The behavior of ions in the D and E regions is shown to exhibit large latitudinal and seasonal variations. These are due to the meridional transport of neutral species (NO, O, H2O) which interact with ion chemistry, to temperature variations, and to differences in the solar input and in high-energy particle precipitation. This paper presents a two-dimensional model of the ion composition in the D and E regions, which shows that the lower ionosphere is clearly dynamically controlled. The importance of the latitudinal and seasonal dependence of the nitric oxide concentration is pointed out. The model also shows that noticeable changes in the meridional distribution of ions should be attributed to the variability in the solar irradiance and in the strength of particle precipitation in relation to the 11-year solar cycle.