Scale interactions in the equatorial ocean

该项目旨在了解赤道温跃层中小垂直尺度特征的形成，它们与其他尺度的相互作用，以及对赤道气流大尺度动力学的总体影响。调查是在风强迫流域尺度流动的背景下进行的。刺激来自对赤道太平洋温跃层中这种小垂直尺度特征的观测，以及最近理论和数值工作的发现。除了常见的纬向平均气流的正压/斜压不稳定外，赤道流也受到不稳定的影响，这种不稳定有利于几十米量级的垂直尺度，但具有相对较大的经向和纬向范围。赤道温跃层中小垂直尺度特征的一个表现是水团的交错存在。前人的工作表明，这些特征对盆地尺度动力学有重大影响。我们设计了一系列数值实验来阐明这些小的垂直尺度结构的性质以及它们与其他尺度的相互作用。利用日本地球模拟器的大量计算资源，我们能够将这项研究放在整个盆地动力学的背景下进行。智力上的优点：空间尺度上的异常丰富，加上赤道海洋的高度时间变异性，提出了一些有趣和重要的问题，涉及特征的尺度选择过程、经向与纬向一致性以及尺度之间的潜在相互作用。小尺度特征本身可以引起示踪物、动量和位涡的相当大的混合，影响其他模式的发展和大尺度状态。我们的研究涵盖了最近才开始研究的赤道动力学的各个方面。我们将利用关于赤道气流稳定性的新发现。结果将是更好地理解赤道动力学和系统中多尺度相互作用的影响。更广泛的影响：气候预测的稳健性取决于大气和海洋模型捕捉问题基本物理的有效性。海洋状态影响耦合系统的季节和年际变化。海洋状态本身对横向和垂直混合的形式和程度非常敏感。在这里，我们计划明确地模拟由赤道温跃层中的小的垂直尺度结构引起的混合以及它们对盆地尺度动力学的整体影响。小垂直尺度特征本身依赖于从季节内到年际时间尺度上的较大尺度流动。我们有一种耐人寻味的可能性，可以在广泛的空间和时间尺度上进行多尺度的相互作用。本研究将在一定程度上评估气候模型中需要考虑这些相互作用的哪些方面。一名研究生将受雇于该项目。学生将接受流体动力学、数值建模和观测分析方面的培训。

This project is directed at understanding the formation of small vertical scale features inthe equatorial thermocline, their interaction with other scales, and the overall impact on the larger scale dynamics of equatorial flows. The investigation is undertaken in the context of the wind forced basin scale flow. The stimulus comes from observations of such small vertical scale features in the thermocline of the equatorial Pacific and findings emerging from recent theoretical and numerical work. In addition to the familiar barotropic/baroclinic instabilities of the zonal mean flow, equatorial currents are also subject to instabilities that favor much smaller vertical scales of the order of tens of meters but with relatively large meridional and zonal extents. A manifestation of small vertical scale features in the equatorial thermocline is the presence of the interleavingof water masses. Previous work suggests that such features have a significant impact on the basin scale dynamics. We have devised a series of numerical experiments to elucidate the properties of these small vertical scale structures and their interaction with other scales. Making use of the considerable computational resource of the Japanese Earth Simulator we are able to put this study in the context of the basin wide dynamics.Intellectual Merit: The extraordinary richness in spatial scales coupled with the high temporal variability of the equatorial ocean raises a number of intriguing and important questions concerning the scale selection process of features, meridional versus zonal coherence, and the potential interaction between scales. The small scale features themselves can induce considerable mixing of tracers, momemtum and potential vorticity, affecting the development of other modes and the large scale state. Our investigation covers aspects of equatorial dynamics that have only recently started to be studied. We will capitalize on new findings on the stability of equatorial flows. The outcome will be an improved understanding of equatorial dynamics and the impact of multi scale interactions in the system.Broader Impacts: The robustness of climate predictions depends on the effectiveness of atmosphere and ocean models to capture the essential physics of the problem. The ocean state affects the seasonal and interannual variability of the coupled system. The ocean state is itself very sensitive to the form and level of lateral and vertical mixing. Here we plan to explicitly model the mixing induced by small vertical-scale structures in the equatorial thermocline and their overall impact on the basin-scale dynamics. The characteristics of the small vertical scale features are themselves dependent on the broader scale flow on intraseasonal through to interannual timescales. We have the intriguing possibility of multiple scale interactions on a broad range of space and time scales. The present study will go some way to assessing what aspects of these interactions need to be taken into account in climate models. A graduate student will be employed on the project. The student will receive training in fluid dynamics, numerical modeling and analysis of observations.