Model electric fields, using a cylindrical (left) and spherical (right) model for the polarisation field. Panels (a) and (b) show the field in the x–y plane and (c) and (d) show the field in the x–y plane. The colour-coded quantity is the magnitude of the component of the field in the plane shown, and the arrows indicate the direction of that in-plane component. The polarisation field models differ between the panels, and the cylindrical model also follows Nilsson et al. (2018) in that it does not include an ambipolar electric field. The parameters used correspond to simulation run C.