1260312
• 负责人: Leif Thomas
• 金额: $ 52.68万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-04-01 至 2018-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1260312&HistoricalAwards=false
• 关键词: Eddy; internal; wave; interactions; regions

Near-inertial waves, mesoscale eddies, and fronts are ubiquitous in the ocean. Classical theory predicts that the interaction between the fast, unbalanced waves and the slow, balanced eddies is usually weak. A new theory demonstrates, however, that this interaction can be strong in regions of frontogenesis, where mesoscale strain drives a cross-front ageostrophic circulation and rapidly intensifies thermal wind shear. This change in geostrophic flow modifies the polarization relation of near-inertial waves that are present, making their horizontal velocity rectilinear, and resulting in a Reynolds stress that draws kinetic energy from the eddies. The kinetic energy transferred from eddies is ultimately lost to the ageostrophic circulation, hence the near-inertial waves play a catalytic role in loss-of-balance. In the process the waves lose all of their energy. Scaling arguments based on a simple theoretical model for the interaction suggest that it could play a significant role in closing the global kinetic energy budgets for both near-inertial waves and eddies. To correctly assess the impact of this process on global energy balances, however, the physics of the mechanism must be understood without the simplifying assumption used in the model of a spatially homogeneous front and wave field. This project aims to do this using a hierarchy of hydrostatic and non-hydrostatic numerical simulations of spatially localized fronts and wave fields. Two dimensional simulations will be performed that are designed to study the modifications of the waves and isolate the wave-induced changes to the mean flow. These will not, however, allow the changes in mean flow to feedback on the wave dynamics. Three-dimensional hydrostatic simulations without this constraint will be used to investigate these feedbacks and quantify the wave-induced adjustments to the eddy kinetic energy. The ultimate fate of the kinetic energy lost from the wave and eddy fields to presumably small-scale turbulence will be investigated with high-resolution non-hydrostatic simulations.Intellectual Merit: The theory that forms the basis of the proposed research merges studies of frontal dynamics, internal wave physics, and wave mean flow interactions, yielding rich new phenomena that may shed light on one of the fundamental problems in geophysical fluid dynamics of how kinetic energy is transferred from balanced to unbalanced motions and dissipated. At the same time, the work provides a mechanism for the removal of the kinetic energy in the near-inertial wave field, a problem that is not fully understood.Broader Impacts: The proposed research tackles one of the outstanding questions in physical oceanography ? how the kinetic energy in the mesoscale is dissipated. This is important because how eddies lose their kinetic energy affects their properties, with consequences for the large-scale circulation and hence climate. The research points to a pathway where kinetic energy from eddies and internal waves drives mixing at fronts, with implications for nutrient fluxes, primary productivity, and water mass transformation. Insights from this study will guide the development of parameterizations for the dissipation of eddies and near-inertial waves for use in global circulation models. The project will be used to train a graduate student and includes mentoring of a postdoctoral researcher. The research results will be incorporated into lectures and outreach activities that provoke interest and fascination in the ocean circulation.

近乎惯性的波浪，中尺度的涡流和前部在海洋中无处不在。经典理论预测，快速，不平衡的波和缓慢，平衡的涡流通常很弱。然而，一种新的理论表明，这种相互作用在额叶发生区域可能很强，其中中尺度的菌株驱动跨前期的循环循环并迅速增强热风剪。地质流动的这种变化改变了存在的近惯性波的极化关系，从而使它们的水平速度直线性变化，并导致雷诺应力，从而从涡流中吸引动能。从涡流传递的动能最终会失去年龄的循环，因此近惯性波在平衡中起催化作用。在此过程中，海浪损失了所有能量。基于简单的理论模型的缩放论点表明，它在关闭近惯性波和涡流的全球动能预算中可能发挥重要作用。但是，为了正确评估该过程对全球能量平衡的影响，必须理解机制的物理，而无需在空间均匀的前沿和波场模型中使用的简化假设。该项目的目的是使用空间局部局部和波场的静水和非静态数值模拟的层次结构来实现这一目标。将进行二维模拟，旨在研究波浪的修饰并隔离波诱导的平均流量变化。但是，这些不会允许平均流量的变化以对波动力学的反馈。没有这种约束的三维静水压模拟将用于研究这些反馈并量化波诱导的对涡流能量的调整。高分辨率的非静态模拟的高分辨率的优点：构成拟议的研究的基础，构成了额叶的动态，内部波动相互作用，在一定的地位上，可能会出现质量的新型，从而使一项的基础上的动态相互作用，从波浪和涡流损失到可能是小规模的湍流中的动能的最终命运将进行研究。动能如何从平衡转移到不平衡的运动并消散。同时，这项工作提供了一种在近惯性波场中去除动能的机制，这个问题尚未完全理解。Broader的影响：拟议的研究解决了物理海洋学中的重要问题？如何消散中尺度的动能。这很重要，因为涡流如何失去动能会影响其性质，这对大规模循环和因此气候产生了影响。该研究指向了一条途径，其中涡流和内波的动能在前面驱动混合，对营养通量，一级生产力和水量转化具有影响。这项研究的见解将指导参数化的发展，以耗散涡流和近惯性波，以用于全球循环模型。该项目将用于培训研究生，并包括指导博士后研究员。研究结果将纳入引起海洋循环的兴趣和迷恋的讲座和外展活动中。