Analysis of Altitude Structure and Morphological Differences of Pulsating Aurora Using ALIS_4D

Pulsating aurora is a type of aurora generated by the precipitation of electrons into the ionosphere as a result of pitch‐angle scattering through wave–particle interactions with whistler‐mode chorus waves excited near the magnetic equatorial plane in the magnetosphere. This generation mechanism has been established by observations showing a one‐to‐one correspondence between the timing of chorus wave excitation observed by magnetospheric satellites and the luminosity modulation of pulsating aurora at the magnetic conjugate point (Nishimura et al., 2010), as well as by direct observations demonstrating changes in the electron pitch‐angle distribution associated with chorus wave excitation (Kasahara et al., 2018).

Pulsating aurora exhibits a variety of morphological features. Grono and Donovan (2020) classified pulsating aurora into Amorphous Pulsating Aurora (APA), characterized by indistinct structures; Patchy Pulsating Aurora (PPA), which maintains stable patchy structures while pulsating; and Patchy Aurora (PA), which has stable patchy structures with no pulsation, and statistically investigated their occurrence regions. Ito et al. (2024) analyzed an event in which the dominant morphology temporally transitioned from APA to PPA/PA by using simultaneous observations from all‐sky imagers, the Arase satellite, and the EISCAT radar. They interpreted that, when magnetospheric density ducts—regions where the electron density is higher or lower than the surrounding plasma—are present, chorus waves can propagate from the magnetic equator along magnetic field lines to higher‐latitude regions closer to the Earth. Such propagation leads to spatially localized wave–particle interactions, resulting in the visualization of PPA/PA with well‐defined boundaries. Furthermore, by applying an inversion technique to electron density altitude profiles measured by the EISCAT radar, they reported that the energy of precipitating electrons increases during the occurrence of PPA/PA. When the average energy of precipitating electrons becomes higher, the auroral emission altitude is expected to decrease.

In this study, we report observations of pulsating aurora over northern Sweden obtained with the ground‐based multi‐point camera network ALIS_4D and present an analysis of their altitude distributions for different types of pulsating aurora. Based on these results, we further discuss the relationship between the morphological differences of pulsating aurora and the generation and propagation processes of chorus waves.