Data-driven MHD Simulation of the Formation and Initiation of a Large-scale Preflare Magnetic Flux Rope in AR 12371

Abstract

Solar eruptions are the most powerful drivers of space weather. To understand their cause and nature, it is crucial to know how the coronal magnetic field evolves before eruption. Here we study the formation process of a relatively large-scale magnetic flux rope (MFR) in active region NOAA 12371 that erupts with a major flare and coronal mass ejection on 2015 June 21. A data-driven numerical magnetohydrodynamic model is employed to simulate three-dimensional coronal magnetic field evolution of one-day duration before the eruption. Comparison between the observed features and our modeled magnetic field discloses how the pre-eruption MFR forms. Initially, the magnetic field lines were weakly twisted as being simple sheared arcades. Then a long MFR was formed along the polarity inversion line due to the complex photospheric motion, which is mainly shearing rather than twisting. The presence of the MFR is evidenced by a coherent set of magnetic field lines with twist number above unity. Below the MFR a current sheet is shown in the model, suggesting that tether-cutting reconnection plays a key role in the MFR formation. The MFR's flux grows as more and more field lines are twisted due to continuous injection of magnetic helicity by the photospheric motions. Meanwhile, the height of the MFR's axis increases monotonely from its formation. By an analysis of the decay index of its overlying field, we suggest that it is because the MFR runs into the torus instability regime and becomes unstable that finally triggers the eruption.

Data-driven modeling of solar coronal magnetic field evolution and eruptions

“…According to the authors’ experience, to simulate the evolution of a typical size AR (say, 300 Mm in all three directions) for a typical timescale of a few days with a grid resolution that matches the HMI data (720 km), an MHD model with isothermal simplification needs months of computing time even when parallelized with a medium number of CPUs (for example, 100 processors with a frequency of 3 GHz). To reduce the computing time, some modelers 44 , 151 , 152 chose to speed up the cadence of feeding the observed data into the model by tens of times. This is reasonable by taking advantage of the fact that the photospheric evolution speed (with a typical velocity of 0.1–1 km s −1 ) is slower than the coronal evolution speed (of a few Mm s −1 ) by about three orders of magnitude.…”

“…Jiang et al. 44 developed such an MHD model (the so-called driven ARE (DARE)-MHD model 44 , 151 , 152 ) and successfully simulated a flux emergence event of over 3 days that finally leads to an eruption (of an M-class flare with a CME) in the topology-complex AR NOAA 11283. The simulation is started with a potential field extrapolation from the vertical component of the magnetogram taken for the initial time; thus, one can see how the pre-flare magnetic free energy is accumulated continually from the very beginning, driven by the flux injection with a strong shearing motion.…”

“… 154 Similar simulations of the large-scale MFR formation and eruption have been carried out for CME initiation in AR NOAA 12371. 46 , 151

Figure 6 The initiation mechanism of an M-class flare and eruption as revealed by a data-driven full MHD simulation (A) Sampled field lines showing the basic topology at the flare onset. Shown at the bottom is a AIA 304-Å image taken near the flare peak time to show the flare ribbons.

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Buildup of the Magnetic Flux Ropes in Homologous Solar Eruptions

“…Figure 10a shows the time evolution of the height of each MFR. Here, we assume that the axis of an MFR is located at the twist-weighted centroid of a strong twist kernel (twist number > 1; see Figure 7) on the twist map, and we regard the height of the twist-weighted centroid as the height of each MFR (e.g., Jiang et al 2014;He et al 2020). The height presents an increasing trend before each of the last three eruptions (see the red dots in Figure 10a).…”

Radiative Magnetohydrodynamic Simulation of the Confined Eruption of a Magnetic Flux Rope: Magnetic Structure and Plasma Thermodynamics

“…Based on the observing wavelengths, a variety of observational manifestations have been proposed to be related to flux ropes, such as filaments/prominences (Mackay et al 2010;Ouyang et al 2017), cavities (Régnier et al 2011;Gibson 2015), hot channels (Zhang et al 2012;Cheng et al 2013), and sigmoids (Green et al 2007;McKenzie & Canfield 2008). Moreover, quite a few magnetohydrodynamic (MHD) simulations based on different codes (e.g., Kliem et al 2013;Inoue et al 2014;Xia et al 2014;Fan & Liu 2019;Guo et al 2019;He et al 2020), which try to explain the roles of flux ropes in solar eruptions and their manifestations in observations, have been performed. For example, the simulations by Amari et al (2000Amari et al ( , 2003 ascribed the initiation of two-ribbon flares and CMEs to twisted flux ropes, which are formed through flux emergence or convergence after photospheric shearing motions.…”