Deep ocean internal wave generation in weak stratification

PI：Crockett，Julie Proposal number：1606040海洋中的盐分浓度随深度而变化。这一事实在水中产生了被称为内波的波。这些海浪的破裂驱动了深海中的大部分混合，定义了污染物、温室气体、海洋营养物的混合速率，并维持了平衡的温度分布。据估计，维持关键的海洋混合需要2.1太瓦的混合功率。据推测，超过一半的必要能量来自于潮汐在崎岖地形上产生的内波。海浪通过与其他海浪和洋流的相互作用进行传播，直到它们转化为更小规模的破碎海浪。这项提议的重点是利用实验室实验来研究内波的产生过程，并了解内波是如何在海洋系统内产生和传播的。这项研究的发现可能会导致新的大规模海洋模式的发展，这些模式对于预测水生生物的迁徙模式、预测污染物在海洋中的扩散(如福岛事故放射性泄漏的扩散)以及预测天气和气候模式都很重要。内波产生的一个意想不到的因素是，潮汐在地形上流动，在地形上层结太弱，不能直接在地形上方产生内波，但在层化增加的地区，可以在地形上方很高的地方观察到内波。这些波浪可能有助于将潮汐能量从大尺度转化为小尺度，这对波浪破碎和由此产生的混合具有重要的环境后果。这里提出的工作是一项实验和分析工作，目的是描述一种相对未被探索的内波产生方法--在弱层结区域(预计内波不会传播)的地形上由于潮汐流动而产生的内波，这些内波辐射到强层结区域，这意味着要描述整个海洋的内波能量谱。建议：1)利用实验探索在两层层结剖面中均匀流和潮流在地形上产生的内波；2)表征层结廓线的变化对内波产生的影响，其中对于所有层结剖面，地形都处于弱层结区域，因此不预期内波，上面具有较强的层结；以及3)建立从地形通过可变层结的能量传播的分析模型，包括代表瞬逝到传播波的区域。该项目将有助于实验方法的发展和对分层流动动力学的理解，这将为大规模模拟系统提供信息，从而更好地估计波浪的产生、传播和消散。在教育方面，该项目将支持一名来自代表性不足群体的教授的研究计划，并对研究生和本科生进行关于流体动力学、物理海洋学、内波理论、实验方法论和数据分析的想法、概念和实践的培训。这项研究还将在高中和较低级别的外展活动以及较高级别的课程中得到强调。

PI: Crockett, JulieProposal Number: 1606040The concentration of salt in the ocean changes with depth. This fact generates waves within the water that are called internal waves. The breaking of these waves drives much of the mixing in the deep ocean, defining mixing rates of pollutants, greenhouse gases, ocean nutrients and maintaining a balanced temperature distribution. It has been estimated that 2.1 terawatts of mixing power is required to maintain critical ocean mixing. Over half of the necessary power is postulated to come from internal waves generated by tidal flow over rough topography. The waves propagate through interactions with other waves and with ocean currents, until they convert to smaller scale, breaking waves. The focus of this proposal is to use laboratory experiments to study this process of internal wave generation and to understand how internal waves are generated and propagated within the ocean system. Findings from this research could lead to the development of new large scale ocean models that are important for the prediction of aquatic life migration patterns, for the prediction of the dispersion of pollutants in the ocean (like the dispersion of the radioactive spill from the Fukushima accident) and for the prediction of weather and climate patterns.An unexpected contributor to internal wave generation is tides flowing over topography in regions where the stratification is too weak for internal waves to be generated directly above the topography, yet internal waves can be observed well above the topography in a region where the stratification has increased. These waves may contribute to the conversion of tidal energy from large to small scales, which has important environmental consequences for wave-breaking and resultant mixing. The work proposed here is an experimental and analytical effort to characterize a relatively unexplored method of internal wave generation - the generation of internal waves due to tidal flow over topography in regions of weak stratification (where internal waves are not predicted to propagate) which radiate into strong stratification regions with implications for characterizing the internal wave energy spectrum throughout the ocean. It is proposed to: 1) explore internal wave generation by both uniform and tidal flow over topography in a two-layer stratification profile using experimentation; 2) characterize the effect of variations in stratification profile on internal wave generation, where for all stratification profiles the topography is in a region of weak stratification, such that internal waves are not expected, with a stronger stratification above; and 3) create an analytical model of the energy propagation from the topography through the variable stratification including the region representing evanescent to propagating waves. The project will contribute to the development of experimental methodology and understanding of stratified flow dynamics which will inform large scale modeling systems, resulting in better wave generation, propagation, and dissipation estimates. On the educational side, the project will support a research program of a professor from an under-represented group and training of graduate and undergraduate students in the ideas, concepts and practice of fluid dynamics, physical oceanography, internal wave theory, experimental methodology, and data analysis. The research will also be highlighted in high school and lower-division outreach activities and in upper-division courses.