A New Mechanism for Generation of Internal Waves

海洋内波对垂向水混合的效率、污染物和悬浮物的输送有很大影响。它们产生剪切流和湍流，将水混合在一起，并将营养物质从深渊提供给表面光层。这些影响反过来对盆地的初级生物生产力和水质起着重要作用。本研究将研究一种新的内波产生机制，这种机制可能发生在河水侵入海洋时。最近在河流羽流区域拍摄的一系列新的卫星图像显示，有证据表明，表面重力流的头部在从内波被强大的河流排放有效阻止的超临界演变制度过渡到释放内波时产生了内波。现场测量表明，这种内波产生机制在产生幅度与总水深相当的内波方面是相当有效的，但到目前为止还没有从理论上进行研究。这一事实是本研究的一个强烈动机。该提案旨在通过对汉堡大学海洋学研究所收集的卫星图像进行分析，并开发一个先进的数值模式并将其应用于哥伦比亚河羽流，填补在控制不断传播的河流羽流正面产生内波的物理过程方面的认识空白，自2003年以来收集和公布了关于该河羽流的独特观测数据。这一基本目标的实现将导致对重力流到内波再到湍流的能量转移机制的理解。

Oceanic internal waves have great implications for the efficiency of vertical water mixing, transport of pollutants and suspended matter. They produce shear currents and turbulence that mix water and supply nutrients from the abyss to the surface photic layer. These effects, in turn, play a major role in primary biological productivity and water quality of the basins. The present study will examine a new mechanism for internal wave generation which may occur at the intrusion of river waters into the sea. New series of satellite images taken recently in the areas of river plumes revealed an evidence of generation of internal waves by the head of a surface gravity current during its transition from a suprcritical regime of evolution when internal waves are effectively arrested by strong river discharge, to a subcritical one when they are released. In-situ measurement have shown that this mechanism of internal wave generation is quite effective at producing internal waves with amplitudes comparable with the total water depth, however it has not bee studied theoretically so far. This fact was a strong motivation for the present study. The proposal aims to fill the gap in understanding of physical processes controlling the internal wave generation at the frontal side of propagating river plume through the analysis of satellite images collected by the Institute of Oceanography of the University of Hamburg and through the development of an advanced numerical model and its application to the Columbia River plume, for which unique observational data were collected and published since 2003. The achievement of this basic goal will lead to an understanding of the mechanism of energy transfer from the gravity current to internal waves, and then to turbulence.