The Influence of Mesoscale Eddies on the Internal Tide
The Influence of Mesoscale Eddies on the Internal Tide
复制标题
中尺度涡旋对内潮汐的影响
DOI：
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
M. Dunphy
中科院分区：
文献类型：
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作者：
M. Dunphy
正压潮汐在M2频率上耗散了2.5 TW的能量。海底地形是造成这种耗散的部分原因，内潮的产生也是部分原因。这种能量的命运在很大程度上是通过非线性波-波相互作用从大尺度到小尺度的级联来描述的，在那里它被耗散。本论文旨在探讨海洋中尺度涡旋（涡）的存在如何影响内潮。以前的工作着眼于正压潮汐与涡旋的相互作用。Krauss（1999）发现，这种相互作用可以产生调制的内潮，但尺度分析表明，这种影响可能没有报告的那么强。MITgcm用于模拟地形上正压气流产生的内波，并与Lamb博士的IGW模式进行了比较。斜压涡旋是通过分析规定的，然后也使用MITgcm进行地转调整。最后，将两者结合起来，并分析了内部潮汐场的存在和不存在的各种大小和长度尺度的漩涡。本次调查的结果并没有发现一个强大的模式之间的能量转移，能量的模式分布在内部潮汐保持不变时，涡流被添加。然而，当内波通过涡旋时，涡旋尾流中会产生内波的聚焦束和阴影束，这些束的强度变化很大，垂直积分能流在阴影区几乎为零，而在聚焦区增加一倍以上。水平流场的模态分解表明，模式2和3波是最强烈的影响，涡和强烈的贡献的光束的形成。模式1似乎受涡流的影响较小。模式1的较大波长和较快的群速度支持涡流与它的相互作用较少的概念。
The barotropic tide dissipates a well established estimate of 2.5 TW of energy at the M2 frequency. Bottom topography is responsible for part of this dissipation, and the generation of the internal tide is also partly responsible. The fate of this energy is largely described by a cascade from large scales to small scales by nonlinear wave-wave interactions where it gets dissipated. This thesis aims to investigate how the presence of mesoscale eddies (vortices) in the ocean affect the internal tide. Previous work has looked at the interaction of the barotropic tide with eddies. Krauss (1999) found that the interaction can produce a modulated internal tide, however a scaling analysis suggests that the effect may not be as strong as reported. The MITgcm is used to simulate internal wave generation by barotropic flow over topography and comparisons are made with Dr. Lamb’s IGW model. Baroclinic eddies are analytically prescribed and then geostrophically adjusted also using the MITgcm. Finally, the two are combined, and the internal tide field is analysed with and without the presence of eddies of various magnitude and length scales. The results of this investigation do not find a strong transfer of energy between modes; the modal distribution of energy in the internal tide remains the same when an eddy is added. However, focusing and shadow beams of internal waves are produced in the wake of an eddy as the internal waves pass through it. The beams show very strong variations in intensity, vertically integrated energy flux can reduce almost to zero in the shadow regions and increase more than double in the focusing regions. Modal decomposition of the horizontal flow field reveals that mode 2 and 3 waves are most strongly affected by the eddies and contribute strongly to the formation of the beams. Mode 1 appears to be less affected by the eddy. The larger wavelength and faster group velocity of mode 1 supports the notion that the eddy interacts with it less.