Two 3D views of the NLFFF magnetic field extrapolations with the same selected magnetic field lines as in Fig. 1b. Field lines are colored according to their associated helicity flux density value computed from Eq. (4), red or blue for positive or negative values. The values are saturated at ±1.5 × 10⁸  Wb  s^-1. Arrows show the viewing angles relative to Fig. 1 (orange) and to the bottom panel (white).