Probing the Ocean's Multiscale Pathways

海洋流动是一个典型的多尺度系统，涉及整个连续空间长度和时间周期的过程和结构。尺度之间的非线性耦合，从数千公里的全流域环流到毫米大小的湍流涡旋，在理解和模拟海洋环流和混合方面存在重大困难，也限制了我们预测气候的能力。该项目的主要目标是利用卫星和高分辨率模型提供的数据，探测全球海洋中从10000公里到10公里左右的不同尺度的能量循环耦合。该项目采用了一种有点新颖的“粗粒化”方法来分析多尺度相互作用，比经典的“平均涡”分解更通用和强大。在数值模型中，几乎不可能直接将所有运动分解到最小尺度。相反，使用参数化来估计较小尺度对感兴趣的较大尺度环流的影响，参数化的选择通常取决于分辨尺度的截止点在哪里，有时取决于可以确定哪些物理过程是重要的特定位置。这项研究与“规模感知”和“位置感知”参数化的搜索相一致，这些参数化将普遍适用，而无需针对特定条件进行调整。该项目可能对气候科学中的一个基本问题产生直接影响：时间变率在多大程度上是流动系统本身中自然出现的，或者是对外部强迫的响应。这项工作还承诺提供先验的约束参数调整目前的计划，建议的计划，可适用于涡流允许的海洋模型，并将有助于发展一类新的海洋参数化的时间，位置和分辨率的函数。这项工作还将展示一种自洽的综合方法来分析和模拟多尺度系统的动态，这可能对气候以外的许多领域产生重要影响。为这项研究开发的多尺度分析代码将在Github上提供，以允许开放的开发方法。该项目将支持两名年轻的科学家，一个在她的博士学位的开始，另一个在他的职业生涯的门槛。最后，该项目的研究将通过罗切斯特博物馆和科学中心纳入外展工作。粗粒化有严格的数学基础，与成熟的物理技术密切相关，包括宏观电磁学，重整化群和大涡模拟。此外，与经典的分解，粗粒化是一致的粗分辨率气候模拟的参数化要求。控制球体上不同尺度动力学的方程可以相对容易地推导出来，为研究海洋流动中的多尺度路径开辟了一种新的和潜在的变革性方法，包括能量的传递，动量和示踪剂的运输，以及不同尺度的强迫-所有这些都可以在地理和时间上进行探索。该项目将分析不同路径和过程之间的地理和时间相关性，包括它们对大气强迫变化的振幅和频率响应。气候模式中需要参数化的物理过程取决于网格分辨率，也取决于对任何给定长度尺度上的主要过程的理解和量化。在这方面，该项目是理想的对齐，以推进一个新的系统的方法，以反映潜在的亚网格物理的“尺度感知”和“位置感知”参数化，沿着对不同长度的振幅和频率响应的更深入理解-该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的评估来支持。影响审查标准。

Oceanic flow is a quintessentially multiscale system, involving processes and structures over an entire continuum of spatial lengths and time periods. The nonlinear coupling between scales ranging from the many thousands of kilometers of basin-wide circulation down to the millimeter size of turbulent eddies presents a major difficulty in understanding and modeling oceanic circulation and mixing, and also in limiting our predictive ability to forecast climate. The main objective of this project is to probe the energy cycle coupling different scales from the order of 10000 km down to around 10 km in the global ocean, using data from satellites and high-resolution models. The project utilizes a somewhat novel ‘coarse-graining’ approach to analyze multiscale interactions that is more versatile and powerful than the classical ‘mean-eddy’ decomposition. It numerical models, it is almost never possible to directly resolve all motions down to the smallest scales. Instead, the influence of the smaller scales on the larger scale circulation of interest is estimated using parameterizations, whose choice typically depend on where the cut off for resolved scales are and sometimes on the particular location which may determine what physical processes are important. This research is aligned with the search for ‘scale-aware’ and ‘location-aware’ parameterizations, which would apply universally without needing to be tuned for specific conditions. The project can have a direct bearing on a fundamental problem in climate science: the extent to which temporal variability is naturally emergent within the flow system itself or is a response to external forcing. The work also promises to offer a priori constraints on parameter tuning of current schemes, on proposed schemes that may be applied to eddy permitting ocean models, and will help in the development of a new class of ocean parameterizations that are a function of time, location, and resolution. This work will also demonstrate a self-consistent integrated methodology to analyze and model the dynamics of multiscale systems, which can have an important impact on many fields beyond climate. The multiscale analysis codes developed for this study will be made available on Github to allow for an open development approach. The project will support two junior scientists, one at the beginning of her PhD and another at the threshold of his career. Finally, the project’s research will be integrated into outreach efforts through the Rochester Museum and Science Center.Coarse-graining has a rigorous mathematical foundation and is closely related to well-established physics techniques, including macroscopic electromagnetism, renormalization group, and large eddy simulation. Moreover, unlike the classical decomposition, coarse-graining is consistent with the parameterization requirements of coarse-resolution climate simulations. Equations governing the dynamics of different scales on the sphere can be derived relatively easily, opening up a new and potentially transformative way to studying multiscale pathways in oceanic flows, including the transfer of energy, transport of momentum and tracers, and forcing at different scales — all of which can be probed both geographically and temporally. This project will analyze the geographic and temporal correlations between different pathways and processes, including their amplitude and frequency response to changes in atmospheric forcing. The physical processes that require parametrization in climate models depend on the grid resolution and also on an understanding and quantification of the dominant processes at any given length-scale. In this respect, the project is ideally aligned to advancing a new systematic approach to ‘scale-aware’ and ‘location-aware’ parameterizations that reflect the latent subgrid physics, along with a deeper understanding of the amplitude and frequency responses of different length-scales and processes.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.