The MFR in the NLFFF model and the MHD simulation of magnetic field evolution. Top two panels: top and side views of the MFR, superimposed on the HMI photospheric B_z map taken at 17 UT. The red arrow indicates the location of the magnetic NP. Middle panels: simulated 3D magnetic field lines (with vertical cross sections of ∣J∣/∣B∣) at Alfvén time t = 0.0, 1.6, and 3.2. Bottom panels: the top views of simulated horizontal magnetic field strengths in the photospheric layer (at an altitude of ∼400 km) at t = 0.0, 1.6, and 3.2. The color bar values for B_z and ∣B_h∣ represent percentages relative to their maximum values.