Horizontal dispersion of near-inertial oscillations in a turbulent mesoscale eddy field
Horizontal dispersion of near-inertial oscillations in a turbulent mesoscale eddy field
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DOI：
10.1357/002224001762674908
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发表时间：
2001-09
影响因子：
0.5
通讯作者：
P. Klein;S. G. L. Smith
中科院分区：
文献类型：
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作者：
P. Klein;S. G. L. Smith
本文研究了以连续波数谱为特征的全湍流斜压中尺度涡场中风致近惯性振荡的频散。利用垂直正模展开分析了涡旋电场对不同NIO模水平色散的影响。以前的研究已经确定了两种色散制度：捕获和强色散。我们在物理和光谱空间检查模式，以评估哪种制度盛行。数值和分析结果表明了一种诱捕机制的普遍存在。对于每一种NIO模式，都存在一个临界水平波数kc，将以俘获为主的大规模NIO结构与以强色散为主的能量低得多的小规模NIO结构分开。在接近kc的尺度上，最大的分散效率将NIO动能集中在这些尺度上。波数ck是折射和色散平衡的结果。这种平衡发生在最高的波数处。此后，kc（尺寸表达式为kc25 p/(ftrm2)）随时间以与考虑斜压NIO模式的变形半径Rm成反比的速率减小。因此，在任何给定时间，较高的NIO斜压模态能量主要集中在小尺度负涡度结构中，例如在锐涡度锋附近的e段，而较低的NIO模态能量则集中在中尺度反气旋涡旋的核心内。在大时间内，饱和机制将k - c的时间演化停止在接近QG -e低场动能谱峰值的值。
We study the dispersion of wind-induced near-inertial oscillations (NIOs) in a fully turbulent baroclinic mesoscale eddy e eld characterized by a continuous wavenumber spectrum. The ine uence of the eddy e eld on the horizontal dispersion of the different NIO modes is analyzed using a vertical normal mode expansion. Previous studies have identie ed two dispersion regimes: trapping and strong dispersion. We examine the modes in physical and spectral space to assess which regime prevails. Numerical and analytical results show the prevalence of a trapping regime. For each NIO mode, there exists a critical horizontal wavenumber, k c, that separates large-scale NIO structures, where trapping dominates, from the much less energetic small-scale NIO structures, where strong dispersion dominates. The maximum efe ciency of dispersion for scales close to k c concentrates NIO kinetic energy at these scales. The wavenumber k c results from a balance between refraction and dispersion. This balance e rst occurs at the highest wavenumber. Thereafter, kc, which has dimensional expression kc 2 5 p/( ftRm 2 ), decreases with time at a rate inversely proportional to the radius of deformation, Rm, of the baroclinic NIO mode considered. As a consequence, at any given time, higher NIO baroclinic mode energy can mostly be found in small-scale negative vorticity structures, such as e laments near sharp vorticity fronts, whereas lower NIO mode energy is concentrated within the core of mesoscale anticyclonic vortices. For large times, a saturation mechanism stops the time-evolution of k c at a value close to the peak of the kinetic energy spectrum of the QG e ow e eld.