Recently, the Monthly Notices of the Royal Astronomical Society published the latest research work conducted by PH.D. candidate KANG Kaifeng and Prof. LIN Jun from Yunnan Observatories of the Chinese Academy of Sciences (CAS) and other collaborators. They successfully constructed a data-constrained, non-linear force-free field (NLFFF) configuration for a large-scale horse-shoe-like filament in a decaying and diffuse active region.

A solar filament (also known as prominence) is a magnetic structure that floats in the corona and includes partially ionized plasma, which is much cooler and denser than their coronal surroundings. However, the reason why the cool and dense filament can exist in the hot and tenuous corona is still an open question. Magnetic fields are considered to be central to maintaining filament existence in the coronal surroundings. Therefore, measuring the magnetic field of filaments to obtain their 3D magnetic structure is key to better understand their structure, evolution and eruption. Unfortunately, only on the photosphere can magnetic field be routinely measured. The magnetic field in the upper solar atmosphere is very difficult to measure directly. In the most cases, the 3D coronal magnetic field is constructed by extrapolating the measured photospheric magnetic field.

According to the strength of magnetic field, filaments can be classified as active region filaments (AF), quiescent filaments (QF) and intermediate filaments (IF). The traditional NLFFF extrapolation methods perform well in constructing magnetic structures of small-scale AF but fail in large-scale IF and QF. On the basis of the regularized Biot–Savart laws method, KANG Kaifeng et al. successfully constructed a data-constrained, NLFFF configuration for an IF. Their results indicate that three regions with magnetic structures of different topological connection exist around the filament. The kernel region nearest to the filament possesses the strongest magnetic field, the outermost region has the weakest field, and the field in the middle region has an intermediate strength. At the same time, they conclude that the barbs of the filament are a natural consequence of the deformation of the magnetic flux rope, and are not anchored to the photosphere.

Contact:
LIN Jun
Yunnan Observatories, CAS
Email: jlin@ynao.ac.cn