Coherent structures in baroclinic turbulence: jets, eddies and their influence on ocean circulation

在洋流观测和数值模式中发现了盆地尺度的急流，卫星图像显示了木星大气中非常稳定的东西向流纬向带，以及描述了高度结构的湍流地球物理流动的高分辨率数值模式，所有这些都促使大气和海洋中的急流研究卷土重来。由于地球的曲率，地球自转对流体运动的影响随着纬度的变化而变化。因此，大规模的环境流动往往在东西方向或地带性方向上对齐，这种结构被称为喷流。最近的研究在了解急流形成和维持背后的机制方面取得了进展，但对这些急流如何影响大尺度环流模式的关注较少。拟议研究的目标是更好地了解洋流及其相关的垂直和纬度结构如何与洋盆尺度和南大洋南极绕极流内的流动模式相互作用。喷气式飞机通常被描述为运输障碍，限制了热量、化学品和浮游生物在喷气式飞机核心之间的交换。然而，在现实中，喷气式飞机是复杂的特征，既表现出水平变化，也表现出垂直变化。研究发现，射流作为运输障碍的有效性随着深度的不同而不同，往往伴随着急剧的过渡。决定这些转变深度的动力还没有被很好地理解。海洋环流模式也倾向于呈现垂直结构。例如，在ACC，这是一个有许多急流环绕南极洲、经向或北/南的地区，气流在表面附近的风的推动下向赤道方向流动，而在深处，流体被海洋涡流带向极地。对行政协调中心经向环流的最新描述不包括急流特征，因此是不完整的。在一个三维模型的帮助下，产生一系列与ACC中发现的喷流相似的喷流，一个重要的目标是了解热量如何以及在多深的地方穿过这些喷流，以便维持ACC的强劲流动。海洋漩涡与喷流密切相关。漩涡往往通过从喷流中提取能量在喷流核心形成，并且涡旋可以沿着喷流长距离跟踪。涡流还被证明可以增强海洋中的热量、化学物质和生物的传输，方法是将这些特性困在岩心中，并在它们移动时携带它们。因此，涡流的作用对于理解热量和其他示踪物如何在喷流中移动至关重要。不幸的是，分析大气和海洋中湍流射流的传统方法依赖于无法准确捕捉单个涡流行为的统计技术。对能够分辨喷流内部涡流特征的三维模型的分析将为当地热通量和示踪剂如何影响海洋盆地中这些特性的更大范围的传输提供新的和重要的见解。这项研究的最终目的是提高我们对现实海洋流动的理解。这项研究的一个目标是确定与理想流动中的射流相比，更复杂的流动如何改变垂直和水平射流结构。一项修改是包括陡峭地形的影响，这与ACC中的流动特别相关，那里的地形特征有能力驾驶喷气式飞机越过经度线。最后，通过与海洋学界的接触，从这项研究中获得的关于喷流结构对运输特性的具体作用的信息将用于改进现实的海洋模型和海洋观测方案。

The discovery of basin-scale jets in observations and numerical models of oceanic flows, satellite images of remarkably steady zonal bands of east-west flow on Jupiter's atmosphere and high resolution numerical models depicting highly structured turbulent geophysical flows have all contributed to a resurgence in the study of jets in the atmopshere and ocean. Because of the Earth's curvature, the effects of the Earth's rotation on fluid motion changes with latitude. Thus large-scale environmental flows tend to align in east-west, or zonal, directions in structures referred to as jets. Recent studies have made progress in understanding the mechanisms behind jet formation and jet maintenance, however, less attention has been paid to how these jets influence larger-scale circulation patterns. The goal of the proposed research is to better understand how oceanic jets, with their associated vertical and latitudinal structure, interact with flow patterns at the ocean basin scale and within the Antarctic Circumpolar Current (ACC) of the Southern Ocean. Jets are typically described as barriers to transport that limit the exchange of heat, chemicals and plankton across the core of the jet. In reality, though, jets are complex features that exhibit both horizontal and vertical variability. The effectiveness of jets as barriers to transport is found to vary with depth, often with sharp transitions. The dynamics that determine these transition depths are not well understood. Ocean circulation patterns also tend to exhibit vertical structure. For example, in the ACC, which is a region with a number of jets that encircle Antarctica, meridional, or north/south, flow is driven equatorward by winds near the surface, while at depth, fluid is carried poleward by ocean eddies. The most recent descriptions of the ACC's meridional circulation do not include jet features and are therefore incomplete. With the help of a three-dimensional model that produces a series of jets that are similar to those found in the ACC, an important objective is to understand how and at what depth heat is transported across the jets in order to maintain the ACC's strong flow. Ocean eddies are closely linked with jets. Eddies tend to form at jet cores by extracting energy from the jet, and eddies can track along jets for long distances. Eddies have also been shown to enhance the transport of heat, chemicals and biology in the ocean, by trapping these properties within the cores and carrying them along as they move. Thus, the role of eddies is crucial for understanding how heat and other tracers move across jets. Unfortunately, traditional methods of analyzing turbulent jets in the atmosphere and ocean have relied on statistical techniques that are unable to capture the behaviour of individual eddies accurately. Analysis of a three-dimensional model that is able to resolve eddy features within the jets will provide new and important insight into how local fluxes of heat and tracers influence the larger-scale transport of these properties in ocean basins. Ultimately the goal of this research is to improve our understanding of realistic oceanic flows. One objective of the research is to determine how more complicated flows changes the vertical and horizontal jet structure as compared to jets in idealised flows. One modification is to include the effects of steep topography, which is of particular relevance to flows in the ACC, where topographical features have the ability to steer jets across lines of longitude. Finally, through contact with the oceanography community, information gained from this research on the specific role of jet structures on transport properties will be used to improve realistic ocean models and ocean observation programmes.