Mechanism of forming a solar double-deck filament

(ORDO NEWS) — Researchers led by Zhang Yan and Yan Xiaoli from the Yunnan Observatories (YNAO) of the Chinese Academy of Sciences have uncovered the formation mechanism of the solar two-tier filament (dense, narrow filament of cosmic matter, consisting of dust and gases).

The filaments embedded in the solar corona are 100 times colder and denser than coronal matter. Filaments that appear on the limb as bright features are called prominences, and those that appear on the disk as features darker than their background are called filaments.

Bunk filament means two filaments arranged vertically above a single line of polarity reversal. There are two possibilities for the magnetic configuration of the double-deck filament: One is that both the top and bottom strands are flow ropes, and the other is that the top strand is a flow rope and the bottom strand is a sheared arcade. Until now, the description of the process of formation of two-layer filaments has been controversial.

In this paper, the researchers used multiband data from the Solar Dynamics Observatory and Hα imaging data from the Global Oscillation Network Group to study the filament in the NOAA 12665 ​​active region from July 8 to 14, 2017.

They found that due to photospheric magnetic motion and magnetic reconnection, two small filaments joined together and formed a longer magnetic structure. Then the newly formed filament split into two branches and finally formed a two-tiered filament.

It was found that the rotation of the sunspot, internal reconnection, and the movement of a negative magnetic field lead to the separation of the filament into two branches and the final formation of a two-tier filament. Internal reconnection can speed up their separation.

The researchers used non-linear field extrapolation without forces to obtain the magnetic configuration of the filaments. The results showed that the top and bottom filaments are magnetic flux ropes.

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