A statistical study of electron acceleration behind the dipolarization fronts in the magnetotail

Abstract

Abstract We investigate the electron acceleration behind dipolarization fronts (DFs) in the magnetotail from −25 R E to −10 R E through the examination of the energetic electron energy flux (>30 keV) with the observations from Time History of Events and Macroscale Interactions during Substorms (THEMIS). Statistical results of 133 DF events are presented based on the data set from January to April of the years 2008 and 2009. As the DFs propagate earthward, the acceleration of energetic electrons behind the DFs is found to take place over several R E along the tail. The increase in energetic electron energy flux can reach 2–4 orders of magnitude. The dominant acceleration mechanisms are different in the midtail ( X GSM ≤ −15 R E ) and the near‐Earth region (−15 < X GSM ≤ −10 R E ). In the midtail, the majority of DF events show that the dominant electron acceleration mechanism is betatron acceleration. In the near‐Earth region, betatron acceleration is dominant in ~46% DF events while Fermi acceleration is dominant in ~39% DF events.