Fundamental Understanding of Magnetic Reconnection via Spiral CT Scan. VI. Parallel Electric Field and Electron Acceleration

For the first time, we reveal the distribution of parallel electric fields and suprathermal electrons around a reconnection X-line by using the spiral CT scan technique, which is a novel technique analogous to that in the hospital. This X-line was detected by the Magnetospheric Multiscale (MMS) mission at the magnetopause and has been widely believed to host an antiparallel reconnection without guide fields. With the help of such an advanced technique, we find that (1) suprathermal electrons exist mainly near the X-point and in the magnetosphere-side inflow region, but are sparse in the magnetosheath-side inflow region and near the separatrix; (2) parallel electric fields are strong near the X-point and in the magnetosphere-side inflow region, but are weak in the magnetosheath-side inflow region; (3) near the separatrix, electric fields are dominantly perpendicular rather than parallel; (4) both the enhancement of suprathermal electrons and parallel electric fields near the X-point are within a scale of 10 km (0.1 d_i); (5) the distribution of suprathermal electrons is different from the distribution of electron temperature, meaning that suprathermal electrons and thermal electrons have different behaviors near the reconnection site; (6) however, the distributions of suprathermal electrons and parallel electric fields are quite similar, indicating that the parallel electric fields may be responsible for suprathermal electron acceleration during reconnection. These results greatly improve our understanding of the electron acceleration during magnetic reconnection.