Polar Ultraviolet Imager observations of solar wind‐driven ULF auroral pulsations

Abstract

Analysis of a sequence of auroral images acquired by the Polar Ultraviolet Imager (UVI) during a long‐duration (∼1.5 hr) solar wind dynamic pressure enhancement reveals auroral intensity variations in the Pc5 band. Power spectral analysis indicates that the “auroral pulsations” appeared in multiple frequency bands predominantly in the day sector and the dawn‐dusk flank of the oval, with the maximum wave power skewing toward the dawn sector. Ground‐based magnetometer recordings showed Pc5 micropulsations modulated with the auroral pulsations. The lower frequency (1–3 mHz) auroral pulsations were modulated with solar wind dynamic pressure pulses moving tailward, whereas the higher frequency (6–8 mHz) ones were not. We concluded that the lower frequency auroral pulsations were driven directly by the solar wind, whereas the higher frequency ones were associated with global compressional cavity mode. This study shows for the first time the snapshot of global Pc5 ultralow‐frequency (ULF) waves and demonstrates that global far‐ultraviolet (FUV) imaging such as Polar UVI provides a powerful ancillary tool for studying ULF waves on a global scale.