Vorticity map after 445 rotations in a r − z cross section through the strongest vortex (same plot as in Fig. 13 but the contrast has been enhanced to make more salient weak features. The horizontal line (black dashed) indicates the height where becomes positive. The colored lines (dark-blue, cyan and green) indicate the position of the baroclinic critical layers, as computed from Eq. (26) with a source at the center of the mid-plane vortex for m = 16, 24 and 32, respectively. The dashed-colored lines are other critical layer curves with different positions of the source.