Abstract :
The positive and negative ion composition of the lower ionosphere has been modeled globally by combining the 2-D neutral NCAR model with the results of calculated ion production and the chemistry of positive and negative ions. Besides the relevant ion production sources the ion model considers the gas phase chemistry of 30 positive and 30 negative ion species. Results from this model and selected comparisons with measurements are presented. Differences as well as common features between the calculated electron densities and the IRI-model are also discussed in this context. The model offers the possibility to validate the abundance of selected minor constituents used from the neutral NCAR model such as nitric oxide, atomic oxygen, water vapor and O2(1Δ). The abundance ratio f+ of molecular ions to cluster ions is important to characterize the upper border of the D-region. A pronounced seasonal and latitudinal dependence of f+ was found, which is mainly due to temperature variations and to meridional transport of neutral species (NO, O, H2O).
