Comparative study of numerical simulations of the solar wind interaction with Venus

The assumptions and peculiarities of the numerical codes, as well as the spatial resolution of the gas-dynamical and hybrid simulations which are available at present are discussed. As found the present day estimates of O+ ion production rates which can effect the bow shock geometry as intensively as observed by Pioneer-Venus-Orbiter are controversial. The disagreement of the gas-dynamical simulations by Breus et al. (Planet. Space Sci. 40, 131–138, 1992) and Stahara and Spreiter (Venus and Mars: Atmospheres, Ionospheres and Solar Wind Interactions, Geophysical Monograph 66, p. 345. AGU, 1992) is a result of different numerical implementation of the flow tangency condition which does not permit the specification of the equation of state p = p(ϱ) at the impenetrable obstacle. The numerical code by Breus et al. uses the reflection procedure for the implementation of the flow tangency condition and is insensitive to the equation of state at the obstacle surface. The reflection procedure does not employ explicitly the boundary conditions at the obstacle which the Stahara and Spreiter code does. As a result Stahara and Spreiterʹs (Venus and Mars: Atmoshheres, Ionospheres and Solar Wind Interactions, Geophysical Monograph 66, p. 345. AGU, 1992) simulation is in agreement with observations only in the case of an unreasonable value of the electron impact ionization: in several times of the photoionization within the magnetic barrier at Venus. Breus et al. (Planet. Space Sci. 40, 131–138, 1992) agree well with observations if the electron impact ionization is 60–70% of the photoionization there. Brecht and Ferrante (J. geophys. Res. 96, 11209–11220, 1991) simulated an insignificant effect of the magnetic barrier on the shock geometry. However this simulation is unable to estimate the O+ ionization rate to fit the hybrid model with observations. The cells employed by Moore et al. (J. geophys. Res. 96, 7779–7791, 1991) are larger than the thickness of the magnetic barrier region estimated from the magnetometer data by Zhang et al. (J. geophys. Res. 96, 11145–11153, 1991). Thus Moore et al. cannot simulate the magnetic barrier region properly and their prediction of an insignificant effect of the mass-loading under any expectable O+ ion production rate should be revised.