Researchers from Yunnan Observatories, Chinese Academy of Sciences have published new research in The Astrophysical Journal Letters, revealing a novel mechanism of filament splitting and double-decker filament formation. The paper features Professor SHEN Yuandeng from Harbin Institute of Technology, Shenzhen, and Associate Researcher BI Yi from Yunnan Observatories as corresponding authors, with LIU Dongxu, a master's student at Yunnan Observatories, as first author.

Previous observational studies have suggested that in some filament eruption mechanisms, such as magnetic reconnection, the filament will split if the reconnection occurs inside it. In such cases, the split filament forms a transient double-decker filament during its rise and eruption, which is an important formation mechanism for double-decker filaments. This mechanism requires close temporal alignment between the filament's splitting and eruption features.

Unlike previously observed events, the team’s analysis of joint multi-platform observational data from SDO/AIA and STEREO/EUVI, has reported, for the first time, a filament splitting event caused by the component reconnection mechanism. The splitting of the filament began over an hour before the appearance of eruption features. This indicates that, unlike in many previously observed events, the filament splitting was not triggered by the same physical process that caused the filament eruption.

During this unique splitting process, numerous small vertical jets appeared within the filament. Their dynamic characteristics resemble the nanojets discovered in recent years in coronal loops, which are caused by component reconnection between magnetic field lines with a small angle of misalignment. This suggests that component reconnection can occur inside a braided filament flux rope, causing the multiple clusters of magnetic field lines that make up the filament to become more parallel after reconnection, leading to the splitting of the flux rope.

Notably, the study directly observed brightening filament threads with small-angle misalignments and the subsequent vertical small jets. This provides valuable direct observational evidence for the component reconnection mechanism within the filament.

The research establishes a significant link between the small-scale component reconnection mechanism and large-scale filament splitting and the formation of double-decker filaments. This finding not only reveals the potential of the component reconnection mechanism to influence large-scale coronal magnetic structures and thermodynamic characteristics, but also provides new evidence for its prevalence (and that of its derived microflares). These insights open up new perspectives for an in-depth exploration of the coronal heating problem.

This research was supported by the Natural Science Foundation of China, the Yunnan Revitalization Talent Support Program-Science & Technology Champion Project, the "Light of West China" Program of the Chinese Academy of Sciences, the Shenzhen Key Laboratory Launching Project, and the Specialized Research Fund for State Key Laboratory of Solar Activity and Space Weather.

Figure 1: the black dashed lines in panel (a) show the brightening threads within the filament that feature a small-angle misalignment. The panels (b)-(d) show the two subsequent small-scale vertical jets. The panel (e) shows the distance-time plot made along the jet. The panels (f)-(g) show the results of the DEM analysis for the small jet S9.

Contact:
LIU Dongxu
Yunnan Observatories, CAS
E-mail:liudongxu@ynao.ac.cn