Variations in energy, flux, and brightness of pulsating aurora measured at high time resolution

Abstract

Abstract. High-resolution multispectral optical and incoherent scatter radar data are used to study the variability of pulsating aurora. Two events have been analysed, and the data combined with electron transport and ion chemistry modelling provide estimates of the energy and energy flux during both the ON and OFF periods of the pulsations. Both the energy and energy flux are found to be reduced during each OFF period compared with the ON period, and the estimates indicate that it is the number flux of foremost higher-energy electrons that is reduced. The energies are found never to drop below a few kilo-electronvolts during the OFF periods for these events. The high-resolution optical data show the occurrence of dips in brightness below the diffuse background level immediately after the ON period has ended. Each dip lasts for about a second, with a reduction in brightness of up to 70 % before the intensity increases to a steady background level again. A different kind of variation is also detected in the OFF period emissions during the second event, where a slower decrease in the background diffuse emission is seen with its brightness minimum just before the ON period, for a series of pulsations. Since the dips in the emission level during OFF are dependent on the switching between ON and OFF, this could indicate a common mechanism for the precipitation during the ON and OFF phases. A statistical analysis of brightness rise, fall, and ON times for the pulsations is also performed. It is found that the pulsations are often asymmetric, with either a slower increase of brightness or a slower fall.

Diffuse and Pulsating Aurora

“…observed that pulsating patch intensity is not symmetric in time, but rather increases more slowly than it decreases. Similarly asymmetric intensity rise and fall times were measured by Dahlgren et al (2017), who reported an average of 1.6 and 1.4 s, respectively. Based on analysis of optical and radar data of individual patches, precipitation energy and energy flux were found to be 60% lower during off times mainly due to the reduction of high-energy particle flux.…”

Over‐Darkening of Pulsating Aurora

“…This characteristic shape of the time‐series is fairly identical to the over‐darkening signature reported by Dahlgren et al. (2017).…”

“…Dahlgren et al. (2017) indicated that the over‐darkening signature is observed not only after the ON phase but also before the ON phase. Since Dahlgren et al.…”

“…Dahlgren et al. (2017) also indicated that such an over‐reduction of luminosity can also happen immediately before the start of the ON phase. Similar observations of such “over‐darkening PsAs” were previously reported by Kataoka et al.…”

“…The most recent observations were made by Dahlgren et al. (2017) who showed, by using a narrow field‐of‐view (FOV) EMCCD (electron multiplying charge coupled device) camera, that the brightness reduces below the background diffuse level immediately after the end of ON phase (i.e., very beginning of the OFF phase). Dahlgren et al.…”