Top and side views of the potential field extrapolations for the MDI magnetograms of the AR 11059 taken on 2010 April 2 at 09:35 UT a), b) and on 2010 April 3 at 07:59 UT c), d), superimposed on the Hα images. In the side view, the red-white color scale is the magnetic field intensity. Different colors indicate different field lines bundles. Same colors between figures a), b) and c), d) indicate field lines starting from the corresponding flux distribution (see text).