Electron properties in inverted-V structures and their vicinities based on Reimei observations

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. Key Points Beam electrons were observed at edges of inverted-V structures Beam electrons were observed whether the auroral motion was observed or not Estimations on the origin of beam electrons show it is the topside ionosphere