A comprehensive model of the Venus ionosphere

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Abstract
The coupled time‐dependent continuity‐momentum and energy balance equations were simultaneously solved for CO2+, O2+, O+, He+, and H+ densities and electron and ion temperatures for an altitude range of 120–500 km. The solar zenith angle was varied from 0° at the subsolar point to 90° at the terminator. The horizontal bulk transport of ions by neutral winds was included in these calculations, although horizontal diffusion was not. The two‐stream photoelectron transport method was used to find the heating rates for the ambient electrons. The effects of different boundary conditions were investigated, and a nightside ionosphere was calculated with electron precipitation as the source of ionization. The results of these model calculations agree well with measurements in the region of maximum electron density. The topside densities and temperatures are shown to be very strongly dependent upon the energy input at high altitudes. For solar zenith angles greater than 90°, densities and temperatures decrease rapidly, which implies that the nightside ionosphere cannot be maintained by neutral wind driven short‐lived ions carried across the terminator. However, the electron densities on the nightside can be explained in terms of electron precipitation.