Variations of the 3-D coronal magnetic field associated with the X3.4-class solar flare event of AR 10930

TL;DR

This study investigates the 3-D coronal magnetic field variations associated with an X3.4-class solar flare in active region 10930, revealing magnetic connectivity breaking and energy redistribution linked to the flare's initiation.

Contribution

The paper introduces a nonlinear force-free field extrapolation method to analyze 3-D magnetic field changes during a solar flare, highlighting the role of magnetic connectivity breaking in flare initiation.

Findings

Magnetic connectivity with strong negative alpha and current density is broken after the flare.

Magnetic energy density redistributes, increasing in lower regions and decreasing higher up.

The breaking site of magnetic connectivity coincides with the flare's initial eruption location.

Abstract

The variations of the 3-D coronal magnetic fields associated with the X3.4-class flare of active region 10930 are studied in this paper. The coronal magnetic field data are reconstructed from the photospheric vector magnetograms obtained by the Hinode satellite and using the nonlinear force-free field extrapolation method developed in our previous work (He et al., 2011). The 3-D force-free factor $\alpha$, 3-D current density, and 3-D magnetic energy density are employed to analyze the coronal data. The distributions of $\alpha$ and current density reveal a prominent magnetic connectivity with strong negative $\alpha$ values and strong current density before the flare. This magnetic connectivity extends along the main polarity inversion line and is found to be totally broken after the flare. The distribution variation of magnetic energy density reveals the redistribution of magnetic energy before and after the flare. In the lower space of the modeling volume the increase of magnetic energy dominates, and in the higher space the decrease of energy dominates. The comparison with the flare onset imaging observation exhibits that the breaking site of the magnetic connectivity and site with the highest values of energy density increase coincide with the location of flare initial eruption. We conclude that a cramped positive $\alpha$ region appearing in the photosphere causes the breaking of the magnetic connectivity. A scenario for flare initial eruption is proposed in which the Lorentz force acting on the isolated electric current at the magnetic connectivity breaking site lifts the associated plasmas and causes the initial ejection.