Electron surfing acceleration at rippled reconnection fronts

Earth depolarization fronts play a very important role in particle acceleration. It was widely believed that the front has a smooth planar surface and particles are influenced by large-scale fields. Recent observations found that the front surface is not smooth as expected but rather rippled. Small-scale fields were suggested to be of primary importance. In this study, we investigate how particles are influenced by such rippled fronts using a particle tracing technique. We find that the electron acceleration rate increases considerably in the rippled surface scenario as opposed to a smooth front surface. The main acceleration mechanism is surfing acceleration, in which the rippled structure can confines electron at the surface of DF for a longer time and accelerates them.