Analyses of Large-scale Extratropical Climate Variability and Change

该项目考虑了北半球和南半球中高纬度地区的大气环流，这些地区被称为温带地区。该项目有两个组成部分，一个是加强对温带环流内部变异性的了解，另一个是研究热力强迫推动温带风暴路径的外部强迫南北移动及其相关涡流(部分通过与锋面天气系统有关的空气运动发生)的过程。对第一个分量的研究是在两种主要结构类型的背景下进行的，即温带气流中的大尺度变率：1)主导纬向平均动能的变化以及涡动和纬向平均动能之间的转换(通过涡动动量通量发生)；以及2)主导涡势能变化以及纬向平均和涡动势能之间的转换(通过涡热通量发生)的结构。在南半球(SH)，这将是第一个分量的研究重点，控制纬向平均动能变化的结构是众所周知的南环模(SAM)，它构成了急流和伴随的风暴路径的南北移动。第二部分的研究试图了解温带环流如何对各种外力作出反应，这些外力包括平流层臭氧消耗(“臭氧层空洞”)、北极积雪和海冰面积减少、温室气体增加和太阳辐射。这项研究利用简化的大气环流模式研究了控制急流及其伴随的风暴路径响应的基本动力学，该模型的指导假设是，响应的关键方面可以通过扩散框架来理解，在扩散框架中，热流和位涡的涡流通量以向下梯度的方式移动，以匹配它们各自平均梯度的变化。由于该项目中涉及的基本动力学对于理解和预测地球表面所经历的敏感天气和气候的重要性，这项工作具有更广泛的影响。此外，这项工作将支持和培训来自代表性不足群体的两名研究生，从而扩大对科学的参与，并促进这一研究领域的工作队伍的发展。

This project considers the atmospheric circulation in middle and high latitudes of the Northern and Southern Hemisphere, regions referred to as the extratropics. The project has two components, one of which is to improve understanding of the internal variability of the extratropical circulation, and the other is to examine the processes through which thermal forcing drives externally forced north-south shifts in the extratropical storm tracks and their associated eddy fluxes (which occur in part through the air movements associated with frontal weather systems). Research in the first component is based on the premise that large-scale variability in the extratropical flow arises in the context of two primary types of structures: 1) those that dominate the variance of zonal-mean kinetic energy and the conversion between eddy and zonal-mean kinetic energy (which occurs through eddy momentum fluxes); and 2) those that dominate the variance in eddy potential energy and the conversion between zonal-mean and eddy potential energy (which occurs through eddy heat fluxes). In the Southern Hemisphere (SH), which would be the focus of research in the first component, the structure that dominates variance of zonal-mean kinetic energy is the well-known Southern Annular Mode (SAM), which constitutes a north-south shift of the jet stream and accompanying storm track. Research in the second component seeks to understand how the extratropical circulation responds to a variety of external forcings including the depletion of stratospheric ozone (the "ozone hole"), reductions in Arctic snow cover and sea ice extent, increases in greenhouse gases, and solar irradiance. The research addresses the fundamental dynamics which govern the response of jet streams and their attendant storm tracks using simplified atmospheric circulation models, guided by the hypothesis that key aspects of the response can be understood through a diffusive framework in which eddy fluxes of heat and potential vorticity shift to match, in a down-gradient sense, the changes in their respective mean gradients.The work has broader impacts due to the importance of the fundamental dynamics addressed in the project for understanding and predicting the sensible weather and climate experienced at the Earth's surface. In addition, the work will support and train two graduate students from underrepresented groups, thereby broadening participation in the sciences and contributing to the development of the workforce in this research area.