Features of separatrix regions in magnetic reconnection: Comparison of 2-D particle-in-cell simulations and Cluster observations

摘要

In collisionless magnetic reconnection, the in-plane Hall currents are carried mainly by the magnetized electrons. The in-plane Hall currents are directed toward the X line along the magnetic field lines just inside the separatrices and away from the X line along the separatrices. Such a current system leads to the quadrupole out-of-plane magnetic field with the peaks between the regions carrying the in-plane currents. Simultaneously, the electron flow toward the X line along the separatrices causes electron density depletions along the separatrices. In this paper, the features of separatrix regions in magnetic reconnection and the relations between the electron density depletions and the out-of-plane magnetic field are investigated with both two-dimensional particle-in-cell simulations and Cluster observations. We conclude that the electron density depletions are formed because of the magnetic mirror, and they are outside the peaks of the out-of-plane magnetic field. Such a theoretical prediction is confirmed by both simulations and observations.