Time sequence analysis of flickering auroras, 1. Application of Fourier analysis

Abstract

Using a technique that enables one to digitize the brightness of auroral displays from individual fields of a video signal, we have analyzed the frequency content of flickering aurora. Through the application of Fourier analysis to our data, we have found that flickering aurora contains a wide range of enhanced frequencies, although the dominant frequency enhancement generally occurs in the range 6–12 Hz. Each incidence of flickering that we observed was associated with increased radio wave absorption. Furthermore, we have found that flickering occurs in bright auroral surges, the occurrence of which is not limited to the ‘breakup’ phase of auroral substorms. Our results are interpreted in terms of a recently proposed theory of fluctuating double layers that accounts for a number of the observational features.

Spatial-temporal characteristics of flickering aurora as seen by high-speed EMCCD imaging observations

“…[4] Flickering aurora has been typically reported to have a temporal fluctuation in the frequency range from 5 to 15 Hz [Beach et al, 1968;Berkey et al, 1980;Kunitake and Oguti, 1984;Sakanoi and Fukunishi, 2004;Whiter et al, 2008]. This frequency range is consistent with the O + ion cyclotron frequency at altitudes of several thousand kilometers.…”

Spectral analysis of flickering aurora

“…The phenomena of flickering aurora are characterized by periodic variations of the auroral luminosity, occurring in small spots and patches, that are caused by rapid and periodic modulations of the electrons precipitating from the magnetosphere [ Beach et al , 1968; Berkey et al , 1980; Whiter et al , 2008]. The modulation typically occurs at around 5 Hz to 14 Hz [ Beach et al , 1968; Berkey et al , 1980; Gustavsson et al , 2008]. This frequency range corresponds roughly to the O + ion cyclotron frequency at 1 R E altitude.…”

Optical observations of flickering aurora and its spatiotemporal characteristics

“…Flickering aurora is sometimes observed in bright aurora and during auroral breakup events. The flickering is characterized by spots with horizontal size of a few kilometers that vary in intensity typically at 5–15 Hz [ Paulson and Shepherd , 1966; Beach et al , 1968; Berkey et al , 1980]. During the 1–2 s lifetime of such spots, they can appear to both drift and rotate with high apparent velocity [ Kunitake and Oguti , 1984].…”