On the night time ionic recombination in the ionospheric F-region

The influence of ionic recombination of negative and positive atomic oxygen ion pairs on processes in the F-region of the nighttime ionosphere is analyzed. In particular, the possible effect of ionic recombination on the natural optical emission of oxygen in the ultraviolet region is discussed. Variations in the ratio of ionic to radiative recombination is examined. This ratio is greater than unity in the part of the F-region, beneath the maximum, and is slightly less than unity in the part near the maximum; it has negligible value at altitudes of 500-600 km. The geographical and seasonal variations on the ratio are shown; the influence of ionic recombination increases significantly during increased solar activity. Numerical calculations are based on the CIRA-72 and IRI models. In each case, up to an altitude of about 800 km, the integral effect of ionic recombination is found to be significant compared to the effect of radiative recombination in a vertical column with a cross-section area of 1 sq cm.