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Description
Flickering aurora, which appears in association with bright auroral arcs, consists of patchy structures a few kilometers in horizontal size that rapidly blink on and off at a frequency of about 10 Hz. Although the generation process of this phenomenon is not yet fully understood, the close similarity between the flickering period and the frequency of O^+ -mode electromagnetic ion cyclotron (EMIC) waves in the auroral acceleration region (at altitudes of several thousand kilometers), together with the agreement between the inferred wave number from the patch size and dispersion relation of EMIC waves, strongly suggests that EMIC waves play an essential role. If EMIC waves are indeed responsible for producing flickering aurora, then observations of flickering aurora may in turn provide clues to the conditions required for generation of EMIC waves. For example, the excitation of EMIC waves may depend on the spatial structure of the acceleration electric field of background arcs, and the background magnetic field strength (and thus the altitude where EMIC waves accelerate electrons) can be inferred by interpreting the flickering period as the oxygen ion cyclotron frequency. To enable such diagnostic studies, it is crucial to observe flickering aurora over a wide field of view. However, previous observations have mainly used narrow-field cameras to resolve their fine structures. In this study, we present a case of flickering aurora observed with a diagonal fisheye lens at Poker Flat Research Range, Alaska, and discuss the parameters influencing the generation of EMIC waves based on both the relative position between the flickering aurora and the auroral arc and the spatiotemporal characteristics of the flickering period.
