Numerical simulations of coronal hole-associated neutral solar wind as expected at the Solar Orbiter position

[1] Neutral hydrogen is indicative of the behavior of the main solar wind component formed by protons out to at least 5 R ⊙ . In fact, beyond this distance, the characteristic time for charge exchange between hydrogen atoms and protons becomes larger than the coronal expansion timescale, causing the neutrals to decouple from the charged solar wind. The mean free path of the neutral component rapidly increases with the radial distance so that neutrals generated at heliocentric distances >24 R ⊙ fly unperturbed and eventually are detected by Solar Orbiter (perihelion at approximately 48 R ⊙ ), since their mean free path is long enough to let neutrals reach the neutral solar wind detector. However, the computation of the differential flux shows that the bulk of the flux detected at the Solar Orbiter vantage point mainly comes from about 9 R ⊙ . Neutrals retain information on the three-dimensional distribution of hydrogen at the level where they are generated as the proton velocity distribution is frozen within the generated neutrals and transferred up to the Solar Orbiter position. In the present study, we report our preliminary results from our simulation of the neutral solar wind distribution as predicted at the Solar Orbiter position and considering the evolution of a coronal hole-emerging solar wind whose major parameters are estimated by the Solar and Heliospheric Observatory (SOHO) Ultraviolet Coronagraph Spectrometer (UVCS) experiment. The synergy between corona remote sensing and in situ neutral particle observations will enable us to infer the degree of anisotropy, if any, in the neutral and charged coronal hydrogen close to the Sun.