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

Abstract

Context. Magnetic reconnection is commonly believed to be responsible for flare-like events and plasma ejections in the solar atmosphere, but the field-line reconfiguration observed in association with magnetic reconnection has rarely been observed before. Aims. We attempt to reconstruct the configuration of the magnetic field during a magnetic reconnection event, estimate the reconnection rate, and analyze the resulting X-ray burst and plasma ejection. Methods. We use the local-correlation-tracking (LCT) method to track the convergence of magnetic fields with opposite polarities using photospheric observations from SOT/Hinode. The magnetic field lines are then extrapolated from the tracked footpoint positions into the corona, and the changes in field-line connections are marked. We estimate the reconnection rate by calculating the convective electric field in the photosphere, which is normalized to the product of the plasma jet speed and the coronal magnetic field strength inside the inflow region. The observed X-ray burst and plasma ejection are analysed with data from XRT/Hinode and TRACE, respectively. Results. We find that in this reconnection event the two sets of approaching closed loops were reconfigured to a set of superimposed large-scale closed loops and another set of small-scale closed loops. Enhanced soft X-ray emission was seen to rapidly fill the reconnected loop after the micro-flare occurred at the reconnection site. Plasma was ejected from that site with a speed between 27 and 40 km s -1 . The reconnection rate is estimated to range between 0.03 and 0.09. Conclusions. Our work presents a study of the magnetic field reconfiguration owing to magnetic reconnection driven by flux convergence in the photosphere. This observation of the magnetic structure change is helpful for future diagnosis of magnetic reconnection. The results obtained for the reconnection rate, the X-ray emission burst, and the plasma ejection provides new observational evidence, and places constraints on future theoretical study of magnetic reconnection in the Sun.