Left and middle panel: time evolution of the potential energy variation term (dashed black line; dE_p/dt; Eq. (42)) and the different terms constituting the instantaneous time-variation of E_p (Eq. (42)): F_ϕ, Bz (blue line; Eq. (43)), and dE_p/dt|_ns (orange line; Eq. (44)). Left and middle panels: evolution for the convergence and dispersion central simulation, respectively. Right panel: time evolution of F_ϕ, Bz for the four simulations dispersion central (red line), dispersion peripheral (green line), stretching (yellow line), and convergence (blue line). The yellow band corresponds to the onset phase of the eruption.