Understanding the formation and eruption of sigmoidal structure through data-driven modeling of magnetic evolution in solar active region 13500

Abstract

We investigate the magnetic origin of the coronal mass ejection (CME) that occurred on November 28, 2023, at 19:50UT from active region (AR) 13500 located near the solar disk-center. The eruption was associated with an S-shaped sigmoidal structure formed by the inner AR polarities along a sheared polarity inversion line, while the outer polarities evolved through proper motions. During November 26-28, the AR exhibited a decrease in net magnetic flux while progressively injecting magnetic helicity and energy into the corona toward the eruption onset, highlighting the key role of helicity-injection in triggering eruptions. To simulate this magnetic evolution, we employed a data-driven magnetofrictional (MF) simulation starting 2.8 days prior to the eruption. The energy input for the model was constrained using the observed energy injection through an ad-hoc parameter. The initial potential-field configuration gradually evolved into a sheared-arcade and eventually developed into a twisted flux rope (FR) over the observed time-scale. Proxy emission maps based on electric currents show remarkable morphological agreement between the simulated and observed sigmoidal structure. The average FR-core twist increasingly builds-up leading the FR to initiate slow-rise motion of FR top from 50Mm until its eruption onset at 80Mm. Importantly, the ratio of current-carrying to total relative-helicity increased from 0.13 at FR formation to 0.30 at eruption, when the FR core entered the torus-unstable regime, suggesting an association between torus-instability and a threshold helicity ratio. These results demonstrate that data-driven MF simulations can successfully reproduce the evolving coronal magnetic configuration and may provide a robust tool for assessing the eruptive potential of ARs, particularly the helicity ratio.

Figures (11)

• Figure 1: Multi-observation scenario of the CME eruption from the AR 13500 on November 28, 2023. a) Full disk image of the sun in AIA 304 Å showing the AR location (yellow rectangular box), b) running difference image in AIA 193 Å, indicating the onset of the eruption from the AR 13500, c) LASCO/C2 difference image showing the halo-CME emerging from the sun, d) AIA 131 Å image of the AR 13500 present with an S-shape sigmoid, e) HMI magnetogram displaying the magnetic field distribution in the AR. For comparison, the trace of the sigmoid is overlaid (yellow dashed curve), f) GOES X-ray flux light curve referring to the M9.8 flare starting from 28T19:35 UT.
• Figure 2: Left: HMI vector magnetograms of the AR 13500 at different epochs of its evolution. Right: Derived velocity of the flux motions. Arrows referring to horizontal field are over plotted on the vertical component of the magnetic field. Prominent polarities are labeled in panel a). Notice that while N2 and P2 move antiparallel, N1 separates from N2 with a proper motion. Axis units are in pixels of 0.5 arcsec size.
• Figure 3: Time evolution of non-potential parameters in the AR 13500, a) Net magnetic flux showing a decreasing flux content as it evolves in time interacting magnetic polarities. GOES flux is also shown with y-axis scale on the right., b) Net vertical current in each polarity flux region, along with average twist parameter ($\alpha_{av}$), c) the helicity injection rate ($dH/dt$, Y-axis on left) and accumulated helicity $H(t)$ (red, Y-axis on right). As marked by vertical dotted line, the peak $dH/dt$ is co-temporal with the CME eruption and the M9.8 flare d) helicity flux normalized with the square of magnetic flux.
• Figure 4: Constraining the energy injection for MF simulations from vector field observations. Top: Computed Poynting flux ($dE/dt$) and its accumulated quantity from the observed magnetic field at the photospheric surface. Bottom: Accumulated poynting flux from the electric fields derived with $U=120$ m/s (blue) and $U=150$ m/s (red).
• Figure 5: The evolution of AR magnetic structure at different epochs of the simulation. first column: top view, second column: perspective view, third column: Total current in the vertical cross section placed across the sigmoid. Magnetic field lines are colored by their field strengths, and the background image is the normal magnetic field Bz at the bottom of the computational domain ($z = 0$). The simulation captures the formation of the twisted flux rope by 50th hour along the PIL and its slow rise motion later. Arrow points to twisted flux that is being formed and rises progressively.