Mixing regions, mixing barriers and a closure theory for baroclinic turbulence

混合区域、混合障碍和斜压湍流的闭合理论

• 批准号: NE/G003122/1
• 负责人: James Esler
• 金额: $ 32.73万
• 依托单位: University College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2009
• 资助国家: 英国
• 起止时间: 2009 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FG003122%2F1
• 关键词: Mixing; regions; mixing; barriers; closure

The flow of air in Earth's atmosphere and water through the oceans is known to be turbulent on a wide range of scales (from centimetres to thousands of kilometres). The proposal aims to increase our theoretical and practical understanding of the turbulence that exists on the largest of these scales, i.e. those that determine the emergence, development and chaotic evolution of extratropical weather systems (cyclones and anti-cyclones), and oceanic eddies. Understanding the relationship between atmospheric weather systems (and oceanic eddies) and the mean currents that steer them, and from which they draw their energy, is central to understanding the Earth's climate system. One of the most important processes by which weather systems in the atmosphere and eddies in the ocean extract energy from the mean currents is known as baroclinic instability. If a current is unstable to baroclinic instability, a wave-like disturbance will emerge and grow in amplitude. Eventually this wave will `break' (in an analogous fashion to water waves on a beach) and the flow will become turbulent. The focus of the present proposal is to understand better the resulting `baroclinic turbulence'. Due to the many factors influencing the Earth's atmospheres and oceans, and the relative sparsity of observations, ideas relating to baroclinic turbulence are usually tested by comparing them with the results of idealised numerical models of flows in which relatively `clean' examples of unstable baroclinic flows can be simulated. The idea is to understand the `pure' process of baroclinic turbulence as it appears in the model flows, in order that the basic physics can be understood in isolation from all of the extraneous processes that are present in nature. This is the approach taken in the present work. A theory for the behaviour of flows experiencing baroclinic turbulence has been previously postulated by the PI and has proved successful in some preliminary tests. The current proposal aims to extend and verify the theory for a range of more realistic flows, by comparing theoretical predictions with the outcome of numerical model simulations as described above. The motivation in taking a gradual approach to additional complexity is to understand where the theory might break down, and if it does so, how it might then be modified. A successful outcome will greatly increase theoretical understanding of how waves and mean flows interact in the atmospheres and oceans, and it is hoped will lead directly to closely related ideas for representing the effects of ocean eddies in ocean climate models (which are currently too coarse in scale to capture eddy effects).

众所周知，地球大气层中的气流和海洋中的水流在很大范围内（从几厘米到几千公里）都是湍流。该提案旨在增加我们对这些尺度中最大尺度上存在的湍流的理论和实践理解，即那些决定热带气旋外天气系统（气旋和反气旋）和海洋涡旋的出现、发展和混乱演变的湍流。了解大气天气系统（和海洋涡旋）与引导它们并从中汲取能量的平均气流之间的关系，是了解地球气候系统的核心。大气中的天气系统和海洋中的涡旋从平均海流中提取能量的最重要过程之一被称为斜压不稳定性。如果海流不稳定到斜压不稳定，则会出现波浪状扰动，并使其振幅增大。最终，这波将“破碎”（类似于海滩上的水波），水流将变得湍流。本建议的重点是更好地理解由此产生的“斜压惯性”。由于影响地球大气层和海洋的因素很多，而且观测资料相对稀少，通常通过将斜压湍流的概念与理想化的流动数值模型的结果进行比较来检验，在理想化的流动数值模型中，可以模拟相对“干净”的不稳定斜压流动的例子。这个想法是为了理解斜压湍流的“纯”过程，因为它出现在模型流中，以便基本的物理学可以从自然界中存在的所有无关的过程中孤立地理解。这就是本工作所采取的方法。PI先前已经提出了一个关于经历斜压湍流的气流行为的理论，并在一些初步试验中证明是成功的。目前的建议旨在通过将理论预测与上述数值模型模拟的结果进行比较，来扩展和验证一系列更现实的流动的理论。采用渐进的方法来增加复杂性的动机是了解理论可能在哪里崩溃，以及如果它崩溃了，如何进行修改。一个成功的结果将大大增加理论上的理解波和平均流如何在大气和海洋中相互作用，并希望将直接导致密切相关的想法，在海洋气候模型中表示海洋涡旋的影响（目前尺度太粗，无法捕捉涡旋效应）。

项目成果

Nonlinear Baroclinic Equilibration in the Presence of Ekman Friction

存在埃克曼摩擦时的非线性斜压平衡

• DOI: 10.1175/jpo-d-11-0112.1
• 发表时间: 2012
• 期刊: Journal of Physical Oceanography
• 影响因子: 3.5
• 作者: Esler J

Stratospheric Sudden Warmings as Self-Tuning Resonances. Part II: Vortex Displacement Events

平流层突然变暖作为自调谐共振。

• DOI: 10.1175/jas-d-11-08.1
• 发表时间: 2011
• 期刊: Journal of the Atmospheric Sciences
• 影响因子: 3.1
• 作者: Matthewman N

Nonlinear baroclinic equilibration at finite supercriticality

有限超临界下的非线性斜压平衡

• DOI: 10.1080/03091929.2011.637033
• 发表时间: 2012
• 期刊: Geophysical & Astrophysical Fluid Dynamics
• 影响因子: 1.3
• 作者: Esler J

Estimation of the local response to a forcing in a high dimensional system using the fluctuation-dissipation theorem

使用涨落耗散定理估计高维系统中强迫的局部响应

• DOI: 10.5194/npg-20-239-2013
• 发表时间: 2013
• 期刊: Nonlinear Processes in Geophysics
• 影响因子: 2.2
• 作者: Cooper F

Stratospheric Sudden Warmings as Self-Tuning Resonances. Part I: Vortex Splitting Events

• DOI: 10.1175/jas-d-11-07.1
• 发表时间: 2011-11
• 期刊: Journal of the Atmospheric Sciences
• 影响因子: 3.1
• 作者: -N.;J. Matthewman;G. J.;Esler