Sketch of the ribbon formation in a plane perpendicular to the orientation of the undisturbed interstellar magnetic field (IMF, black lines). An enhancement of interstellar density (an H-wave, green area) is propagating through the heliosphere that is depicted by the terminaton shock (TS) and the heliopause (HP). In the intersection region, which is indicated by the shaded areas and forms a ring-like structure in 3D, the production rate of ENAs is increased. If in the more distant intersection regions more ENAs of higher energy are produced because of the continued acceleration of protons along the trajectories in the inner heliosheath (two examples are given as the curved red arrows), the ribbon appears under a wider angle in higher energies (as indicated by the three thin dashed solar line-of-sights, for details see text).