Nature of the Lower D Region of the Ionosphere

Abstract

IONS in concentrations of about 10² to 10³ cm⁻³ have been measured during day and night by means of rockets in the mesosphere. The resulting data have been used by Bragin et al.^1,2 as the basis of two hypotheses: (1) that the high concentrations of ions below 90 to 80 km is produced during both day and night by the ionising agent (the flow of particles with medium energies) and (2) that the D region of the ionosphere below 80 km is formed in daytime because of the photodetachment of electrons from negative ions by photons of sunlight with energies below 10 eV. No assumptions have been made about the nature of the negative ions involved. The data for the actual aeronomic reactions used were as follows: (1) the rate coefficient of the detachment of electrons from the negative ions was assumed to be 10⁻² to 5 × 10⁻¹ s⁻¹; (2) the rate coefficient of the detachment of electrons from negative ions by processes other than photodetachment was assumed to be of the order of 1 s⁻¹ at 60 km, and 10⁻¹ to 10⁻² s⁻¹ at 80 km; (3) the rate of attachment of electrons to the molecular oxygen was assumed to be 1.5 × 10⁻³⁰ [O₂]² cm³ s⁻¹, where [O₂] is the concentration of the molecular oxygen corresponding to the standard atmosphere.