Reconfiguration of the coronal magnetic field by means of reconnection driven by photospheric magnetic flux convergence

摘要

Context. Magnetic reconnection is commonly believed to beresponsible for flare-like events and plasma ejections in the solaratmosphere, but the field-line reconfiguration observed in associationwith magnetic reconnection has rarely been observed before. Aims. We attempt to reconstruct the configuration of themagnetic field during a magnetic reconnection event, estimate thereconnection rate, and analyze the resulting X-ray burst and plasmaejection. Methods. We use the local-correlation-tracking (LCT) method totrack the convergence of magnetic fields with opposite polarities usingphotospheric observations from SOT/Hinode. The magnetic field lines arethen extrapolated from the tracked footpoint positions into the corona,and the changes in field-line connections are marked. We estimate thereconnection rate by calculating the convective electric field in thephotosphere, which is normalized to the product of the plasma jet speedand the coronal magnetic field strength inside the inflow region. Theobserved X-ray burst and plasma ejection are analysed with data fromXRT/Hinode and TRACE, respectively. Results. We find that in this reconnection event the two sets ofapproaching closed loops were reconfigured to a set of superimposedlarge-scale closed loops and another set of small-scale closed loops.Enhanced soft X-ray emission was seen to rapidly fill the reconnectedloop after the micro-flare occurred at the reconnection site. Plasmawas ejected from that site with a speed between 27 and 40kms-1. The reconnection rate is estimated to range between 0.03 and 0.09. Conclusions. Our work presents a study of the magnetic fieldreconfiguration owing to magnetic reconnection driven by fluxconvergence in the photosphere. This observation of the magneticstructure change is helpful for future diagnosis of magneticreconnection. The results obtained for the reconnection rate, the X-rayemission burst, and the plasma ejection provides new observationalevidence, and places constraints on future theoretical study ofmagnetic reconnection in the Sun. Key words: Sun: flares - Sun: activity - magnetic fields - Sun: corona - Sun: photosphere