Ghost-cell exchange at the south and north poles in spherical coordinates for same resolution level (a), restriction (b) and prolongation (c). For clarity, the pole is represented as an expanded black circumference to identify the cell faces touching it, although no there is no excised region. As in Fig. 5, colored lines denote (magnetic) fluxes on the boundary faces that are communicated. For prolongation, dashed lines denote boundaries that contain only tangential fluxes necessary for restriction and the total extent of fine blocks including ghost regions is marked by a gray line. For cylindrical coordinates, the ghost-cell exchange at the z pole happens as for the north pole.