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LOW ORDER MODELS OF STORM TRACK VARIABILITY

风暴路径变化的低阶模型

基本信息

批准号：
2280622
负责人：
金额：
--
依托单位：
University of Reading
依托单位国家：
英国
项目类别：
Studentship
财政年份：
2019
资助国家：
英国
起止时间：
2019 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=studentship-2280622
关键词：
LOW ORDER MODELS STORM TRACK

项目摘要

The storm tracks in the Earth's atmosphere are the main locus of midlatitude weather systems. Their geometric structure is determined by local surface boundary conditions interacting with the mean flow which leads to local variations in the growth rate of baroclinic instability. Baroclinic instability is the relevant hydrodynamic instability which gives rise to midlatitude weather systems; its growth time scales are set by the vertical shear of the mean wind.The observed storm track shows variability on a broad range of timescales. The power spectrum of modes of variability is wide with substantial slow variability. Given that baroclinic instability works on relatively fast timescales, of around 3-5 days, it is the non-linear properties of the storm tracks that produce the slow timescales of 10 days or more, up to climate time scales.The aim of this project is to better understand the underlying non-linear dynamics leading to slow variability. In fact, the response of the storm tracks to slow climatic forcings is one of the key unknowns in future climate predictions, and it is one of the aims of this project to understand better how the underlying nonlinear dynamics of the storm track would react to changing external forcings.The main paradigm of understanding non-linear scale interactions in the storm tracks revolves around the idea of wave-mean flow interaction. Recent work, building on a long line of relevant progress, has demonstrated how low-order predator-prey models appear to capture important properties of the slow wave-mean flow interactions. There is substantial, but circumstantial evidence to show that the variability of storm tracks is determined by low-order dynamical systems. The derivations of the underlying predator-prey models has been mostly heuristic up to now, and first-principles derivations from the Navier- Stokes equations in the past have not been able to incorporate current understanding of storm-track variability.The initial approach to our study of the low-order dynamics of the storm track will come from two different sides:Firstly, using what we have learned from observed predator-prey style behaviour in the storm tracks we will apply model reduction techniques to reduce the full hydrodynamic models to low order versions that include known important dynamical features of the storm track (such as downstream jet latitude shifts).Secondly, starting from the published predator-prey models, we will attempt to extend those systems in a geophysically relevant way to capture more complex (likely chaotic) dynamics. Candidates for such extensions are: interactions with the humidity field (ther- modynamically the key source of energy in the storm track), jet latitude (a "known unknown" in climate dynamics), interactions with imposed external forcings (periodic, seasonal forcings, or stochastic forcings), but there may be others.There are several additional avenues available around those two directions and following on from them for approximately the final year of the project. Such avenues include substantial data analysis (where novel phase-space projections have recently been used), and idealised modeling (such models exist and are widely used to address fundamental GFD problems, typically around jet stream formation and variability).

地球大气中的风暴轨迹是中纬度天气系统的主要轨迹。它们的几何结构取决于局部地表边界条件与平均气流的相互作用，从而导致斜压不稳定增长率的局部变化。斜压不稳定是引起中纬度天气系统的相关水动力不稳定；其生长时间尺度由平均风的垂直切变确定。观测到的风暴路径显示出在大范围的时间尺度上的变化。变异性模态的功率谱很宽，具有大量的慢变异性。考虑到斜压不稳定在相对较快的时间尺度上起作用，大约3-5天，正是风暴路径的非线性特性产生了10天或更长时间的缓慢时间尺度，直至气候时间尺度。这个项目的目的是为了更好地理解导致缓慢变化的潜在非线性动力学。事实上，风暴路径对缓慢气候强迫的反应是未来气候预测的关键未知因素之一，而更好地了解风暴路径的潜在非线性动力学如何对变化的外部强迫作出反应是这个项目的目标之一。理解风暴路径中非线性尺度相互作用的主要范式围绕着波-平均流相互作用的思想。最近的工作，建立在一长串相关进展的基础上，已经证明了低阶捕食者-猎物模型似乎捕捉到了慢波-平均流相互作用的重要特性。有大量但间接的证据表明，风暴路径的变异性是由低阶动力系统决定的。到目前为止，对潜在的捕食者-猎物模型的推导主要是启发式的，过去从纳维尔-斯托克斯方程中得出的第一性原理推导还不能结合当前对风暴路径变化的理解。我们研究风暴路径低阶动力学的最初方法将来自两个不同的方面：首先，利用我们从观察到的风暴路径中的捕食者-猎物式行为中学到的知识，我们将应用模型简化技术将完整的水动力学模型简化为低阶版本，其中包括风暴路径已知的重要动力学特征（如下游急流纬度变化）。其次，从已发表的捕食者-猎物模型开始，我们将尝试以地球物理学相关的方式扩展这些系统，以捕获更复杂（可能是混沌的）动力学。这种扩展的候选者有：与湿度场的相互作用（在动力上是风暴路径的关键能量来源），急流纬度（气候动力学中的“已知未知”），与强加的外部强迫（周期性、季节性强迫或随机强迫）的相互作用，但也可能有其他的。在项目的最后一年，围绕这两个方向还有一些额外的途径。这些途径包括大量的数据分析（其中最近使用了新的相空间投影）和理想化的建模（这种模型存在并广泛用于解决基本的GFD问题，通常是围绕急流的形成和变化）。