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.
As a key component of the climate system, our earth atmosphere has great internal variability and this internal variability is one of major sources for internal climatic variability. Understanding the underlying dynamics of this variability is important for both improving the skill in short-term climate predications from seasons ahead and assessing long-term climatic changes of either anthropogenicor natural origins. This project thus focuses on the internal dynamic feedback between relatively slowing varying atmospheric flow (so-called low-frequency flow) anomalies which are responsible for extended periods of weeks or months dry/wet and hot/cold spells and much fast changing flow (so-called synoptic-eddy activity) patterns which produce every day whether activities. With the NSF project support, we developed a new mathematic framework of for this kind complex interaction and new approaches to diagnose the characteristics of this interaction in the nature and in the simulations of comprehensive computer models of climate systems. This study added to the advancement of our understanding of extratropical climate variability and its predictability. It will have impacts on several sub-areas of climate sciences. The results of the project added a new instability theory for understanding slow varying atmospheric flow variability and thus the associated climate variability, contributed to understand the dynamics of El Nino and its interaction with some fast variability in the tropics. We also applied our methodology to study the a number of important specific climatic phenomena including, the North Atlantic Oscillation, El Nino, etc, and to investigate how this specific interaction may affect the arctic climatic responses to global warming.
