Predictions of electron temperatures in the Mars ionosphere and their effects on electron densities

Observations of peak electron densities in the Mars ionosphere are well fit by a simplistic theory that assumes the electron temperature, T-e, at the peak remains constant as solar zenith angle, chi, changes. However, T-e ought to vary with both altitude and chi. Here we use an existing numerical model of ionospheric energetics, which includes both vertical and diurnal variations in temperatures, to predict that T-e at the ionospheric peak is relatively independent of chi. This model accurately predicts the observed dependence of peak electron density on chi, whereas predictions using Viking-based electron temperatures that are held constant with time do not. A simplified analytic model is developed to interpret these results further. It predicts that the difference between electron and neutral temperatures is proportional to the ratio of electron heating rate to electron production rate and proportional to the square root of solar irradiance.