Using multispectral optical observations to identify the acceleration mechanism responsible for flickering aurora

Abstract

We present an analysis of flickering (2–10 Hz) auroras observed with a state‐of‐the‐art multispectral imaging system, Auroral Structure and Kinetics, located in Tromsø, Norway. Short (1–2 s) periods of flickering aurora have been identified in which the frequency of the brightness oscillations decreases or increases smoothly over time. To the authors' knowledge this is the first detailed analysis of such “chirps” in flickering aurora or field‐aligned bursts. We have found that the electron precipitation energy is strongly anticorrelated with the flickering frequency during all identified chirps. This result is consistent with the theory that flickering aurora is caused by the resonance interaction between electromagnetic ion cyclotron waves and precipitating electrons and that the wave parallel phase velocity is the primary factor determining the electron acceleration produced by this mechanism. Other current theories known to the authors cannot completely explain our observations.