Magnetogram used for the magnetic field extrapolation. The vertical dashed line at the longitude of 191° corresponds to the limit between the synoptic magnetograms from rotations CR2125 (left) and CR2126 (right). The quadrupolar structure mentioned in the text is marked by grey circles. The black star indicates the solar disk centre as seen from Earth at the time for which geometry S was reconstructed (2012 July 25, 03:06 UT). The loop geometries, the heliographic grid, and direction cross shown in Fig. 1 were reproduced for easier comparison.