CMG: Unstable Periodic Solutions for Models of Atmospheric Dynamics

CMG：大气动力学模型的不稳定周期解

• 批准号: 0530868
• 负责人: Grant Branstator
• 金额: $ 18.82万
• 依托单位: University Corporation For Atmospheric Res
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-09-15 至 2008-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0530868&HistoricalAwards=false
• 关键词: CMG; Unstable; Periodic; Solutions; Models

This project uses an unstable periodic orbit analysis, applied to simplified models of atmospheric dynamics, to investigate the nature of time-dependent atmospheric dynamics. The choice of technique is based on the idea that many recurrent circulation patterns exhibit coherent, organized behavior for some period of time. The investigation will determine whether such an analysis can provide insights into what patterns are likely to occur and why, shed light on the nature of transitions between different atmospheric states, and help identify what type of model states should be most amenable to long-range prediction. The approach will then be used to examine how such properties of the atmosphere react to changes in external forcing.The two models that will be investigated are a barotropic model and a two-level quasigeostrophic model. The first part of the project will involve experimenting with ways of successfully finding unstable periodic orbits in such models, building on studies of unstable periodic orbits that have been made in other fields. Once found, the unstable periodic orbits will be compared with the aperiodic life-cycles of prominent circulation patterns such as the Pacific-North American pattern and the North Atlantic Oscillation. The project will continue with an attempt to use an expansion in unstable periodic orbits to approximate the response operator that describes the sensitivity of the atmospheric model to small changes in external forcing. The results will be compared with the approximate response operator derived from the fluctuation-dissipation theorem. Lastly, the predictability of states close to points on the least unstable periodic orbits will be examined with the intent of determining whether such states have anomalous predictability.If successful, the work may help understand variations in predictability in long-range atmospheric forcing, and provide a better understanding of uncertainty in some types of long-range forecasts.

这个项目使用不稳定周期轨道分析，应用于简化的大气动力学模型，以研究依赖于时间的大气动力学的性质。技术的选择是基于这样一个想法，即许多循环模式在一段时间内表现出连贯的、有组织的行为。这项调查将确定这样的分析是否可以提供对可能发生什么模式以及为什么发生的洞察，阐明不同大气状态之间转换的性质，并帮助确定哪种类型的模型状态最适合进行长期预测。然后，该方法将被用来研究大气的这些性质如何对外力的变化做出反应。将被研究的两个模式是正压模式和两层准地转模式。该项目的第一部分将在其他领域对不稳定周期轨道的研究的基础上，试验在这类模型中成功找到不稳定周期轨道的方法。一旦发现，不稳定的周期轨道将与太平洋-北美模式和北大西洋涛动等突出环流模式的非周期生命周期进行比较。该项目将继续尝试使用不稳定周期轨道的展开来近似描述大气模型对外部强迫的微小变化的敏感性的响应算子。结果将与由涨落耗散定理导出的近似响应算符进行比较。最后，将考察最不稳定周期轨道上接近点的状态的可预报性，以确定这些状态是否具有反常可预报性。如果成功，这项工作可能有助于理解长期大气强迫中可预报性的变化，并提供对某些类型的长期预报的不确定性的更好理解。