Time series of the formation of a plasmoid ejection. Contours of  ⟨ A_x ⟩ _x are shown together with a color-scale representation of  ⟨ B_x ⟩ _x; dark blue stands for negative and red for positive values. The contours of  ⟨ A_x ⟩ _x correspond to field lines of  ⟨ B ⟩ _x in the yz plane. The dotted horizontal lines show the location of the surface at z = 0.