Formation of Quiescent Prominence Magnetic Field by Supergranulations

TL;DR

This study uses 3D magnetofriction simulations to show that Coriolis-induced vortical motions in supergranules are essential for forming the magnetic flux ropes that support quiescent solar prominences.

Contribution

It demonstrates the critical role of Coriolis force in helicity injection and magnetic flux rope formation in prominence development, a novel insight in solar physics.

Findings

Coriolis force is essential for magnetic flux rope formation.

Helicity is transferred and accumulated along the polarity inversion line.

Simulation results align with observed prominence magnetic structures.

Abstract

To understand the formation of quiescent solar prominences, the origin of their magnetic field structures, i.e., magnetic flux ropes (MFRs), must be revealed. We use three-dimensional magnetofriction simulations in a spherical subdomain to investigate the role of typical supergranular motions in the long-term formation of a prominence magnetic field. Time-dependant horizontal supergranular motions with and without the effect of Coriolis force are simulated on the solar surface via Voronoi tessellation. The vortical motions by the Coriolis effect at boundaries of supergranules inject magnetic helicity into the corona. The helicity is transferred and accumulated along the polarity inversion line (PIL) as strongly sheared magnetic field via helicity condensation. The diverging motions of supergranules converge opposite magnetic polarities at the PIL and drive the magnetic reconnection between footpoints of the sheared magnetic arcades to form an MFR. The magnetic network, negative-helicity MFR in the northern hemisphere, and fragmented-to-continuous formation process of magnetic dip regions are in agreement with observations. Although diverging supergranulations, differential rotation, and meridional flows are included, the simulation without the Coriolis effect can not produce an MFR or sheared arcades to host a prominence. Therefore Coriolis force is a key factor for helicity injection and the formation of magnetic structures of quiescent solar prominences.