The continuing rise of periapis has allowed the Pioneer Venus orbiter (PVO) to encounter vast regions of the Venus ionosphere that were not sampled earlier when propulsion was being used to maintain periapis deep in the ionosphere. We have employed the orbiter electron temperature probe measurements from the first seven Venus years (December 1978--December 1982) to devise new empirical models of electron temperature Te and density Ne. Departing from our earlier use of spherical harmonics to describe the solar zenith angle variations of Ne (Theis et al., 1980) we find that this more complete data set can be described better by error functions and exponentials in solar zenith angle and power law variations in altitude. This model represents a significant improvement over the previous models, as it allows the dawn and dusk sectors to be modeled separately, providing more realistic representations of the gradients near the terminators as well as the variations of those gradients with altitude. We employ these models to perform a two-dimensional solution of the momentum equation for the nightward ion flow velocities believed to be largely responsible for the maintenance of the nightside ionosphere. The velocities at the terminator rise from the neutral atmospheric wind velocity (~300 m/s) at 150 km to a peak velocity exceeding 2000 m/s above 500 km, in general agreement with PVO measurements of ion drift in that region.