| 29 Jan 2026
Mean Energy variation of Diffuse Aurora Observed with the ASIS Spectrograph
Abstract. We analyze more than 20,000 spectra of diffuse aurora recorded by the ASIS spectrograph over two winters, focusing on events classified as diffuse by an AI-based system, which includes pulsating auroras as a major subset. Electron characteristic energies were derived from calibrated red/blue emission ratios using a lookup-table approach based on forward modeling. To assess the systematic evolution of these energies with magnetic local time (MLT), we applied a Bayesian regression framework to the median of the mean-energy estimates, providing a robust characterization despite the large intrinsic variability of diffuse precipitation. The results reveal a clear hardening of the precipitation toward the dawn sector. Using the AE index as a proxy for geomagnetic activity, we further show that the MLT-dependent trend is influenced not only by the instantaneous AE level but also by the recent magnetospheric history, as revealed by time-lagged classifications. These findings indicate that diffuse auroral precipitation retains an imprint of preceding magnetospheric dynamics and are consistent with chorus-wave scattering modulated by evolving plasma-sheet conditions.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Annales Geophysicae.
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