The polar ionosphere of Venus near the terminator from early Pioneer Venus orbiter radio occultations

Fourteen profiles of electron density in the ionosphere of Venus were obtained by the dual-frequency radio occultation method with the Pioneer Venus orbiter between 5 and 30 December 1978. A region of almost constant electron density above approximately 250 km was detected. The ionopause height is found to vary from about 300 to 700 km. The structures of the profiles are consistent with models in which O2(+) dominates near the ionization peak and is replaced by O(+) at higher altitudes.