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.

近惯性波、中尺度涡旋和锋面在海洋中普遍存在。经典理论预测，快速的、不平衡的波和缓慢的、平衡的涡流之间的相互作用通常很弱。然而，一种新的理论表明，这种相互作用可以在锋生区域很强，在那里中尺度应变驱动一个跨锋非地转环流，并迅速加强热风切变。地转流的这种变化改变了存在的近惯性波的偏振关系，使它们的水平速度呈直线，并导致从涡旋中吸取动能的雷诺应力。涡旋传递的动能最终输往非地转环流，因此近惯性波对平衡的丧失起着催化作用。在这个过程中，波失去了所有的能量。基于一个简单的相互作用的理论模型的尺度参数表明，它可以发挥重要作用，在关闭近惯性波和涡旋的全球动能预算。然而，为了正确评估这一过程对全球能量平衡的影响，必须在没有空间均匀波前和波场模型中使用的简化假设的情况下理解该机制的物理学。该项目旨在通过对空间局部化的锋面和波场进行流体静力学和非流体静力学数值模拟来实现这一目标。将进行二维模拟，旨在研究波浪的变化并隔离波浪引起的平均流量变化。然而，这些将不允许平均流量的变化反馈到波浪动力学上。没有这种约束的三维流体静力学模拟将被用来调查这些反馈和量化的波浪引起的涡流动能的调整。将利用高分辨率非流体静力学模拟研究从波场和涡流场损失到假定的小尺度湍流的动能的最终命运。形成拟议研究基础的理论融合了锋面动力学、内波物理学和波平均流相互作用的研究，产生丰富的新现象，可能揭示地球物理流体动力学中的一个基本问题，即动能如何从平衡运动转移到不平衡运动并耗散。与此同时，这项工作提供了一个机制，在近惯性波场，一个问题是不完全理解的动能去除。更广泛的影响：拟议的研究解决了物理海洋学的突出问题之一？中尺度的动能是如何耗散的。这一点很重要，因为涡旋如何失去动能会影响它们的性质，从而影响大尺度环流和气候。该研究指出了一条途径，其中来自涡旋和内波的动能驱动锋面混合，对营养通量，初级生产力和水体转化产生影响。从这项研究中获得的见解将指导用于全球环流模式的涡旋和近惯性波耗散参数化的发展。该项目将用于培训一名研究生，并包括指导一名博士后研究员。研究成果将纳入讲座和外展活动中，激发人们对海洋环流的兴趣和魅力。