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首页> 外文期刊>Journal of Physical Oceanography >Large-Eddy Simulation of Deep-Cycle Turbulence in an Equatorial Undercurrent Model
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Large-Eddy Simulation of Deep-Cycle Turbulence in an Equatorial Undercurrent Model

机译：赤道暗流模型中深循环湍流的大涡模拟

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摘要

Dynamical processes leading to deep-cycle turbulence in the Equatorial Undercurrent (EUC) are investigated using a high-resolution large-eddy simulation (LES) model. Components of the model include a background flow similar to the observed EUC, a steady westward wind stress, and a diurnal surface buoyancy flux. An LES of a 3-night period shows the presence of narrowband isopycnal oscillations near the local buoyancy frequency N as well as nightly bursts of deep-cycle turbulence at depths well below the surface mixed layer, the two phenomena that have been widely noted in observations. The deep cycle of turbulence is initiated when the surface heating in the evening relaxes, allowing a region with enhanced shear and a gradient Richardson number Ri_g less than 0.2 to form below the surface mixed layer. The region with enhanced shear moves downward into the EUC and is accompanied by shear instabilities and bursts of turbulence. The dissipation rate during the turbulence bursts is elevated by up to three orders of magnitude. Each burst is preceded by westward-propagating oscillations having a frequency of 0.004-0.005 Hz and a wavelength of 314-960 m. The Ri_g that was marginally stable in this region decreases to less than 0.2 prior to the bursts. A downward turbulent flux of momentum increases the shear at depth and reduces Ri_g. Evolution of the deep-cycle turbulence includes Kelvin-Helmholtz-like billows as well as vortices that penetrate downward and are stretched by the EUC shear.
机译：使用高分辨率大涡流模拟（LES）模型研究了导致赤道暗流（EUC）中深循环湍流的动力学过程。该模型的组成部分包括与观测到的EUC相似的背景流，稳定的向西风应力和日表面浮力通量。 3个晚上的LES显示在局部浮力频率N附近存在窄带等渗振荡以及在远低于表面混合层的深度夜间夜间深层湍流爆发，这是观测中广泛注意到的两种现象。当傍晚的表面加热放松时，便会产生深层的湍流，从而在表面混合层之下形成剪切力增强且理查森值Ri_g小于0.2的梯度区域。剪切力增强的区域向下移动到EUC，并伴有剪切力不稳定性和湍流爆发。湍流爆发期间的耗散率提高了三个数量级。每个脉冲串之前都有一个向西传播的振荡，该振荡的频率为0.004-0.005 Hz，波长为314-960 m。在突发之前，在该区域中略微稳定的Ri_g降低到小于0.2。向下的动量通量增加了深度处的剪切力并减小了Ri_g。深循环湍流的演变包括开尔文-亥姆霍兹状的波涛以及向下渗透并通过EUC剪切拉伸的涡流。

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  • 来源
    《Journal of Physical Oceanography》 |2013年第11期|2490-2502|共13页
  • 作者

    Hieu T. Pham; Sutanu Sarkar; Kraig B. Winters;

  • 作者单位

    Department of Mechanical and Aerospace Engineering, and Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California;

    Department of Mechanical and Aerospace Engineering, and Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California;

    Department of Mechanical and Aerospace Engineering, and Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California;

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