Investigating pre-eruptive magnetic properties at the footprints of erupting magnetic flux ropes

TL;DR

This study investigates the magnetic properties at the footpoints of erupting magnetic flux ropes to identify pre-eruptive signatures and understand their formation, using vector magnetogram data from solar eruptions between 2010 and 2015.

Contribution

It provides evidence linking non-neutralized electric currents and pre-eruptive dimmings at flux rope footpoints to the presence of pre-existing MFRs before eruptions.

Findings

Only 8 of 28 MFRs had significant non-neutralized currents.

Pre-eruptive dimmings correlated with non-neutralized currents.

Asymmetry observed in twist and current distribution at MFR footpoints.

Abstract

It is well established that solar eruptions are powered by free magnetic energy stored in current-carrying magnetic field in the corona. It has also been generally accepted that magnetic flux ropes (MFRs) are a critical component of many coronal mass ejections (CMEs). What remains controversial is whether MFRs are present well before the eruption. Our aim is to identify progenitors of MFRs, and investigate pre-eruptive magnetic properties associated with these progenitors. Here we analyze 28 MFRs erupting within 45 deg from the disk center from 2010 to 2015. All MFRs'feet are well identified by conjugate coronal dimmings. We then calculate magnetic properties at the feet of the MFRs, prior to their eruptions, using Helioseismic and Magnetic Imager (HMI) vector magnetograms. Our results show that only 8 erupting MFRs are associated with significant non-neutralized electric currents, 4 of which also exhibit pre-eruptive dimmings at the foot-prints. Twist and current distributions are asymmetric at the two feet of these MFRs. The presence of pre-eruption dimmings associated with non-neutralized currents suggests the pre-existing MFRs. Furthermore, evolution of conjugate dimmings and electric currents within the foot-prints can provide clues about the internal structure of MFRs and their formation mechanism.