Top: four gray-scale slit reconstructed images representing He i red core intensity, increasing with time from left to right. Superimposed are white arrows indicating the horizontal magnetic fields observed with TIP-II in the He i 10 830 Å multiplet after solving the 180° ambiguity. Especially in the top right panel the magnetic field lines are well aligned with the dark He i threads. Bottom: background images show photospheric vertical fields observed with TIP-II in the Si i 10 827 Å spectral line. The images are saturated at  ± 400 G to emphasize the PIL. The black and white arrows (depending on the background for a better contrast) represent the horizontal fields. The arrows are parallel to the polarity inversion line, which lies in the gray area between 15 and 20 arcsec on the x-axis and extends from the lower to the upper part of each panel.