In Situ Observations of Separatrices in a Strong-guide-field Reconnection at the Magnetopause

Abstract

The reconnection in nearly symmetric inflow boundary conditions with a strong guide field of three is detected at the magnetopause. The thin current sheet was well resolved by the Magnetospheric Multiscale mission, which revealed that there is a pair of low-density separatrices and a pair of higher-density separatrices. Electron flow is accelerated toward the X-line along the low-density side and ejected out along the higher-density side. All flows are super-Alfvénic, but the outflow velocity is much lower than the inflow velocity. It is further shown that the width of higher-density separatrices is about twice that of the low-density separatrices. Significant and opposite electric field activity is observed on both sides of the current sheet. Our observations show that the separatrix regions between the two sides of strong-guide-field reconnection are significantly different in structure and plasma properties, which in turn affect the acceleration and heating of electrons.