Sensitivity of the magnetic field structure to the rotation curve and disc flaring, illustrated with magnetic fields constructed using fiducial parameters and (C₁, C₂) = (4.6 μG, −1.6 μG). The strength of the azimuthal component of the magnetic field is colour coded, while arrows indicate the direction and strength of the poloidal magnetic field. Details of the disc models are indicated above each frame and the disc scale height is indicated with a dotted line on the left and a dashed line on the right. Strong differential rotation near the galactic centre leads to a strong magnetic field, especially in a flat disc. In a flared disc, which is thinner at small s, the field strength near the galactic centre is reduced but the outer region has a stronger field.