a) Fieldline topology at the vertical yz-midplane, showing the plasmoid(s) at the interface (at t = 108 min). The horizontal cut shows the B_z component of the magnetic field at the photosphere, and the purple-green colorscale shows density in the yz-midplane. The fieldlines are colored according to the values of B_y. b) Isosurface of V> 60 km s^-1 showing the t = 114 min jet. White fieldlines show the stretch of the envelope field by the ejection. Overplotted is the full magnetic vector colored by the B_z component of the field at z = 0.9 Mm.