Panel a: time-evolution of the double-J shaped QSL footprints (same as in Fig. 1) from the eruption onset up to the end of the simulation. Panel b: grayscale rendering of the flux distribution in the photosphere, with black-white standing for B_z = ⟨ − 2.4; 3⟩. The polarity inversion line (PIL; B_z = 0) is shown in yellow in both panels. Similarly, the pink and cyan isoncontours stand for B_z = 1 and −1, respectively. The colored circles and labels F1–F8 indicate the footpoints in the negative polarity B_z <  0 of the field lines whose time-evolutions are plotted in Figs. 4, 5, and 6.