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Turbulence and internal waves in numerical models of the equatorial undercurrents system.

机译：赤道暗流系统数值模型中的湍流和内波。

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摘要

Direct Numerical Simulation (DNS) of simplified model problems is used to investigate the role of turbulence and internal waves in the Equatorial Undercurrents (EUC) system. Prior observational studies of the Pacific EUC have established a strong correlation between deep-cycle turbulence in the thermocline and internal waves. The object of the thesis is to understand and quantify the dynamical processes underlying turbulence and internal waves in the EUC. The investigation has three phases. In the first phase, an idealized problem of a weakly-stratified shear layer located above a thermocline is simulated to investigate internal waves excited by unstable shear. The evolution of the shear layer consists of coherent Kelvin-Helmholtz (KH) rollers and small-scale turbulence. Internal waves excited by the KH rollers are narrow-band and of stronger amplitude than that of the broadband wave field generated by turbulence. Internal waves are shown to carry significant amount of momentum and energy away from the shear layer. In the second phase, the EUC is represented by a weakly stratified shear layer on top of a stable stratified jet. The objective is to investigate the interaction between the jet and the waves excited by the adjacent shear layer. Two simulations are performed: one with the jet located far from the shear layer (far jet) and the other with the shear layer on top of the jet (near jet). In the far jet, waves excited by the KH rollers are reflected and trapped in the region between the shear layer and jet and lead to little dissipation. In the near jet, more representative of the EUC configuration, waves with wavelength larger than that of the KH rollers are found in and below the jet. Pockets of hot fluid associated with horseshoe vortices that originate from the shear layer penetrate into the jet region, initiate turbulence and disrupt the internal wave field. In the third final phase of the thesis, a stratified jet situated below a well-mixed surface layer driven by a constant wind stress and a surface buoyancy flux is considered. Turbulence is generated in the surface layer and deepens into the jet upper-flank. Waves generated by the turbulent surface layer propagate downward across the jet. The momentum flux and energy flux carried by the waves are significantly weaker than the waves generated by the unstable shear in the problem studied during the first phase. Intermittent patches of intense dissipation inside the jet upper-flank are the result of ejections of fluid parcels.
机译：简化模型问题的直接数值模拟（DNS）用于研究湍流和内波在赤道暗流（EUC）系统中的作用。先前对太平洋EUC的观测研究已经建立了热跃层深层湍流与内部波之间的强相关性。本文的目的是了解和量化EUC中湍流和内部波动的动力学过程。调查分为三个阶段。在第一阶段，模拟了位于温跃层上方的弱分层剪切层的理想化问题，以研究不稳定剪切激发的内部波。剪切层的演变包括相干的开尔文-亥姆霍兹（KH）辊和小规模的湍流。与湍流产生的宽带波场相比，由KH辊激发的内部波具有较窄的频带和更强的振幅。内波显示出从剪切层带走了大量的动量和能量。在第二阶段，EUC以稳定分层射流顶部的弱分层剪切层为代表。目的是研究射流与相邻剪切层激发的波之间的相互作用。进行了两种模拟：一种是使射流远离剪切层（远射流），另一种是使剪切层位于射流顶部（近射流）。在远射流中，由KH滚子激发的波在剪切层和射流之间的区域中被反射和捕获，并导致很小的耗散。在更能代表EUC配置的近射流中，在射流之内和之下都发现波长大于KH辊的波。与来自剪切层的马蹄形涡流相关的热流体囊渗入射流区域，引发湍流并破坏内部波场。在论文的第三个最后阶段，考虑了分层射流，该射流位于由恒定风应力和表面浮力通量驱动的充分混合的表层之下。湍流在表层产生，并加深到射流的上侧面。由湍流表面层产生的波在射流上向下传播。在第一阶段研究的问题中，波浪携带的动量通量和能量通量比不稳定剪切产生的波浪要弱得多。射流上部侧面内部间歇性的强力消散斑块是流体小包喷射的结果。

著录项

  • 作者

    Pham, Hieu T.;

  • 作者单位

    University of California, San Diego.;

  • 授予单位 University of California, San Diego.;
  • 学科 Physical Oceanography.Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 208 p.
  • 总页数 208
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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