Buildup and Release of Magnetic Twist during the X3.4 Solar Flare of December 13, 2006

TL;DR

This study investigates the 3D magnetic structure evolution of NOAA 10930 during the December 2006 X3.4 solar flare, revealing how magnetic twist buildup and release through reconnection triggered the flare.

Contribution

It provides detailed analysis of magnetic twist dynamics and reconnection processes in a major solar flare using nonlinear force-free field extrapolation.

Findings

Negatively twisted lines underwent dramatic reconnection during the flare.

Positively twisted lines were injected near the polarity inversion line.

Mixed twisted fields and strong currents near the PIL are key to flare onset.

Abstract

We analyze the temporal evolution of the three-dimensional (3D) magnetic structure of the flaring active region (AR) NOAA 10930 by using the nonlinear force-free fields extrapolated from the photospheric vector magnetic fields observed by the Solar Optical Telescope on board {\it Hinode}. This AR consisted mainly of two types of twisted magnetic field lines: One has a strong negative (left-handed) twist due to the counterclockwise motion of the positive sunspot and is rooted in the regions of both polarities in the sunspot at a considerable distance from the polarity inversion line (PIL). In the flare phase, dramatic magnetic reconnection occurs in those negatively twisted lines in which the absolute value of the twist is greater than a half-turn. The other type consists of both positively and negatively twisted field lines formed relatively close to the PIL between two sunspots. A strong CaII image began to brighten in this region of mixed polarity, in which the positively twisted field lines were found to be injected within one day across the pre-existing negatively twisted region, along which strong currents were embedded. Consequently, the central region near the PIL distributed with a mix of differently twisted field lines and the strong currents may play a prominent role in flare onset.