Spectral analysis of flickering aurora

Abstract

We present a case study of a flickering aurora event observed from Poker Flat, Alaska. The data were recorded using an Andor EMCCD narrow field of view (15° × 15°) imager. The images were recorded at 33.58 frames per second resulting in 256 × 256 pixel images. The specific event analyzed consists of a time series of images lasting approximately 30 seconds (1000 images) where flickering aurora was observed throughout the entire sequence. An asymmetry was found in the scale size of the patches, with the East–West direction being approximately twice as large as the North–South direction. The calculation of the spatiotemporal spectra reveals that the temporal frequencies of the luminosity variations occur throughout the well‐defined range of 5 Hz to 14 Hz, with a sharp increase in power around 5 Hz and the peak at approximately 10 Hz. These data are compared to the theoretically calculated dispersion relation for ion cyclotron waves and the observed wave power can be bounded by using a k∥ between 1 × 10−5 m−1 and 3 × 10−5 m−1 for an altitude of 3100 km. Observationally there is a lack of power at values of k⊥ larger than ∼2 × 10−3 m−1, suggesting the existence of a minimum spatial scale for flickering auroral patches of approximately the O+ ion gyroradius (∼1 km) at the interaction altitude.