In this study, Atmosphere Explorer data and model results for the ion and electron temperature and the density of N+, O+, H+, and He+ between 120 and 1400 km altitude are compared for two midlatitude ranges (L=2 and L=4), noon and midnight local time, winter and summer, at solar minimum. The data for the heavy atomic ions (O+ and N+) show that their densities are greater at noon than at midnight for a given season and greater in summer than winter for a given local time. There is only a weak latitudinal variation in the density of these ions. The data show that the light ion (H+ and He+) densities are greater at midnight than at noon and are generally greater in winter than summer. There is a strong latitudinal variation of the light ion densities, with the densities decreasing with increasing latitude. The model densities are in good agreement with the AE densities for N+, O+, and H+. Model He+ densities are lower, by a factor of 2 or more, than the measured densities. Model ion and electron temperatures agree well with the measured temperatures with only a modest increase in plasmaspheric heating. ¿ American Geophysical Union 1995