The Mechanism of Magnetic Flux Rope Rotation During Solar Eruption

TL;DR

This study uses a full MHD simulation to determine that external shear magnetic fields primarily drive the rotation of erupting magnetic flux ropes during solar eruptions, with internal Lorentz forces opposing this rotation.

Contribution

It provides the first detailed simulation-based analysis distinguishing external shear-field influence from internal Lorentz forces in flux rope rotation.

Findings

External shear-field dominates flux rope rotation.

Lorentz torque inside the flux rope opposes rotation.

Simulation confirms external torque as the main driver.

Abstract

Solar eruptions often show the rotation of filaments, which is a manifestation of the rotation of erupting magnetic flux rope (MFR). Such a rotation of MFR can be induced by either the torque exerted by a background shear-field component (which is an external cause) or the relaxation of the magnetic twist of the MFR (an internal cause). For a given chirality of the erupting field, both the external and internal drivers cause the same rotation direction. Therefore, it remains elusive from direct observations which mechanism yields the dominant contribution to the rotation. In this paper, we exploit a full MHD simulation of solar eruption by tether-cutting magnetic reconnection to study the mechanism of MFR rotation. In the simulation, the MFR's height-rotation profile suggests that the force by the external shear-field component is a dominant contributor to the rotation. Furthermore, the torque analysis confirms that it is also the only factor in driving the counterclockwise rotation. On the contrary, the Lorentz torque inside the MFR makes a negative effect on this counterclockwise rotation.