Non-linear force-free field modeling of a solar active region around the time of a major flare and coronal mass ejection

TL;DR

This study uses advanced nonlinear force-free field modeling on high-quality solar magnetic data to analyze the magnetic field evolution during a major solar flare and CME, revealing the role of emerging currents and flux ropes.

Contribution

It applies multiple NLFFF models to high-resolution data to investigate the magnetic field changes associated with a significant solar flare and CME, providing insights into current emergence and flux rope topology.

Findings

Electrical currents emerge with magnetic flux before the flare

Currents are carried in thin strands within the flux rope

Energy change of ~10^32 erg powers the flare and CME

Abstract

Solar flares and coronal mass ejections are associated with rapid changes in field connectivity and powered by the partial dissipation of electrical currents in the solar atmosphere. A critical unanswered question is whether the currents involved are induced by the motion of pre-existing atmospheric magnetic flux subject to surface plasma flows, or whether these currents are associated with the emergence of flux from within the solar convective zone. We address this problem by applying state-of-the-art nonlinear force-free field (NLFFF) modeling to the highest resolution and quality vector-magnetographic data observed by the recently launched Hinode satellite on NOAA Active Region 10930 around the time of a powerful X3.4 flare. We compute 14 NLFFF models with 4 different codes and a variety of boundary conditions. We find that the model fields differ markedly in geometry, energy content, and force-freeness. We discuss the relative merits of these models in a general critique of present abilities to model the coronal magnetic field based on surface vector field measurements. For our application in particular, we find a fair agreement of the best-fit model field with the observed coronal configuration, and argue (1) that strong electrical currents emerge together with magnetic flux preceding the flare, (2) that these currents are carried in an ensemble of thin strands, (3) that the global pattern of these currents and of field lines are compatible with a large-scale twisted flux rope topology, and (4) that the ~10^32 erg change in energy associated with the coronal electrical currents suffices to power the flare and its associated coronal mass ejection.