Further Study of Dynamics of Low-Frequency Variability of the Extratropical Atmospheric Circulation

通过几十年的研究，人们已经认识到大气低频流异常和天气涡旋活动之间的内部动力反馈在维持热带外大气低频变率方面起着至关重要的作用。然而，其基本机制尚未完全了解。在先前关于发展明确描述天气涡旋和低频气流相互作用动力学的动力学闭合的项目的基础上，该项目寻求继续采用这种方法，以调查超过月至季节时间尺度的大气环流异常的形成机制及其激发机制。具体来说，研究人员提出了一个天气涡引起的动力学不稳定性的正自反馈作为低频行星尺度变率的基本机制之一。通过理论分析、动力学模拟和诊断等一系列研究，利用模式输出和再分析数据集，本项目将进一步研究（i）天气涡旋引起的动力学不稳定的性质，（ii）这种不稳定在热带外气候模态和行星尺度气候流异常产生中的作用，（ii）它对中纬度海气动力耦合的影响，这将有助于我们进一步了解热带外气候变率及其可预报性。它将对气候科学的若干领域产生影响，包括中纬度风暴路径的变化、北极涛动/北大西洋涛动以及中纬度海洋-大气动力耦合。

Internal dynamic feedback between atmospheric low-frequency flow anomalies and synoptic-eddy activity has been recognized through decades of research as playing an essential role in maintaining the extratropical atmospheric low-frequency variability. However, the underlying mechanism is not fully understood. Building on the prior project on the development of a dynamical closure that explicitly describes the dynamics of the synoptic eddy and low-frequency flow (SELF) interaction, this project seeks to continue this approach to investigate the mechanisms for the formation of atmospheric circulation anomalies beyond month-to-seasonal timescales and their excitation mechanisms. Specifically, the investigators propose a synoptic-eddy induced dynamic instability related to the positive SELF-feedback as one of the basic mechanisms for low-frequency planetary-scale variability. Through a hierarchy of studies including theoretical analysis, dynamical modeling, and diagnostics using both model outputs and reanalysis data sets, this project will further study (i) the nature of the synoptic-eddy induced dynamic instability, (ii) the roles of this instability in the generation of the extratropical climatic modes and planetary-scale climatic flow anomalies, and (ii) its impact on middle latitude air-sea dynamical coupling.This study will aid in the advancement of our understanding of extratropical climate variability and its predictability. It will have impacts on several areas of climate science, including variability of the mid-latitude storm tracks, and Arctic oscillation/North Atlantic oscillation, and middle latitude ocean-atmosphere dynamical coupling.