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

0351892/0351905智力优势：沿海和开阔海域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的扩散来解释。这些尺度上的扩散可能是由于小尺度地转运动或涡旋模式的搅动。分析和数值模拟研究支持这一结论。然而，对于内波破裂事件的地转调节涡旋模式的产生、它们对侧向搅动的影响以及它们最终的消散，目前还缺乏完整的描述。拟议的实验室实验的目的是研究由地转调节的昼夜混合事件所形成的涡模的横向搅动，并更好地量化涡模搅动在海洋中的重要性。这项工作的主要贡献将是检验当存在内波强迫和破裂时涡模搅动的理论预测，并为海洋涡模搅动的水平弥散率的参数化提供依据。实验将使用罗德岛大学海洋学研究生院的旋转水箱设施进行。一个直径1米、深30厘米的均匀分层旋转水箱将被用来模拟海洋分层内部的条件。两种方法将被用来产生昼夜混合事件：1)局域网格强迫湍流形式的机械搅拌，2)由1模内波的近共振强迫和波-波相互作用产生的内波和波破碎的准随机场，以将能量分散到更高的模。采用粒子成像测速(PIV)、激光诱导荧光(LIF)和数字视频分析相结合的方法，研究被动荧光染料涡旋模式的形成及其对侧向搅拌的影响。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势是，昼夜混合事件最终将由内波破裂驱动，而不是某种人为强加的混合方法。这项拟议的工作将广泛地建立在由研究人员和合作者进行的分析和数值研究的基础上，这些研究预测了涡流模式搅拌引起的横向弥散量。然而，这些研究没有明确地包括破裂内波，而是从浮力通量的角度模拟了它们的影响。这项研究的一个主要焦点将是检验理论和数值预报，当大尺度内波强迫和由内波破裂引起的昼夜混合被明确包括在内时。这将有助于评估大尺度内波的影响，通过内波破裂通过日向混合转换势能，以及将能量转移到涡旋模式。波及影响：拟议的工作将有助于对海洋1-10公里尺度上的垂直模式搅动提供定量描述。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量平衡尤为重要，因为这些尺度大约是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成果。它将在四年内每年支持一名全日制研究生和一名本科生暑期实习生。我们将尝试用代表人数不足的群体的候选人来填补这些职位。实验室实验还将用于演示研究人员讲授的物理海洋学课程的内波动力学。

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.