Electron acceleration by dipolarization fronts and magnetic reconnection: A quantitative comparison

Suprathermal electrons with energy from tens of keV to hundreds of keV are frequently observed in the Earth's magnetotail. The generation of such electrons is typically attributed to either magnetic reconnection or dipolarization fronts (DFs). However, which one contributes more to the electron energization has been unclear so far. In this study, we quantitatively compare the electron acceleration by DFs and magnetic reconnection, using the Cluster data. We first analyze an event detected in the midtail and find that the electrons accelerated by DF are associated with magnetic reconnection. The electron energization at the DF is primary attributed to a local betatron process that has been successfully reproduced using an analytic model. In order to better understand this phenomenon, we examine another 17 similar events, and find that the DFs and magnetic reconnection contribute 11% 39% and 61% 89% to the flux enhancement, respectively. This study can help us better understand the electron acceleration in the magnetotail.