The ionosphere of Venus: Strongest control by photo-chemical-equilibrium in the solar system, with implications for exospheric temperatures

Abstract

Profiles of electron density versus height obtained by the radio occultation experiment on Venus Express provide an observational data base suitable for semi-empirical modeling. The basic equations of photo-chemical-equilibrium (PCE) theory can be applied to the altitude range 100-170 km of Venus' ionosphere (Peter et al., 2014). Within that domain, the maximum electron density (N_max) and total electron content (TEC) show very high correlations (0.98) with parameterizations of solar flux and solar zenith angle. Validation using independent profiles from the Venera 15/16 radio occultation experiments yielded an even higher correlation (0.99). Such dominance of PCE ionospheric processes at Venus is the highest in the solar system. This allows for N_max and TEC to be used to derive estimates of the exospheric temperature of Venus' thermosphere at ~170 km.