Observation and modeling of the injection observed by THEMIS and LANL satellites during March 23rd, 2007 substorm event

During the first encounter of a substorm on March 23rd, 2007, THEMIS constellation observed energetic particle injections and dipolarizations in the pre-midnight sector during the onset. Clear injection and dipolarization signatures were observed by three probes (A, B and D) in the region around 11 Re and 21:00 local time. THEMIS C, which was leading in the constellation at 8.3 Re, also observed a good injection signature, but the dipolarization is not so clear. From the timing based on these observations, a westward expanding ion injection and dipolarization front is identified. In combination with the energetic particle observations from LANL geosynchronous satellites, the particle injection seemed to initiate between LANL-97A (21 LT) and 1989-046 (1 LT). Ion injection can only be observed west of the center, whereas electron injections can only be seen east of the center. This event provides us an excellent opportunity to examine the dipolarization and particle injection processes beyond geosynchronous orbit. We model this injection event by sending an earthward dipolarization-like pulse at 23 local time and record the injected ions and electrons associated this pulse at the various satellite locations. Most of the basic features of the injected particles during the main injection are reproduced and the timing among satellites is consistent with observations. It is suggested from the model that the center of this substorm injection was initiated around 23 local time and located beyond 19 Re.