Dynamics of NAO

North Atlantic Oscillation (NAO), or Arctic Oscillation (AO) is one of the most well-known prominent recurrent planetary-scale flow pattern in the stormy northern winter atmospheric circulations. To understand the dynamic origin of the unique circulation pattern of NAO, we first propose a dynamic closure for describing the Synoptic Eddy and Low-frequency Flow (SELF) two-way interaction. Based on the closure, we further propose a linear dynamic theory for NAO. By organizing transient synoptic eddies in the storm track, the low frequency flow anomalies with the NAO-like structure are preferentially reinforced. This internal dynamic self-organization of NAO results from a spatial scale-dependent positive feedback of the two-way SELF interaction, which makes NAO a leading dynamic mode of linearized atmospheric dynamic systems with respect to the observed stormy northern winter atmospheric circulations. Furthermore, the feedbacks through the ocean-atmosphere interaction can further enhance its dominance in the climate variability of long timescales.