Characteristic snapshots of TMFM run of AR12473 (top) and AR11176 (bottom). Field line colouring is based on seed-point location, chosen for appropriate contrast. The B_z component of the magnetic field is plotted at the bottom boundary, with the conventional grey-scale colour scheme (positive polarity in white, negative polarity in black; the respective maximum and minimum colour values are at 0.3T and −0.3T).