The Formation of a Small-scale Filament after Flux Emergence on the Quiet Sun

TL;DR

This study documents the formation of a small-scale solar filament on the quiet Sun, highlighting the role of flux emergence, magnetic reconnection, and photospheric rotational motion in filament development.

Contribution

It reveals how twisted emerging magnetic fields and persistent rotational motion contribute to filament formation and magnetic twist relaxation.

Findings

Filament formed through flux emergence and magnetic reconnection.

Photospheric rotational motion persisted for over 10 hours.

Negative magnetic helicity was injected during filament formation.

Abstract

We present observations of the formation process of a small-scale filament on the quiet Sun during 5-6 February 2016 and investigate its formation cause. Initially, a small dipole emerged and its associated arch filament system was found to reconnect with overlying coronal fields accompanied by numerous EUV bright points. When bright points faded out, many elongated dark threads formed bridging the positive magnetic element of dipole and external negative network fields. Interestingly, an anti-clockwise photospheric rotational motion (PRM) set in within the positive endpoint region of newborn dark threads following the flux emergence and lasted for more than 10 hours. Under the drive of the PRM, these dispersive dark threads gradually aligned along the north-south direction and finally coalesced into an inverse S-shaped filament. Consistent with the dextral chirality of the filament, magnetic helicity calculations show that an amount of negative helicity was persistently injected from the rotational positive magnetic element and accumulated during the formation of the filament. These observations suggest that twisted emerging fields may lead to the formation of the filament via reconnection with pre-existing fields and release of its inner magnetic twist. The persistent PRM might trace a covert twist relaxation from below photosphere to the low corona.