The solar filaments are composed of relatively cold and dense plasma suspended in the corona through a complex magnetic field system. It is generally believed that the filament mass comes from the chromosphere. However, it is unclear how the filament mass is transported to the corona and what is the magnetic field structure.
The shear and convergence motions of the polarities under the filament are often observed, which may suggest that magnetic reconnection plays a very important role in the formation of the filament. Magnetic reconnection is a physical process in which two sets of magnetic field lines in opposite directions approach each other and reconnect, accompanied by the rapid release of magnetic energy.
Researchers led by Dr. XUE Zhike from the Yunnan Observatories of the Chinese Academy of Sciences (CAS) studied the reconstruction process of a solar filament caused by magnetic emergence and magnetic reconnection on June 4, 2021, mainly using the high-resolution data obtained by the 1-meter New Vacuum Solar Telescope (NVST) at the Fuxian Solar Observatory, the Solar Dynamics Observatory (SDO) and the Interface Region Imaging Spectrograph (IRIS).
The results were published in The Astrophysical Journal on March 1.
"The right leg of the filament initially showed a spread-out structure, which was confirmed by the extrapolated 3D magnetic structure," said Dr. XUE. Many small positive and negative magnetic polarities and magnetic loops gradually emerged near the magnetic polarity of the filament's right footpoint. During this process, the right leg of the filament was then split into two parts, while its left leg still maintained a whole structure.
Meanwhile, the newly emerged magnetic loops gradually rose upwards between the splitting parts. A small-scale magnetic reconnection occurred between the newly emerged magnetic loop and the magnetic fields supporting the southeastern splitting part. The longer magnetic loops resulting from the reconnection merged with the magnetic fields of the other part of the split filament part, and thus reforming an entire filament.
"Our observational results reveal that magnetic emergence is responsible for splitting of the filament, while magnetic reconnection leads to the reconstruction of the filament," said Dr. XUE.
