Evidence of the Hall Effect Providing the Core Field inside a Magnetic Flux Rope in an Antiparallel Magnetic Reconnection

The observations from the Magnetospheric Multiscale mission on 2015 November 12 showed the existence of tripolar Hall magnetic fields north of the X line in a quasi-antiparallel reconnection at the dayside of the magnetopause. The bipolar variation in the normal component of the magnetic field inside the middle polar region of the tripolar Hall fields indicated the presence of an ion-scale magnetic flux rope. The coexistence of Hall fields and a magnetic flux rope provides the first evidence that the Hall effect in quasi-antiparallel magnetic reconnection can generate the core field inside a magnetic flux rope. There is one dip in the core field of the observed magnetic flux rope. We interpret the core field and the dip with the Hall effect associated with sequential multiple-X-line reconnection. The results of this study shed light on the mechanism of the generation of the core field inside the magnetic flux rope.