On the height distribution of the ratio of negative ion and electron densities in the lowest ionosphere

Abstract

Recent observations of very small variations of auroral type absorption in the twilight periods are taken as the basis for a study of the height distribution of the ratio of the densities of negative ions and free electrons. It has been found that there are no experimental data to definitely prove that the electron density is appreciably increased when the 70–100 km altitude range is illuminated by visual or near ultraviolet light but not by ionizing far ultraviolet radiation. Possible interpretations are discussed and one of them in some detail. The conclusion is that presently existing consistent observational resulta referable to the variation of nondeviative absorption and of radio propagation conditions during twilight periods can be comprehended in terms of O 2 − as the primary negative ion in the lowest ionosphere, provided the height distribution of the ratio of negative ion and electron densities, λ, is decreased so that even the night profile has the value 1 at about 60 km.