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

0351892/0351905知识价值：对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横向侵入扩散来解释。这些尺度上的弥散可能是由于小尺度地转运动或涡旋模态的搅动。分析和数值模拟研究支持这一结论。 然而，一个完整的描述生成的涡旋模式通过地转调整的内波破碎事件，它们对横向搅拌的影响，以及它们的最终消散仍然缺乏。拟进行的实验室实验的目的是研究由地转调整的横涡混合事件形成的涡模引起的横向搅动。并更好地量化海洋中涡旋模式搅动的重要性。这项工作的主要贡献将是测试理论预测涡模式搅拌时，内波强迫和破碎，并提供一个基础，参数化水平分散率的涡模式搅拌在海洋中。实验将使用罗得岛大学海洋学研究生院的旋转罐设施进行。一个直径为1米，深30厘米的均匀分层旋转罐将用于模拟海洋分层内部的条件。将使用两种方法来产生横周期混合事件：1）局部网格强制湍流形式的机械搅拌，以及2）由模式1内波的近共振强制产生的内波和波破碎的准随机场，以及将能量散射到更高模式中的波-波相互作用。涡流模式的形成及其对被动荧光染料横向搅拌的影响将使用粒子成像测速（PIV），激光诱导荧光（LIF）和数字视频分析的组合进行检查。与以前的分析和数值研究相比，拟议的实验室研究的一个主要优点是，底鼓混合事件最终将由内波破碎驱动，而不是一些人为施加的混合方法。拟议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，这些研究预测了涡旋模式搅拌引起的横向分散量。然而，这些研究并没有明确包括破碎的内波，但模拟其影响的浮力通量。本研究的一个主要重点将是测试的理论和数值预测时，大规模的内波强迫和diapycnal混合的内波破碎明确包括在内。这将有助于评估大规模内波的影响，通过内波破碎的横辐混合转换为势能，以及将能量转换为涡旋模式。更广泛的影响：拟议的工作将有助于提供海洋中1-10公里尺度上垂直模式搅动的定量描述。在这些尺度上的分散影响物理、生物和化学示踪剂的分布，并且对于理解全球海洋环流和热平衡特别重要，因为这些尺度近似于最先进的全球海洋环流模型的网格尺度。该项目是罗得岛大学和位于达特茅斯的马萨诸塞州大学的合作项目。它将支持一个全日制研究生和一个本科生每年暑期实习四年。我们将努力用代表性不足群体的候选人填补这些职位。实验室实验还将用于演示内波动力学，供调查人员讲授物理海洋学课程。

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.