Pick-up ions upstream and downstream of the termination shock

Abstract

Hydrogen pick-up ions produced in the inner heliosphere are convected outwards with the solar wind and suffer energy-diffusion by quasilinear wave-particle interactions. When arriving at the solar wind termination shock, the big majority of these pick-up's passes directly from the preshock to the postshock plasma regime. While crossing the shock these ions suffer a characteristic change in their density and velocity distribution which sensitively reflects the local shock properties. We extend the earlier model calculations to derive the pre-shock and postshock pick-up proton spectrum in the ecliptic plane, taking into account the global structure of the heliosphere and the termination shock. The proton distribution is used to calculate the energetic neutral hydrogen flux and the results are compared with the CELIAS/HSTOF data. There is a satisfactory agreement as regards the flux intensity scale and the directional dependence of the flux. The calculated energy spectrum is steeper than the data.