Night-time ionization in the lower ionosphere—II: Distribution of electrons and positive and negative ions

Abstract

In Part I of this paper we have discussed the nature of the night-time variation of certain ionospheric parameters, such as height, electron density, and absorption at frequencies in the range 16 kc/s-18.3 Mc/s, and have deduced the time and height variations of the (effective) coefficient of recombination in the ionosphere at night for heights in the range 80–110 km. In this paper, we deduce from the observational results presented in Part I, the distributions of various positive and negative ions and of electrons in the lower ionosphere at night. The positive ions are the atomic ions X +, which are only predominant at night, and the molecular ions YZ + that control the daytime ionization. It is found that the concentration of X + increases from a negligible value at about 87 km to about 7 × 10 3/ cm 3 at 110 km. Since such ions recombine with a very small coefficient, their concentrations do not appreciably alter during the entire night. While the concentration of negative ions decreases with the progress of the night, the ratio of the concentration of negative ions and electrons remains constant. There is, however, a rapid fall of this ratio from 80 to 110 km by a factor of about 7 × 10 −4.