Evolution of nightside subauroral proton aurora caused by transient plasma sheet flows

Abstract

AbstractWhile nightside subauroral proton aurora shows rapid temporal variations, the cause of this variability has rarely been investigated. Using well‐coordinated observations by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) all‐sky imagers, THEMIS satellites in the equatorial magnetosphere, and the low‐altitude NOAA 17 satellite, we examined the rapid temporal evolution of subauroral proton aurora in the premidnight sector. An isolated proton aurora occurred soon after an auroral poleward boundary intensification that was followed by an auroral streamer reaching the equatorward boundary of the auroral oval. Three THEMIS satellites in the magnetotail detected flow bursts and one of the THEMIS satellites in the outer plasmasphere observed a ring current injection together with electromagnetic ion cyclotron wave intensifications. Proton auroral brightenings occurred multiple times throughout the storm main phase and a majority of those were correlated with auroral streamers reaching the auroral equatorward boundary. This sequence highlights the important role of transient flow bursts and particle injections for plasma transport into the inner magnetosphere and thus reflects a tail‐inner magnetospheric interaction process in which transient flow bursts play an important role in injecting ring current ions into the plasmasphere, causing rapid modulation of precipitation and the resultant subauroral proton aurora.