An Ensemble‐Based Eddy and Spectral Analysis, With Application to the Gulf Stream
An Ensemble‐Based Eddy and Spectral Analysis, With Application to the Gulf Stream
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DOI：
10.1029/2021ms002692
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发表时间：
2021-03
影响因子：
6.8
通讯作者：
W. Dewar;Q. Jamet;T. Uchida;A. Poje
中科院分区：
文献类型：
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作者：
W. Dewar;Q. Jamet;T. Uchida;A. Poje
几十年来，人们认识到“涡旋”海洋一直是许多观测和理论研究的焦点。在这里，我们描述了一个概括的涡流能量的分析，使用合奏的基础上，解决了两个关键的相关问题：“涡流”的定义和能量谱的一般计算。一个系综将涡旋识别为流动的不可预测的成分，并允许在非均匀和非平稳设置中对其能量进行尺度分解。我们提出了两个不同的，但同样有效的，谱估计：一个是类似于经典的傅立叶谱，其他让人想起经典的经验正交函数分析。两者都满足Parseval等式，因此可以解释为长度尺度相关的能量分解。还讨论了传统方法中使用的数据“逐渐减少”或“窗口化”的问题。我们将分析应用于分离的北大西洋湾流的中尺度“分辨”（1/12°）集合。我们的研究结果揭示了墨西哥湾流和区域的高度各向异性的光谱与理论预期的光谱形状的协议和分歧。一般来说，我们发现光谱斜率下降的速度比准地转理论预期的最陡斜率要快。
The “eddying” ocean, recognized for several decades, has been the focus of much observational and theoretical research. We here describe a generalization for the analysis of eddy energy, based on the use of ensembles, that addresses two key related issues: the definition of an “eddy” and the general computation of energy spectra. An ensemble identifies eddies as the unpredictable component of the flow, and permits the scale decomposition of their energy in inhomogeneous and non‐stationary settings. We present two distinct, but equally valid, spectral estimates: one is similar to classical Fourier spectra, the other reminiscent of classical empirical orthogonal function analysis. Both satisfy Parseval's equality and thus can be interpreted as length‐scale dependent energy decompositions. The issue of “tapering” or “windowing” of the data, used in traditional approaches, is also discussed. We apply the analyses to a mesoscale “resolving” (1/12°) ensemble of the separated North Atlantic Gulf Stream. Our results reveal highly anisotropic spectra in the Gulf Stream and zones of both agreement and disagreement with theoretically expected spectral shapes. In general, we find spectral slopes that fall off faster than the steepest slope expected from quasi‐geostrophic theory.