Spatio-temporal evolution of the mean energy of the precipitating electron flux in poleward-propagating pulsating auroras

Pulsating auroras (PsAs) blink quasi-periodically, with durations ranging from a few seconds to tens of seconds. They have been classified into several categories based on their motion. These auroras are generated by precipitating electrons, which are believed to result from pitch-angle scattering by lower-band chorus (LBC) waves excited near the magnetic equatorial plane. However, the mechanisms behind the different motion patterns of PsAs remain unclear. In this study, we focused on PsAs that repeatedly propagate poleward. We performed a computed tomography analysis using auroral images from all-sky cameras installed at three ground-based stations to reconstruct the precipitating electron flux. The results show that as PsA patches propagated poleward, the mean electron energy decreased from approximately 37 ± 8 keV to 19 ± 7 keV. In contrast, the mean energy of stable, patchy auroras—those that neither propagated nor blinked at the origin of the poleward motion—remained steady at around 37 keV. These findings suggest that the magnetic latitude at which LBC waves can propagate along magnetic field lines decreases as the excitation region of the waves shifts outward to higher L -shells near the magnetic equator. Simultaneous observations by the Arase satellite and all-sky cameras further support this finding. They show that the amplitude of LBC waves decreased above ~ 15° magnetic latitude when the satellite's footprint passed through poleward-propagating PsAs. It has been proposed that LBC wave propagation to high magnetic latitudes requires a duct-like refractive index structure. Thus, our results imply that such duct structures form in stable patchy auroras but are unable to follow the outward motion of the wave excitation region near the equator.