Radial propagation of magnetospheric substorm-injected energetic electrons observed using a BD-IES instrument and Van Allen Probes

In cases where substorm injections can be observed simultaneously by multiple spacecraft, they can help elucidate the potential mechanisms of particle transport and energization, of great importance to understanding and modeling the magnetosphere. In this paper, using data returned from the BeiDa-IES (BD-IES) instrument onboard a satellite in an inclined (55A degrees) geosynchronous orbit (IGSO), in combination with two geo-transfer orbiting (GTO) satellite Van Allen Probes (A and B), we analyze a substorm injection event that occurred on the 16th of October 2015. During this substorm injection, the IGSO onboard BD-IES was outbound, while both Van Allen Probe satellites (A and B) were inbound, a configuration of multiple trajectories that provides a unique opportunity to simultaneously investigate both the inward and outward radial propagation of substorm injection. Indicated by AE/AL indices, this substorm was closely related to an IMF/solar wind discontinuity that showed a sharp change in IMF Bz direction to the north. The innermost signature of this substorm injection was detected by Van Allen Probes A and B at L-3.7, while the outermost signature was observed by the onboard BD-IES instrument at L similar to 10. These data indicate that the substorm had a global, rather than just local, effect. Finally, we suggest that electric fields carried by fast-mode compressional waves around the substorm injection are the most likely candidate mechanism for the electron injection signatures observed in the inner- and outermost inner magnetosphere.