In situ observations of multistage electron acceleration driven by magnetic reconnection

Abstract:

With observations of magnetic reconnection and the related bursty bulk flow (BBF) in the magnetotail by Time History of Events and Macroscale Interactions during Substorms (THEMIS) Mission, we investigate the process of the multistage acceleration of electrons in magnetotail reconnection events, which can be divided into 3 distinct stages: (1) Firstly, electrons are accelerated in the vicinity of the X-line where the electron temperature can be significantly raised while the energetic electron flux with the energy larger than tens of keV has no obvious enhancement. (2) Secondly, electrons suffer the non-adiabatic acceleration in the pileup region of magnetic reconnection, which results in the obvious enhancement of the energetic electron flux and the small increase of the electron temperature in the earthward flow. (3) At last, the energetic electron flux can be further raised in the BBFs due to adiabatic acceleration mechanisms. Our study indicates that low energy electrons can be accelerated to a high energy with a multistage process in magnetic reconnection events, which ranges from the vicinity of the X line to the BBFs.