Snapshots comparing the evolution of the systems in the eruptive (bottom row) and non-eruptive (top row) cases with medium arcade strength (B_d = ± 7.5). The respectively (cyan, orange) field lines initially belong to the (arcade, emerging flux rope). The two-dimensional (2D) horizontal cut displays the distribution at z = 0 of the vertical component of the magnetic field, Bz with a gray-scale code. Only the volume above that boundary is considered in the present study.