| Magnetic reconnection is the key mechanism of explosive energy release in solarterrestrial space.It converts magnetic field energy into kinetic energy or heat energy of particles by changing the topological structure of magnetic field.Magnetic reconnection exists in astrophysical environments,geospace environments,and laboratory plasma environments.Numerous studies have demonstrated that the Hall effect is a hallmark process in collisionless magnetic reconnection,and Hall fields and electron motions exhibit different patterns under asymmetric and guide field conditions.The near-Earth space environment provided a natural laboratory for the study of magnetic reconnection.At the same time,satellite programs such as the Cluster and the Magnetospheric Multiscale provide in-situ observations with a high temporal resolution for the study of magnetic reconnection.This allows the Hall effect to be substantially studied.In recent years,simulation results of asymmetric magnetic reconnection have shown the existence of hexapolar Hall magnetic field pattern under asymmetric and guide field conditions.With the development of reconnection,the pattern evolved from the quadrupolar Hall magnetic field.This means that the pattern of the Hall field and the electron movement changes as reconnection develops,rather than a steady pattern.In order to study the Hall effect under asymmetric and guide field conditions,we selected magnetic reconnection events which are different from traditional Hall modes,and analyzed Hall field and electron outflows in the local coordinate system in detail.In addition,we also study the asymmetry of the quadrupolar Hall magnetic field under different mixing intensity of particle.The results are as follows:1.Anomalous out-of-plane magnetic field disturbances which are different from the traditional Hall magnetic field are observed in magnetic reconnection at subsolar magnetopause.The simulation results of the hexapolar Hall magnetic field explain the abnormal magnetic field pattern,which provides observational evidence for the hexapolar Hall magnetic field pattern in magnetospheric magnetic reconnection.There is also a corresponding outflow of electrons around the abnormal magnetic field,which provides a physical explanation for it.2.Apparent electron outflows at the separatrix of the magnetosphere side are observed in the magnetic reconnection at dawnward magnetopause.With the electron outflows,an abnormal out-of-plane magnetic field disturbance appeared at the magnetosphere side.Moreover,the starting point of the electron outflows is at the peak of the new magnetic field on the magnetosphere side.This means the abnormal magnetic field disturbance is closely related to the electron outflows.3.The asymmetric quadrupolar Hall magnetic field tends to be symmetric with increasing mixing intensity.This study divides the evolution of asymmetric magnetic reconnection into early-middle-late stages.At the early stage,the Hall magnetic field remains highly asymmetric and the peak value of the Hall magnetic field is located at the neutral sheet.At the middle stage,the Hall magnetic field is asymmetrical,but the peak value of the Hall magnetic field still remains at the magnetosheath side due to the sharp decrease of plasma density asymmetry in the Hall effect region.At the late stage,the plasma density in the Hall effect region is close to symmetry with the continuous mixing of particles.Therefore,the Hall magnetic fields on the magnetosphere side and magnetosheath side are separated by the neutral sheet,without position deviation.The results of this paper show that during the development of reconnection,different patterns of the Hall effect can be observed due to different asymmetric and guide field conditions.These results provide a new understanding of the Hall effect of magnetic reconnection,which can provide new ideas for future research. |
