solar disk called filaments. Filaments are primarily found in the solar quiet region (quiescent filament), between active regions or surrounding them (intermediate filaments) and inside active regions (active-region filament) [@mac10]. Generally, active-region filaments are shorter, smaller, lower in height, and have shorter lifetimes than quiescent and intermediate filaments. Nevertheless, active-region filaments are more unstable and more likely to erupt [@par14]. As the filaments lose the equilibrium, they would erupt and eject the material into the high corona. Filament eruptions are often accompanied with other solar activities (such as solar flares, coronal mass ejections (CMEs), coronal jets, surges, and so on) [@jin04].

Recently, understanding of solar filaments is one of the hot topics in solar physics, which includes their distribution, magnetic structure, formation, and eruption. Filaments always lie above the magnetic polarity inversion lines (PILs) separating opposite polarities of the photospheric magnetic field, which are considered to support by the local magnetic fields (e.g. magnetic dips or twisted structures) against the gravity [@bab55; @mar98; @che14a]. Unfortunately, due to the limitation of magnetic field measurements at present, it is difficult to measure directly the local magnetic fields in the filament. Therefore, the magnetic structures of filaments are still under controversy. There are 