Extrapolated 3D magnetic field lines overplotted on the photosheric magnetogram. Blue lines show the small-scale magnetic flux tubes connected to the small bipole region indicated with the blue rectangle in Fig. 8. Green lines indicate the magnetic field lines that show a dip near their middle part. White lines indicate the overlying large-scale loop. White lines are closed lines, only part of the lines is shown here in order to highlight the small-scale flux tubes. See Sect. 5.2.