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tokens: qualitatively understood in terms of the geometry of the heliosphere (see Sect. 4.2 ). 3. Comparing the observation regions of HSTOF and Voyager 1 The flux J ENA of the ENA originating in the heliosheath can be approximately expressed as where J ion is the parent ion flux (protons for hydrogen ENA, He + for helium ENA) at the same energy as J ENA , σ cx, H , and σ cx, He are the cross sections for charge exchange between the parent ions and the neutral hydrogen or neutral helium background gas of density n H and n He , respectively, and L is the thickness of the source region along the line of sight (LOS). The values J ion and n H are averages over the distance along the LOS within the source region (the inner heliosheath). For the helium ENA, we omitted the additional contribution from double charge exchange between the He ++ and the neutral He background, which is on the order of 3% ( Swaczyna et al. 2017 ). The equation does not include the ENA losses on the way from the source, but in the energy range where most of the ENA observations are carried out (IBEX Hi, INCA, and HSTOF) these effects are relatively small (about 1% for HSTOF). Fig. 4. Solar wind flux (yearly averages based on OMNI2 data) at 1 AU as a function of time. The time interval starts earlier than the HSTOF observations discussed in this paper because of expected delay between the changes in the solar wind and in the ion distributions in the heliosheath. To compare the observations of Voyager 1 and HSTOF we use the ENA flux averaged over the HSTOF energy range: E 1 E E 2 where E 1 = 58 keV and E 2 = 88 keV. Eq. ( 1 ) then becomes where ⟨ A ⟩ denotes the average over the HSTOF energy range When used for the case of HSTOF, Eq. ( 2 ) must also be averaged over directions of the lines of sight, and over the observation time periods. As explained in Sect. 2 , we divide the HSTOF field of view into four ecliptic longitude sectors (Fig. 1 ). Because of proximity to the Voyager 1 and 2 trajectories, the forward (LISM apex) sector is most suitable for comparison with Voyager observations. A study of the energetic ion distribution in the heliosheath ( Czechowski et al. 2012 ) and the Bonn model of the heliosphere, on which this study was based ( Fahr et al. 2000 ), implies that the thickness L , the energetic ion fluxes, and the neutral density do not vary much over this region. We also consider the two flank sectors. Table 1 lists the hydrogen ENA flux values, which is also illustrated in the Fig. 2 . Table 1 includes also the estimated hydrogen ENA flux from the Voyager 1 direction. It is calculated by substituting for J ion in Eq. ( 2 ) the energetic proton flux J p, V1 at Voyager 1 and for L the distance L V1 = 28 AU between the termination shock and the cliff along the Voyager 1 trajectory. In the HSTOF energy range, Voyager 1 LECP measures only the Z ≥ 1 ion flux , which includes the protons along with the heavier ions. We assume that J p, V1 is approximately equal to . For J Z ≥