Assuming steady state conditions, the occupation of 9 levels of oxygen-like ions: Ne iii, Mg v, Si vii, S ix, and Ar xi have been computed as a function of electron density and temperature. The following physical processes ...

Evidence is presented to point out that the presence of an elevated F-region with reduced peak electron density in the equatorial region does not always result in the occurrence of spread-F condition in the post-midnight period.