a) Initial condition of a linear force-free field for α = −2.93 × 10^-8 m^-1 where dips in the field lines (thick black lines) are plotted to one PSH and viewed from above. The solid/dashed black contours denote positive/negative values of B_z at levels of ± 70, ± 50, ± 1 Gauss. Physical dimensions are given in Mm. In panels b) to d) a close up view of the area enclosed by the dotted box in the panel a) can be seen after 1000, 2000 and 3000, 60 s long time-steps after the bipole has been inserted.