PSI and near-inertial oscillations

非线性内波相互作用速率存在不确定性，特别是在光谱的近惯性部分。该项目旨在了解参数次谐波不稳定性（PSI）在将能量从潮汐和风产生的大规模相干内重力波传递到海洋内波谱的近惯性峰值中的作用。假设是，PSI是一种快速而稳健的机制，用于驱动小垂直尺度的快速、近惯性振荡。这种能量从2 0到0附近的转移需要合适的环境（例如，PSI在共振纬度上最有效）。如果该假设成立，则PSI是海洋混合的前奏，调节PSI的地理和环境因子对海洋混合的空间分布和垂直通量也起着重要的控制作用。对上述假设的评估需要对PSI将能量从模式一内部重力波转移到近惯性峰值的速率进行新的定量估计。为了符合实际，这些估计必须考虑内潮波列车的效应和垂直模态。因此，该项目的目标是获得PSI在实际分层海洋中从低垂直模态波列中消耗能量的速率的分析估计。数值模拟将对这些结果提供有用的检验，并使探索不稳定性的非线性发展成为可能。验证这一假设还需要评估地转涡旋在催化PSI和空间组织近惯性波中的作用。由于地转涡旋在空间和时间上的相干性，在海洋环境中产生了重要的不均匀性，内部重力波通过这些不均匀性传播。具体而言，有效惯性频率与实际惯性频率之差为地转平衡流相对涡度的一半。这种频移对近惯性峰值有强有力的影响，并可能扩大PSI所需的2.0 -共振。这些涉及近惯性谱峰、地转涡旋和PSI的问题可以在一个统一的理论框架下解决，提案的核心是发展、测试和应用该理论。更广泛的影响：海洋混合率不能以单一的普遍扩散率为特征，因此必须了解空间、时间和环境因素如何影响近惯性峰值的能量供应。需要更好地表示涡流通量，以便海洋学家能够可靠地模拟或诊断海洋在气候、海洋碳循环、向光能区提供营养物质以及有意在深水中处理碳和其他工业废物方面的作用。了解潮汐、内部重力波和地形相互作用在建立这些涡流通量中的作用是这个项目的目标。此外，研究生将接受物理海洋学理论和数值模拟方面的培训。

There is uncertainty about nonlinear internal wave interaction rates, particularly in the near-inertial part of the spectrum. This project is directed at understanding the role of parametric sub-harmonic instability (PSI) in transferring energy from large-scale, coherent internal gravity waves generated by tides and wind to the near-inertial peak of the oceanic internal wave spectrum. The hypothesis is that PSI is a rapid and robust mechanism for driving fast, near-inertial oscillations with small vertical scale. This transfer of energy from 2 f0 to the neighborhood of f0 requires the right circumstances (e.g., PSI is most effective at resonant latitudes). If the hypothesis is true, then PSI is a prelude to ocean mixing and the geographic and environmental factors modulating PSI also play an important role in controlling the spatial distribution of mixing and vertical fluxes in the ocean.The assessment of the hypothesis above requires new, quantitative estimates of the rate at which PSI transfers energy from mode one internal gravity waves into the near-inertial peak. To be realistic, these estimates must take account of the-effect and the vertical mode one structure of internal tidal wave trains. Thus the goal fo the project is to obtain analytic estimates of the rate at which PSI drains energy from a low vertical mode wave train in a realistically stratified ocean. Numerical simulations will provide a useful check on these results and enable exploration the nonlinear development of the instability.Validation of the hypothesis also requires an assessment of the role of geostrophic eddies in catalyzing PSI and in spatially organizing near-inertial waves. Because of their spatial and temporal coherence, geostrophic eddies create important inhomogeneities in the oceanic environment through which internal gravity waves propagate. Specifically, the effective inertial frequency differs from the actual inertial frequency by half of the relative vorticity of the the geostrophically balanced flow. This frequency shift has a potent effect on the near-inertial peak and may broaden the 2 f0-resonance required for PSI. These issues involving the near-inertial spectral peak, geostrophic eddies and PSI can be addressed under a unified theoretical framework and the core of the proposal is to develop, test and apply this theory.Broader impacts: Ocean mixing rates cannot be characterized by a single universal diffusivity and thus it is essential to understand how spatial, temporal and environmental factors affect the supply of energy to the near-inertial peak. Better representation of eddy fluxes are required so that oceanographers can reliably model or diagnose the ocean's role in climate, the ocean carbon cycle, the nutrient supply to the euphotoic zone and the intentional deep-water disposal of carbonand other industrial waste products. Understanding the role of tides, internal gravity waves and topographic interactions in establishing these eddy fluxes is the target of this project. In addition, a graduate student will be trained in both theory and numerical modeling in physical oceanography.