Near-Surface Conversions of Semi-Diurnal Internal Tide Beam Energy

当重力驱动的潮汐在地形上流动时，它们扰乱了海洋的内部分层（例如，暖水层在冷水层之上），产生了内部振荡（内部潮汐），具有相对强大的洋流和较短的空间尺度。内部潮汐的能量在混合深海及其随后对温度、盐度和营养分布的影响方面发挥着重要作用，这些影响对海洋动力学和生物地球化学（包括气候-时间尺度变异）具有深远的影响。因此，内部潮汐的能量分布是一个相当重要的课题。这个项目的重点是阐明内部潮汐能量如何以及有多少到达深海。研究人员将进行一系列数值调查，以描述和量化当向上传播的半日内潮汐与海洋表面附近的可变分层相互作用并向下反射时发生的过程。首要的问题是“内部潮汐在凌日和反射过程中‘损失’了多少能量？”尽管上层海洋内部潮汐能量的这种损失很少受到注意，但它可能导致海洋混合可用能量的显著减少，而海洋混合对于维持深层分层以及为表层附近初级生产提供营养至关重要。由于这些模式对混合分布的敏感性，在海洋和气候数值模式中适当地表示这些过程仍然是一个深入研究的课题。一位研究生，Sherry Chou女士，她为这个项目的提案提供了很多材料，她将继续接受内波科学和数值模拟技术的培训，并完成她的论文。数值模拟的结果也将告诉我们如何最好地应用海洋仪器来研究未来复杂的内波过程。该项目的主要目标如下：(1)确定在不同环境条件下（如不同的小尺度和大尺度分层结构）内潮与上层海洋分层和自由表面相互作用时，从内潮到其他现象（如孤立波、次谐波、超谐波）的能量通量的范围；(2)在海洋仪器采样的时空限制下，从数值调查中探索如何最好地区分和量化在实际海洋中内部潮汐过境期间可能同时出现的不同现象。

As the gravitationally-forced tides flow over topography they disturb the ocean's internal stratification (e.g., layers of warm over cold water), creating internal oscillations (internal tides) with relatively strong currents and short spatial scales. The energy of the internal tides plays an important role in mixing the deep ocean with subsequent impacts on temperature, salinity and nutrient distributions that have far-reaching consequences for ocean dynamics and biogeochemistry, including climate-time-scale variability. The distribution of the energy in the internal tides is therefore a subject of considerable consequence. This project is focused on elucidating how, and how much, internal tide energy reaches the deep ocean. The investigators will undertake a set of numerical investigations to characterize and quantify the processes occurring when an upward-propagating, semi-diurnal, internal tide interacts with the variable stratification near the surface of the ocean and reflects back downward. The overarching question is "how much energy is 'lost' from the internal tide during its transits and reflection?"Even though this loss of internal tide energy in the upper ocean has received little attention, it may result in a significant reduction in the amount of energy available to ocean mixing, which is critical for maintaining the stratification at depth, as well as the supply of nutrients for primary production near the surface. Proper representation of such processes in oceanic and climate numerical models continues to be a subject of intense research due to the sensitivity of these models to mixing distributions. . A graduate student, Ms. Sherry Chou, who has provided much material for the proposal resulting in this project, will continue her training in internal wave science and numerical modeling techniques, and will complete her dissertation. The numerical modeling results will also inform how best to apply oceanographic instrumentation to study intricate internal wave processes in the future. The project's principal objectives are as follows: (1) To ascertain the range of the fluxes of energy from the internal tide into other phenomena (e.g., solitary waves; sub-harmonic waves; super-harmonic waves) as it interacts with the upper ocean stratification and free surface under different environmental conditions (such as different small-scale and large-scale stratification structures); and, (2) To explore from the numerical investigations how best to try to discriminate and quantify the different phenomena, which may all be present at once during the internal tide's transit through the real ocean, given the spatial and temporal sampling limitations of oceanographic instrumentation.