Collaborative Proposal: Laboratory Studies of Stirring by Small-Scale Geostrophic Motions

知识价值：沿海和公海的示踪剂释放研究表明，1至10公里尺度上的横向扩散不能用剪切扩散或侧向侵入扩散来解释。在这些尺度上的弥散可能是由于小尺度地转运动或涡旋模式的搅拌。分析和数值模拟研究支持这一结论。然而，对内波破碎事件的地转调整产生的旋涡模态、它们对横向搅拌的影响以及它们的最终耗散的完整描述仍然缺乏。所提出的实验室实验的目的是研究由地转调整的横旋混合事件形成的涡旋模式的横向搅拌。，并更好地量化海洋中涡旋模式搅拌的重要性。这项工作的主要贡献将是测试在存在内波强迫和破碎时对涡旋模态搅拌的理论预测，并为通过海洋涡旋模态搅拌参数化水平弥散率提供基础。实验将使用罗德岛大学海洋学研究生院的旋转水箱设备进行。一个直径1米，深30厘米的均匀分层旋转槽将用于模拟海洋分层内部的条件。将使用两种方法来产生双周期混合事件：1)局部网格强迫湍流形式的机械搅拌，以及2)由1型内波的近共振强迫和波-波相互作用产生的内波和破波的准随机场，将能量散射到更高的模态。将使用粒子成像测速（PIV）、激光诱导荧光（LIF）和数字视频分析相结合的方法来研究涡旋模式的形成及其对被动荧光染料横向搅拌的影响。与以往的分析和数值研究相比，所提出的实验室研究的一个主要优点是，底波混合事件最终将由内波破碎而不是一些人为强加的混合方法驱动。提出的工作将广泛建立在研究人员和合作者的分析和数值研究的基础上，这些研究预测了由旋涡模式搅拌引起的横向分散的数量。然而，这些研究并没有明确地包括破碎的内波，而是模拟了它们在浮力通量方面的影响。本研究的一个主要重点将是在明确包括大尺度内波强迫和内波破碎引起的底波混合的情况下测试理论和数值预测。这将使我们能够评估大尺度内波的影响，通过内波破裂的横旋混合转化为势能，以及能量向垂直模态的转移。更广泛的影响：拟议的工作将有助于提供海洋中1-10公里尺度上垂直模态搅拌的定量描述。这些尺度上的弥散影响物理、生物和化学示踪剂的分布，对于理解全球海洋环流和热平衡尤其重要，因为这些尺度近似于最先进的全球海洋环流模式的网格尺度。该项目是罗德岛大学和马萨诸塞大学达特茅斯分校的合作项目。每年将资助一名全日制研究生和一名本科生暑期实习生，为期四年。我们将尝试从代表性不足的群体中挑选候选人来填补这些职位。实验室的实验也将用于演示内部波浪动力学的物理海洋学课程，由调查员讲授。

0351892/0351905Intellectual merit: Tracer release studies in the coastal and open ocean suggest that lateral dispersion on scales of 1 to 10 kilometer cannot be explained by shear dispersion or dispersion by lateral intrusions. Dispersion on these scales may be due to stirring by small-scale geostrophic motions, or vortical modes. Analytical and numerical modeling studies support this conclusion. However, a complete description of the generation of vortical modes via geostrophic adjustment of internal wave breaking events, their effect on lateral stirring, and their eventual dissipation is still lacking. The goal of the proposed laboratory experiments is to study lateral stirring by vortical modes formed by geostrophic adjustment of diapycnal mixing events., and to better quantify the importance of vortical mode stirring in the ocean. The main contributions of this work will be to test theoretical predictions for vortical mode stirring when internal wave forcing and breaking are present, and to provide a basis for parameterizing horizontal dispersion rates by vortical mode stirring in the ocean. Experiments will be conducted using the University of Rhode Island's Graduate School of Oceanography rotating tank facility. A 1 meter diameter, 30 centimeter deep uniformly stratified rotating tank will be used to model conditions in the ocean's stratified interior. Two methods will be used to generate diapycnal mixing events: 1) mechanical stirring in the form of localized grid-forced turbulence, and 2) a quasi-random field of internal waves and wave breaking generated by near resonant forcing of a mode-1 internal wave, and wave-wave interactions to scatter energy into higher modes. The formation of vortical modes and their effects on lateral stirring of a passive fluorescent dye will be examined using a combination of Particle Imaging Velocimetry (PIV), Laser Induced Fluorescence (LIF), and digital video analysis. A major advantage of the proposed laboratory studies over previous analytical and numerical studies is that diapycnal mixing events will ultimately be driven by internal wave breaking rather than some artificially imposed method of mixing. The proposed work will build extensively on analytical and numerical studies by the investigators and collaborators, which predict the amount of lateral dispersion caused by vortical mode stirring. However, these studies did not explicitly include breaking internal waves, but simulated their effects in terms of buoyancy flux. A major focus of this study will be to test theoretical and numerical predictions when large-scale internal wave forcing and diapycnal mixing by internal wave breaking are explicitly included. This will allow an assessment of the effects of large-scale internal waves, the conversion to potential energy through diapycnal mixing by internal wave breaking, and the transfer of energy into vortical modes.Broader impacts: The proposed work will help provide a quantitative description of vertical mode stirring on scales of 1-10 km in the ocean. Dispersion on these scales affects distributions of physical, biological, and chemical tracers, and is particularly important to understanding global ocean circulation and heat balances, since these scales are approximately the grid scale of state of the art global ocean circulation models. The project is a collaborative effort between the University of Rhode Island and the University of Massachusetts at Dartmouth. It will support one full time graduate student and one undergraduate summer intern per year for four years. We will attempt to fill these positions with candidates from underrepresented groups. The laboratory experiments will also be used to demonstrate internal wave dynamics for physical oceanography courses taught by the investigators.