Two-level model for formation of night ionosphere of Venus from radio occultation experiments

Although available data from radio occultation experiments (Venera-9 and Venera-10 (1975) and Pioneer and Verna stations (1978)) show that during years of low solar activity the electron concentration in the night ionosphere of Venus has two maxima (is two-level), the reasons for this were not clarified. A two-component diffusion model (0(+) and 0(+)₂₎ is proposed to describe the natural formation of the one- or two-maximum electron concentratioons as a function of physical conditions in the Venusian atmosphere. The basic idea is to find those conditions in which 0(+) plasma moves from the day side to the night side, in which the upper maximum formed in a descending stream of 0(+) ions stops at a given maximum forming in the descending stream because of the 0(+)2 ions formed as the result of chemical reactions between the 0(+) ions and CO2 molecules. The mathematical apparatus is described. The consistency of the model is checked against typical profiles having one or two maxima. Specific experimental results are discussed in terms of electron concentration and temperature of the neutral atmosphere and the correctness of model calculations is shown. It is intended to use the model also to investigate the contribution of epithermal electrons in the formation of the Venusian night atmosphere.