Modeling substorm ion injection observed by the THEMIS and LANL spacecraft in the near-Earth magnetotail

Abstract

[1] In this paper, we studied a substorm ion injection event by using magnetohydrodynamic (MHD) and large-scale kinetic (LSK) simulations. On 23 March 2007 the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite constellation provided us with a unique opportunity to study a substorm injection in the region beyond geosynchronous orbit. On this date all five THEMIS spacecraft observed a substorm injection in the near-Earth magnetotail (X ∼ −7 RE). We traced the trajectories of millions of protons coming from the solar wind in the time-dependent magnetic and electric fields obtained from a global MHD simulation of this substorm. The results reproduced the main features of the injection observed by THEMIS and Los Alamos National Laboratory (LANL) spacecraft, including the timing and dispersion properties of energetic flux increases. It was found that there were primarily two energization regions where particles gained energy during the substorm. One is around the near-Earth X line (X∼ −20 RE), where particles were mostly accelerated nonadiabatically by strong electric fields (both inductive and potential). The others were several stretched or localized regions between X = −7 RE and X = −18 RE, where particles were accelerated in nonadiabatic motion under the potential electric field.