Authors: Arpita Roddanavar (New Jersey Institute of Technology), Satoshi Inoue (New Jersey Institute of Technology)

We conducted magnetohydrodynamic (MHD) simulations to understand the erupting process of the sigmoid in active region (AR) 11283 that produced an X2.1 flare on September 6, 2011. The pre-erupting three-dimensional (3D) coronal magnetic field was obtained from a non-linear force free field (NLFFF) extrapolation method, which reproduced the sigmoidal structure well as shown in observations. This NLFFF is inferred from photospheric magnetograms acquired by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) about 1.5 hours prior to the flare. Although the NLFFF provides the information of the 3D magnetic field, it is in a static state or close to a static state. Therefore, a 3D magnetic field that deviates from the NLFFF  is required to cause an eruption. First, we conducted a data-constrained MHD simulation using NLFFF as the initial condition under the fixed boundary condition to hold the photospheric magnetic field and imposed anomalous resistivity in strong current density region to make highly twisted field lines. Then, we changed the bottom boundary condition where the horizontal components move freely and consistently interact with the magnetic induction equation. 

As a result, MHD simulations showed that the sigmoid quickly reconnects with the large coronal magnetic loops, and the twist of the sigmoid is transferred to those large loops. The large coronal loops gradually rose, but eventually, they stopped rising. We will discuss the sigmoid eruption with/without reconnection between the sigmoid and the large coronal loops, and the reason why the eruption was archived in this active region.