AR magnetic topology and evolution over a 29 h period. The top row shows the evolution of AR 11150 in the AIA 171 Å observations with the line-of-sight magnetic field from HMI overlaid on top. The white (black) contours represent the positive (negative) magnetic field of AR 11150. The bottom row shows representative magnetic field lines (black) taken from the simulation throughout the evolution. The red (blue) contours represent positive (negative) magnetic flux. The saturation of the magnetic field in both rows is set to  + /− 100 G.