Space-time trajectories of magnetic null points mapping the evolution of the magnetic field structure (left). The green dots represent the X-points, the red dots the O-points. Panels a)−d) show the global view on magnetic field lines and corresponding current densities (red-blue scale) in the x − y computational plane at four consecutive times: a) at t = 0, b) at t = 3000, c) at t = 5000, and d) at t = 8000.