SOLAR-WIND PROTON FLUX LATITUDINAL VARIATIONS - COMPARISON BETWEEN ULYSSES IN-SITU DATA AND INDIRECT MEASUREMENTS FROM INTERSTELLAR LYMAN-ALPHA MAPPING

We compare the solar wind proton flux latitude dependence derived in t he past from the interstellar neutral H distribution in the inner heli osphere from Lyman alpha observations with recent ''in situ'' solar wi nd observations by Ulysses [Goldstein et al., 1995, Phillips et al., 1 995, 1996, J.L. Phillips, private communication, 1996]. We find common features, such as a significant proton flux decrease with increasing heliographic latitude (about 30%) in the low-latitude regions and broa d ''plateaus'' of low particle fluxes (2.0 - 2.5 x 10(8) protons cm(-2 ) s(-1)) around the poles. We use our model of interstellar H distribu tion under the influence of a multiparameter, latitude dependent solar wind to investigate the effects of a solar wind distribution matching as closely as possible the south heliographic Ulysses observations. F or the first time, multiple scattering is included in such an anisotro pic model. The Ulysses-type wind is found to produce a secondary minim um of Lyman ct intensity in the upwind direction, something already ob served near solar minimum of activity. However, the modeled feature ha s a larger amplitude than the observed one, probably an indication of smoothing due to the combination of solar rotation and waviness of the neutral sheet. The total solar wind particle flux and the full Sun-av eraged ionization rate of the interstellar neutral H are estimated in various cases. For identical equatorial and polar fluxes, the existenc e of broad plateaus results in a significant reduction of the average neutral H ionization (and then of the ionization cavity) when comparin g with models using a classical ''harmonic'' dependence with latitude. As a result, the downwind cavity is less depleted. This may partially explain some discrepancies between the expected and observed Lyman rr emissions from the interplanetary hydrogen cavity, in particular, the excess of emission from the downwind cavity compared with the classic al model.