The Formation and Eruption of A Sigmoidal Filament Driven by Rotating Network Magnetic Fields

TL;DR

This study observes how rotating network magnetic fields (RNFs) twist and energize small filaments into a sigmoidal structure, which eventually erupts, highlighting RNFs' role in filament formation and eruption mechanisms.

Contribution

It provides direct observational evidence linking RNFs to the formation and eruption of sigmoidal filaments on the Sun.

Findings

RNFs twist filaments by nearly 200 degrees within 140 minutes.

The sigmoidal filament's twist exceeds 4π before eruption.

Kink instability likely triggers the filament eruption.

Abstract

We present the formation and eruption of a sigmoidal filament driven by rotating network magnetic fields (RNFs) near the center of the solar disk, which was observed by the one-meter aperture New Vacuum Solar Telescope (NVST) at Fuxian Solar Observatory (FSO) on 2018 July 12. Counterclockwise RNFs twist two small-scale filaments at their northeastern foot-point region, giving a rotation of nearly 200 degree within about 140 minutes. The motion of the RNF has a tendency to accelerate at first and then decelerate obviously, as the average rotation speed increased from 10 to 150 ,and then slowed down to 50 . Coalescence then occurs between filaments F1 and F2. Meanwhile the fine structures in the southwestern region of the filament was involved in another interaction of coalescence. The subsequent EUV brightening due to plasma heating is observed in the two interaction regions. These interacting structures, including F1, F2 and the fine structures in the southwestern region, eventually evolve into a larger-scale sigmoidal filament twisted in the same direction as the RNFs gave. The twist of the sigmoidal filament has exceeded 4{\pi} and the filament erupted finally. The motion of the sigmoidal filament keeps uniform until a nearby jet collides, causing the filament to erupt faster. These results provide evidence that RNF plays an important role in the formation and eruption of the sigmoidal filament. The phenomena also suggests that the kink instability is the trigger mechanism for the filament eruption.