Magnetohydrodynamics model of an X-class flare in NOAA active region 12017 initiated with non-force-free extrapolation

We present a three-dimensional magnetohydrodynamic simulation of the NOAA active region 12017 to explore the onset of an X-class flare on 2014 March 29 at 17:48 UT. The simulation is initiated with a magnetic field constructed by non-force-free-field extrapolation of the photospheric magnetic field. Importantly, the initial field contains a three-dimensional magnetic null, a pair of magnetic flux ropes, and a set of sheared arcades overlying the flux ropes at the flare location. A set of magnetic field lines are also identified which connect the flaring location to a distant region affected by the flare. The simulated evolution documents the magnetic reconnections at the null, which can potentially explain the observed chromospheric brightenings during the flare. The sheared arcades also appear to rise and participate in reconnections at the null. Notably, under the favorable initial Lorentz force, the flux ropes lose their twist due to reconnection. The terminal geometry of the ropes and the arcades are similar to the observed post-flare loops. Interestingly, the connecting field lines appear to take part in reconnections at the null, which may lead to the brightenings at the distant region. Further, the free energy released during the evolution which turns out to be ≈ 6.8 × 10 31 ergs matches well with the observation.