Relationship of the SAR Arc Dynamics to Substorm Injection Based on the Aurorae Observation. Magnetospheric Phenomena in the Plasmapause Vicinity

— Stable auroral red (SAR) arcs are a consequence of the interaction of energetic ions of the ring current with the plasmapause. The literature is dominated by the idea that stable auroral red arcs are observed during the recovery phase of magnetic storms. Our previous studies of the subauroral luminosity at the Yakutsk meridian showed that auroral red arcs appear and/or brighten during the substorm expansion phase. This work presents for the first time the results of simultaneous observations by all-sky imagers of aurorae dynamics at Zhigansk station (GMLat 62°, GMLon 196°) and the formation of red arc at subauroral Maimaga station (GMLat 58°, GMLon 202°). The event of February 15, 2018, with a minimum SYM-H = –20 nT, in which the substorm growth phase occurred after the IMF Bz turned southward, is considered. The expansion phase of this substorm began in the evening sector of 2000–2200 MLT with further extension of the auroral bulge in the MLT postmidnight hours, where a red arc brightening from the western horizon to the east near the diffuse aurora boundary was observed. At this time, there was also an eastward movement of the glow ledges at the polar edge of the red arc, rays (corona) appeared and luminosity pulsations were registered in the vicinity of the diffuse aurora boundary in the 557.7 nm emission. The SWARM-B satellite detected subauroral electron temperature peaks at latitudes of the auroral red arc near the meridian of observations during the growth and recovery phases of the substorm. We assume that the auroral red arc in this event mapped the dynamics of the overlap of the flux of energetic ions with the outer plasmasphere as a result of the expansion of the region of substorm injection and the electric drift of energetic ions in the eastern direction.