Sketch illustrating the development of rings in accretion discs. The black and blue arrows represent the radial flow and the wind, respectively. The green patches correspond to density minima where the vertical field B_z and the magnetisation μ grow. In this representation, the poloidal field lines (// to the wind) do not bend in the midplane but cross the disc with some angle. This configuration is actually not intuitive but is encountered in various disc simulations around the midplane.