Semi-Empirical Modeling of the Venus Ionosphere

Electron density profiles from radio occultation experiments on Venus Express were analyzed using the equations of photo-chemical-equilibrium (PCE) appropriate for heights between 100 and 170km. The results were used to formulate a semi-empirical model for peak electron density (N_max) and total electron content (TEC). Both N_max and TEC exhibit high correlations with parameterizations of solar flux and solar zenith angle (0.98). These results were then validated using data sets from Venera 15/16 and Pioneer Venus Orbiter (PVO)—leading to equally high correlations of 0.996 and 0.98, respectively. Venus' ionosphere is thus the most PCE-dominated ionosphere in the solar system. This strong PCE control of ionospheric processes at Venus allows for N_max and TEC to be used to derive values of equivalent slab thickness (S = TEC/N_max), from which exospheric temperatures (T_ex) at 170 km can be derived. The resulting T_ex values are essentially constant throughout the daytime period, as determined by other techniques.