Electron Mixing and Isotropization in the Exhaust of Asymmetric Magnetic Reconnection With a Guide Field

We investigate an exhaust crossing of asymmetric guide field reconnection observed by Magnetospheric Multiscale (MMS) mission at Earth's dayside magnetopause. One MMS spacecraft (MMS 4) observes multicomponent electron distributions, including two counterstreaming electron beams, while the other three MMS spacecraft, with a separation of ∼30 km, record nearly isotropic electron distributions. As counterstreaming electrons are unstable for the electron two‐stream instability, our observations suggest that the electrostatic waves generated by the fast‐growing electron two‐stream instability can contribute to the rapid isotropization of electron distributions in the reconnection exhaust, indicating that wave‐particle interactions play an important role in electron dynamics. Key Points Rapid isotropization of electron distributions has been observed in the exhaust of asymmetric guide field reconnection by different MMS spacecraft The high‐frequency electrostatic waves generated by the electron two‐stream instability can contribute to this process This study indicates that wave‐particle interactions play an important role in electron dynamics in asymmetric guide field reconnection