A Vortex Census from Lagrangian Floats

拉格朗日浮子的涡旋普查

• 批准号: 1235310
• 负责人: Jonathan Lilly
• 金额: $ 72万
• 依托单位: NorthWest Research Associates, Incorporated
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2017-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1235310&HistoricalAwards=false
• 关键词: Vortex; Census; Lagrangian; Floats

Three key issues motivate a systematic re-examination of coherent vortex structures in Lagrangian float data: (i) a pressing need for detailed comparison of eddy parameterization schemes, as well as of eddy-resolving numerical models, against in situ observations; (ii) the recent recognition, based on satellite altimetry, that a large swath of variability previously attributed to Rossby waves instead appears due to an energetic nonlinear mesoscale eddy field, the interior signature of which is as yet largely unknown; and (iii) an increasing appreciation of the important but multifaceted role coherent eddies play in fluid transport and mixing, including eddies at scales too small to be accurately resolved by altimetry. These issues all point to the need for a quantitative and integrated study of the coherent eddy field and its large-scale impacts. At the same time, turbulence studies emphasize that the current ability to understand the oceanic vortex field is hampered by the lack of an objective and theoretically compelling avenue for inferring Eulerian "truths" from available Lagrangian data - that is, the inability to currently perform a formal census of vortex properties and populations from the Lagrangian platform. This project will quantify vortex characteristics, populations, and dynamical impacts across a broad range of scales using the historical set of deep Lagrangian acoustically tracked floats. A series of recent advances by the PI and collaborators make such a study possible, providing a new and particularly direct link between Lagrangian observations and vortex dynamics. The starting point for the study is the ability to extract, objectively and with uncertainty estimates, detailed time-varying aspects of coherent eddies from individual Lagrangian trajectories. The first phase of this project utilizes this method to describe vortex currents as they appear in the data. In this second phase, inhomogenous Lagrangian observations will be used to form estimates of underlying Eulerian fields, via statistical inference backed by extensive testing within idealized quasigeostrophic simulations. The goal is to describe the vortex distribution as a geographically-varying random field controlled by a small number of parameters. The third and final phase quantifies impacts of the vortex field on the large-scale flow - by estimating the velocity and vorticity distributions as well as particle and vorticity transport associated with the eddies.Intellectual Merit: This study will substantially extend and refine our understanding of the role of coherent eddies in the ocean. It will be an important step towards the larger goal of understanding and quantifying the impact of small-scale "eddy" processes on the large-scale circulation, by isolating one of the processes that make up the general phenomenon of "eddy fluxes". Addressing the connection to observations from satellite altimetry is particularly timely. The construction and testing of a Lagrangian vortex census statistical methodology is itself an important contribution.Broader Impacts: A primary societal impact of this work is its potential impact on our ability to predict long-term climate variability by immediately increasing our ability to assess the fidelity of both eddy-resolving and non-eddy-resolving numerical models against in situ data. The postdoctoral researcher working on the project will benefit from exposure to novel analysis techniques and an important Lagrangian data set. Value-added versions of the float dataset, and all analysis software developed during this project, will be freely distributed to the community as described in the attached Data Management Plan; these open a new window into ocean dynamics.

有三个关键问题促使系统地重新研究拉格朗日浮动数据中的相干涡旋结构：(1)迫切需要将涡旋参数化方案以及涡旋解析数值模式与现场观测进行详细比较；(2)最近根据卫星测高技术认识到，以前归因于Rossby波的大范围变率似乎是由于高能的非线性中尺度涡场而出现的，其内部特征在很大程度上尚不清楚；(3)人们越来越认识到相干涡流在流体输送和混合中发挥的重要但多方面的作用，包括尺度太小而无法通过高度计准确分辨的涡流。这些问题都表明，需要对相干涡旋场及其大范围影响进行定量和综合研究。与此同时，湍流研究强调，由于缺乏从现有拉格朗日数据推断欧拉“真相”的客观和理论上令人信服的途径，目前理解海洋涡旋场的能力受到阻碍--也就是说，目前无法从拉格朗日平台对涡旋特性和人口进行正式普查。该项目将使用历史上的一组深度拉格朗日声学跟踪浮标来量化涡旋特征、种群和大范围内的动力影响。PI及其合作者的一系列最新进展使这样的研究成为可能，在拉格朗日观测和涡旋动力学之间提供了一种新的和特别直接的联系。这项研究的出发点是能够客观地从单个拉格朗日轨迹中提取相关涡旋的详细时变方面，并进行不确定的估计。该项目的第一阶段利用这种方法来描述数据中出现的涡流。在第二阶段，非均匀拉格朗日观测将被用来形成对基本欧拉场的估计，通过理想化的准地转模拟中的广泛测试支持的统计推断。目标是将涡旋分布描述为受少量参数控制的随地理变化的随机场。第三个阶段也是最后一个阶段，通过估计涡旋的速度和涡度分布以及与涡旋相关的颗粒和涡度传输，量化涡旋场对大尺度流动的影响。智力上的优点：这项研究将极大地扩展和完善我们对海洋中相干涡旋作用的理解。通过分离构成“涡流”这一普遍现象的过程之一，这将是朝着理解和量化小尺度“涡旋”过程对大尺度环流的影响这一更大目标迈出的重要一步。处理与卫星测高观测的联系尤其及时。拉格朗日涡旋普查统计方法的构建和测试本身就是一项重要贡献。广泛影响：这项工作的主要社会影响是它对我们预测长期气候变异性的能力的潜在影响，因为它立即提高了我们根据现场数据评估涡旋解析和非涡旋解析数值模式的保真度的能力。从事该项目的博士后研究人员将受益于接触新的分析技术和重要的拉格朗日数据集。如所附数据管理计划所述，浮标数据集的增值版本以及在该项目期间开发的所有分析软件将免费分发给社区；这为了解海洋动态打开了一扇新的窗口。