Magnetic Field Re-configuration Associated With a Slow Rise Eruptive X1.2 Flare in NOAA Active Region 11944

Abstract

Using multi-wavelength observations, we analysed magnetic field variations associated with a gradual X1.2 flare that erupted on January 7, 2014 in active region (AR) NOAA 11944 located near the disk center. A fast coronal mass ejection (CME) was observed following the flare, which was noticeably deflected in the south-west direction. A chromospheric filament was observed at the eruption site prior to and after the flare. We used SDO/HMI data to perform non-linear force-free field extrapolation of coronal magnetic fields above the AR and to study the evolution of AR magnetic fields prior to the eruption. The extrapolated data allowed us to detect signatures of several magnetic flux ropes present at the eruption site several hours before the event. The eruption site was located under slanted sunspot fields with a varying decay index of 1.0-1.5. That might have caused the erupting fields to slide along this slanted magnetic boundary rather than vertically erupt, thus explaining the slow rise of the flare as well as the observed direction of the resulting CME. We employed sign-singularity tools to quantify the evolutionary changes in the model twist and observed current helicity data, and found rapid and coordinated variations of current systems in both data sets prior to the event as well as their rapid exhaustion after the event onset.

Evolution of coronal magnetic field parameters during X5.4 solar flare

“…The photospheric vector magnetic field used as a boundary condition for extrapolation was generated following the same procedure as (Yurchyshyn et al, 2022). Specifically, using the same cylindrical equal area (CEA) projection used to produce the hmi.sharp_cea_720s series data (Bobra et al, 2014), HMI magnetic field measurements rebinned to 1 Mm pixel scale were transformed to a local Cartesian coordinate system.…”

“…Specifically, using the same cylindrical equal area (CEA) projection used to produce the hmi.sharp_cea_720s series data (Bobra et al, 2014), HMI magnetic field measurements rebinned to 1 Mm pixel scale were transformed to a local Cartesian coordinate system. A reference point centered on the base of the Cartesian box is used in the transformation, ensuring that the base maps are projected onto their LoS counterparts with minimum distortion (Yurchyshyn et al, 2022). The center of the data cube-i.e., the Cartesian box-was set to the HARP center coordinates, and the size of the box was 400 × 200 × 200 for x, y, z pixels with z in the vertical.…”

“…To accomplish this, twist maps-like that of Liu et al (2016) and Yurchyshyn et al (2022)-were calculated at vertical planes across and along the densest area of the OR and flare brightening, as well as in an area of weak magnetic field for reference (see Figure 8). For this flare event the area aligned well with the PIL, implying the eruption occurred directly over the PIL as opposed to the sliding eruption seen by Yurchyshyn et al (2022). A highly twisted structure-likely a MFR-is evident in Figure 9 (shown by dark-blue areas of high twist) over the inversion line.…”

“…The coronal field was modeled using NLFFF extrapolation, and the analysis showed that total energy and helicity budgets of flare producing ARs-i.e., extensive quantities-are not discriminative regarding the eruptive potential; however, the energy ratio, helicity ratio, and normalized current-carrying helicity-i.e. intensive quantities-seem to be distinctly different for eruptive flares compared to confined flares; Yurchyshyn et al (2022) used Solar Dynamics Observatory (SDO) Helioseismic and Magnetic Imager (HMI) (Couvidat et al, 2016) magnetograms to perform NLFFF extrapolation of coronal magnetic field above NOAA AR 11944 in order to study the evolution of the AR's magnetic field prior to the eruption of a X1.2 solar flare. Signatures of magnetic flux ropes (MFR) were detected at the eruption site several hour before the start of the event.…”

“…The purpose of this study is to investigate the evolution of the modeled coronal magnetic field data for a X5.4 solar flare event that occurred on 7 March 2012. Specifically, seven magnetic field parameters are calculated from the coronal magnetic field modeled using the same extrapolation technique as Yurchyshyn et al (2022) for a time interval of 1 h before through 1 h after flare occurrence. The temporal evolution of the coronal magnetic field parameters leading up to and following the eruptive event was analyzed, with the ultimate intent of discerning any possible discriminating signatures or clear predictors of solar flare occurrence.…”