Unsigned flux density as a function of height for the four connectivities. The solid lines correspond to the top-bottom and bottom-top connectivities, the dashed lines to inverse-U loops, and the dot-dashed line to U loops. The upper panel is for t = 16 min, soon after the initial transient phase. Already a substantial amount of inverse-U loop flux has been generated. The lower panel is for t = 142 min. The top-bottom and bottom-top connectivities use the same linestyle to reflect the B → (−B) symmetry of the MHD equations.