Multi-event analysis of plasma and field variations in the source of Stable Auroral Red (SAR) arcs in the inner magnetosphere during non-storm time substorms

Abstract:

Stable auroral red (SAR) arc is an aurora with dominant 630.0-nm emission caused by low-energy electron heat flux or precipitation into the topside ionosphere from the inner magnetosphere. SAR arc is observed at subauroral latitudes equatorward of the auroral oval and often occurs during the recovery phase of magnetic storms and substorms [e.g., Rees and Roble, Rev. Geophys., 1975; Takagi et al., GRL, 2018]. Kozyra et al. [JGR, 1997] has noted that there were three possible mechanisms to generate these low-energy electrons. The first hypothesis is the Coulomb collision between plasmaspheric electrons and ring current ions [e.g., Cole, JGR, 1965; Kozyra et al., JGR, 1987]. The second hypothesis is that the Landau damping of electromagnetic ion cyclotron (EMIC) waves causes heated electrons, resulting in their pitch angle scattering and precipitation into the ionosphere [Cornwall et al., JGR, 1971]. The third is that the kinetic Alfven waves (KAWs) with the parallel electric field to the magnetic field accelerate plasmaspheric electrons into the ionosphere [Hasegawa and Mima, JGR, 1978]. Inaba et al. [submitted to JGR, 2020] has identified that EMIC waves or KAWs associated with the SAR arc were not observed in the source region of SAR arc and has concluded that the Coulomb collision was the most plausible mechanism to cause the SAR arc. In this presentation, we show three conjunction events of SAR arcs observed by all-sky imagers and inner magnetospheric satellites (Arase and Van Allen Probes) during non-storm time substorms on 4 November 2019, 17 January 2015, and 19 December 2012. EMIC waves and KAWs were not observed in the source magnetosphere on these three events. We are also evaluating the electron heating rate through the Coulomb collision using full-energy range ion data observed by the satellites. In the presentation, we will discuss the production mechanisms of these SAR arcs based on these detailed analyses.