Upper row: maps of B_z in the initial conditions of our simulations with superimposed magnetic field lines (green for z < 0 and magenta for z > 0), where we set x_c = 0.5 Mm and L_∥ = 0.5 Mm (left-hand column), x_c = 2.0 Mm and L_∥ = 0.5 Mm (central column), and x_c = 0.5 Mm and L_∥ = 2.0 Mm (right-hand column) on the plane z = 0. Two lower rows: some representative magnetic field lines projected onto the x − y plane and x − z planes. Magnetic field lines are coloured black and orange if they cross the z = 0 plane, and magenta and green if they do not.