Wave activities in separatrix regions of magnetic reconnection

Abstract

Two‐dimensional particle‐in‐cell simulations have reproduced the waves consistent with those observed frequently in the separatrix regions of magnetic reconnection in the Earth's magnetotail. The key process generating the waves is intense parallel acceleration of the electrons due to an electrostatic potential hump formed in the inflow side of the separatrices. The intense electron beams trigger the electron two‐stream instability (ETSI) and the beam‐driven whistler instability (WI). The Buneman instability (BI) is also excited by moderate electron beams arising upstream the potential hump. The ETSI generates the Langmuir waves, while the BI gives lower hybrid waves. Both modes evolve the electrostatic solitary waves in the nonlinear phases. The ETSI traps the electrons in the parallel direction and forms a flat‐top distribution with high‐energy cutoff. On the other hand, the WI scatters the electrons in the perpendicular direction, producing isotropic distribution with nonthermal high‐energy tail.