This paper reports two event studies on characteristic pitch angle variations of inverted-V electrons observed by the Reimei satellite. At edges of the inverted-V structures, the electron pitch angles are collimated between 0• and 20• while the electric field of the potential distribution is commonly depicted perpendicular to the local magnetic field. As Reimei moved toward the center of the inverted-V regions, the electron pitch angles broadened up to ∼120• , and their energies rapidly increased and continuously changed to those of the energetic inverted-V component. At the higher latitudes of the inverted-V structure, diffuse electrons with the isotropic distribution were also observed. Estimations of the electron density and temperature indicate that the source region of the beam electrons is the topside ionosphere by comparison with those of the diffuse electrons and the energetic inverted-V electrons. For the auroral emissions, in the first event, some horizontal auroral motions were observed which may be accompanied by the horizontal drift motion of the whole structure of the parallel potential drop. This motion could supply electrons in the topside ionosphere into the potential structure, and then the beam electrons are continuously formed at the low altitudes. In the second event, on the other hand, at both edges of the auroral band, the auroral emissions did not expand while the beam electrons were observed. One of the probable reasons to produce the beam electrons is the inertial Alfvén waves although they are inconsistent with previous studies because the velocity dispersions were not observed.

No abstract

Abstract. We performed 100 fps stereoscopic imaging of aurora for the first time. Two identical sCMOS cameras equipped with narrow field-of-view lenses (15° by 15°) were directed at magnetic zenith with the north–south base distance of 8.1 km. Here we show the best example that a rapidly pulsating diffuse patch and a streaming discrete arc were observed at the same time with different parallaxes, and the emission altitudes were estimated as 85–95 km and > 100 km, respectively. The estimated emission altitudes are consistent with those estimated in previous studies, and it is suggested that high-speed stereoscopy is useful to directly measure the emission altitudes of various types of rapidly varying aurora. It is also found that variation of emission altitude is gradual (e.g., 10 km increase over 5 s) for pulsating patches and is fast (e.g., 10 km increase within 0.5 s) for streaming arcs.

Electromagnetic ion cyclotron (EMIC) waves, one of the possible origins of flickering aurora, have been thought to modulate the electron flux at a few thousand kilometers. In fact, flickering aurora with a frequency range of 3–15 Hz has often been identified by ground‐based optical observations and has been interpreted to be caused by O+‐band EMIC waves. However, extant research to date has not identified possible signatures of H+‐band EMIC waves due to technical limitations of ground‐based high‐speed imagers. The present study shows the first evidence that patchy flickering aurora could be modulated by H+‐band EMIC waves, based on the data obtained from imaging observations at 160 frames per second. The sporadic appearance of the flickering aurora in the frequency range of 50–80 Hz coexisted with typical flickering auroras of approximately 10 Hz. These results are consistent with the hypothesis that flickering auroras are generated by multi‐ion EMIC waves.