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

斜压湍流中的相干结构：喷流、涡流及其对海洋环流的影响

• 批准号: NE/E013171/1
• 负责人: Andrew Thompson
• 金额: $ 27.13万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2007
• 资助国家: 英国
• 起止时间: 2007 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FE013171%2F1
• 关键词: Coherent; structures; baroclinic; turbulence; jets

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.

在海洋流的观测和数值模型中发现的盆地尺度喷流，木星大气中非常稳定的东西向气流带的卫星图像，以及描述高度结构化湍流地球物理流的高分辨率数值模型，都促进了对大气和海洋喷流研究的复兴。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，大规模的环境流动倾向于在被称为射流的结构中沿东西或带状方向排列。近年来的研究在了解射流形成和维持背后的机制方面取得了进展，但对这些射流如何影响更大尺度的环流模式的关注较少。这项研究的目的是为了更好地了解海洋喷流及其相关的垂直和纬度结构如何与海洋盆地尺度和南大洋的南极环极流（ACC）内的流动模式相互作用。射流通常被描述为运输的障碍，它限制了通过射流核心的热量、化学物质和浮游生物的交换。但实际上，喷流是一种复杂的特征，表现出水平和垂直的变化。研究发现，射流作为运输障碍的有效性随深度而变化，通常有急剧的过渡。决定这些过渡深度的动力学还没有得到很好的理解。海洋环流模式也倾向于呈现垂直结构。例如，在太平洋环流，这是一个有许多喷流环绕南极洲的区域，经向或南北方向，气流被靠近表面的风推向赤道，而在深处，流体被海洋涡流带到极地。最近对ACC经向环流的描述没有包括急流的特征，因此是不完整的。在三维模型的帮助下，产生一系列类似于ACC中发现的射流，一个重要的目标是了解热量如何以及在什么深度通过射流传输，以保持ACC的强流。海洋涡流与喷流密切相关。通过从喷流中提取能量，漩涡往往会在喷流核心形成，而且漩涡可以沿着喷流追踪很长一段距离。漩涡也被证明可以通过将这些特性困在核心中并在移动时携带它们来增强海洋中热量、化学物质和生物的运输。因此，涡旋的作用对于理解热量和其他示踪剂如何在喷流中移动至关重要。不幸的是，分析大气和海洋湍流射流的传统方法依赖于统计技术，无法准确捕捉单个涡流的行为。对三维模型的分析能够解析喷流内部的涡流特征，这将为了解局部热和示踪剂的通量如何影响海洋盆地中这些特性的大规模输送提供新的和重要的见解。这项研究的最终目标是提高我们对现实海洋流动的理解。该研究的一个目的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。一种修改是包括陡峭地形的影响，这与ACC的气流特别相关，那里的地形特征有能力引导喷气机穿越经线。最后，通过与海洋学界的接触，从这项研究中获得的关于喷射结构对运输特性的具体作用的资料将用于改进现实的海洋模型和海洋观测方案。

项目成果

Surface circulation at the tip of the Antarctic Peninsula from drifters

• DOI: 10.1175/2008jpo3995.1
• 发表时间: 2009
• 期刊: Journal of Physical Oceanography
• 影响因子: 3.5
• 作者: A. Thompson;K. Heywood;S. Thorpe;A. Renner;A. Trasviña

Jet Formation and Evolution in Baroclinic Turbulence with Simple Topography

• DOI: 10.1175/2009jpo4218.1
• 发表时间: 2010-02
• 期刊: Journal of Physical Oceanography
• 影响因子: 3.5
• 作者: A. Thompson