Electron Acceleration Rate at Dipolarization Fronts

Although it has been shown that betatron and Fermi mechanisms contribute to electron acceleration at the dipolarization front (DF), the relative efficiency of these acceleration processes is unclear. In this paper, we directly calculate the electron adiabatic acceleration rate (the instantaneous acceleration) at DFs by using the data from the Magnetospheric Multiscale mission. We find that betatron acceleration dominates at the DF. Although the Fermi acceleration rate is smaller than the betatron acceleration rate, it is effective on a larger spatial scale than betatron acceleration, which is localized at the DF proper. The acceleration by the parallel electric field is negligible because it is far below the measurement uncertainties. The dependence of these acceleration rates on the DF normal, magnetic field, and thickness of the DF are analyzed. Our results provide important information for understanding the electron acceleration in the Earth's magnetotail.