(a) Synthetic B_z magnetograms for the model with a twist profile increasing with the radial coordinate of the torus (N_t, 0 = 0.5 and h = 1, defined in Eq. (2) at time steps 4, 19, 34, and 49). We use the same colour code and contours as in Fig. 3. The segments join the polarities barycentres (magenta line) and the core centres (black line). (b) Computed F_z (black), (blue), and (green) along the FR emergence. Dashed-vertical lines indicate the time step of each maximum flux with their respective colour. All fluxes are normalised to the maximum value of . (c) Evolution of the apparent tilt ϕ_a computed from the magnetic barycentres (black line) and of ϕ_c using CoFFE (see the inset). The red-shaded area corresponds to the values of ϕ_c computed for p within the interval [−1, 1] after the convergence criterion of the tilt angle is achieved. The associated movie is available online (fig6_a.avi).