PSS (left) and examples of ray trajectories (right) for the three regimes identified in Fig. 2: sub-, trans-, and super-inertial, respectively. Blue trajectories correspond to invariant tori (except for the second case, which corresponds to an island chain), green ones to island chains, and the red one to a chaotic zone. Lighter blue and green trajectories correspond to periodic orbits at the centre of the islands. Magenta lines are the limits of the domain of propagation. The imprints of the rays are shown on the PSS with colours corresponding to the rays.