Magnetic and stagnation point selection. The gray contours (at v_z = 0) enclose the upflows. Top panel: snapshot from the 100 G simulation. Green contours are at a vertical field strength of 1 kG, the blue contours enclose the centering pixels of our magnetic structures. Bottom panel: a snapshot from the nonmagnetic simulation. Pixels (red) show the regions of flow convergence used as reference (− 1 / div v_h< 26 s).