A Vortex Census from Lagrangian Floats

三个关键问题促使人们系统地重新研究拉格朗日浮子数据中的相干涡结构：(i)迫切需要将涡参数化方案以及涡解析数值模型与现场观测结果进行详细比较；（ii）最近根据卫星测高资料认识到，以前归因于罗斯比波的一大片变率似乎是由于一个高能非线性中尺度涡旋场，其内部特征在很大程度上仍是未知的；（三）越来越多地认识到连贯涡旋在流体输送和混合中所起的重要但多方面的作用，包括尺度太小而无法通过测高精确分辨的涡旋。这些问题都表明需要对相干涡旋场及其大尺度影响进行定量和综合研究。与此同时，湍流研究强调，目前理解海洋涡旋场的能力受到缺乏客观和理论上令人信服的途径的阻碍，无法从现有的拉格朗日数据推断欧拉“真理”——也就是说，目前无法从拉格朗日平台对涡旋性质和种群进行正式的普查。该项目将使用历史上深拉格朗日声学跟踪浮标集来量化漩涡特征、数量和在大范围内的动态影响。PI和合作者最近取得的一系列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、特别直接的联系。这项研究的出发点是能够客观地，在不确定性估计的情况下，从单个拉格朗日轨迹中提取连贯漩涡的详细时变方面。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，非齐次拉格朗日观测将被用于形成潜在欧拉场的估计，通过在理想化的准地转模拟中广泛测试的统计推断。目的是将涡旋分布描述为一个由少数参数控制的地理变化随机场。第三阶段和最后阶段量化了涡旋场对大尺度流动的影响——通过估计与涡旋相关的速度和涡度分布以及粒子和涡度输运。智力价值：这项研究将大大扩展和完善我们对海洋中连贯涡流作用的理解。通过分离构成“涡流通量”一般现象的一个过程，这将是朝着理解和量化小尺度“涡流”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建立和检验本身就是一个重要的贡献。更广泛的影响：这项工作的一个主要社会影响是它对我们预测长期气候变率的能力的潜在影响，因为它立即提高了我们根据原位数据评估涡旋分辨和非涡旋分辨数值模式的保真度的能力。从事该项目的博士后研究员将受益于接触新的分析技术和重要的拉格朗日数据集。浮动数据集的增值版本，以及本项目期间开发的所有分析软件，将按照附件中的数据管理计划免费分发给社区；这为研究海洋动力学打开了一扇新的窗口。

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.