The Rotation of Magnetic Flux Rope Formed during Solar Eruption

TL;DR

This paper presents a magnetohydrodynamic simulation showing that magnetic flux rope rotation during solar eruptions is driven by magnetic reconnection, with observed changes in twist and writhe differing from kink instability explanations.

Contribution

It offers an alternative mechanism for flux rope rotation involving magnetic reconnection, challenging the traditional kink instability model.

Findings

Simulation reproduces observed flux rope rotation and morphology.

Rotation correlates with changes in twist and writhe of the magnetic flux rope.

Rotation mechanism differs from kink instability, emphasizing reconnection processes.

Abstract

The eruptions of solar filaments often show rotational motion about their rising direction, but it remains elusive what mechanism governs such rotation and how the rotation is related to the initial morphology of the pre-eruptive filament (and co-spatial sigmoid), filament chirality, and magnetic helicity. The conventional view regarding the rotation as a result of a magnetic flux rope (MFR) under-going the ideal kink instability still has confusion in explaining these relationships. Here we proposed an alternative explanation for the rotation during eruptions, by analyzing a magnetohydrodynamic simulation in which magnetic reconnection initiates an eruption from a sheared arcade configuration and an MFR is formed during eruption through the reconnection. The simulation reproduces a reverse S-shaped MFR with dextral chirality, and the axis of this MFR rotates counterclockwise while rising, which compares favorably with a typical filament eruption observed from dual viewing angles. By calculating the twist and writhe numbers of the modeled MFR during its eruption, we found that accompanied with the rotation, the nonlocal writhe of the MFR's axis decreases while the twist of its surrounding field lines increases, and this is distinct from the kink instability, which converts magnetic twist into writhe of the MFR axis.