Some studies on the daytime D-region during polar cap absorption

Abstract

Representative profiles of the height distributions of electrons, positive ions and negative ions are presented as well as some critical ionospheric parameters such as the lumped electron loss coefficient ψ and the ratio of negative ions to electrons λ in the height range of 60 to 90 km for daytime polar cap absorption (PCA). A mere change of electron-ion production rate due to the enhanced particle precipitation was found insufficient to explain the behaviour of the D-region observed during PCA. To explain the observed decreases of ψ and the H +·(H 2O) n (NO + + O 2 +) ratio at 80 km, the profile of B, the lumped rate of conversion of NO + to H +·(H 2O) n had to be shifted by about 10 km downwards from the quiet daytime condition. While a decrease in the concentrations of O and O 3 was found to have a minor effect in the chemistry at 80 km, it had a profound effect in the negative ion region. To explain the observed decrease of λ (and hence ψ) from quiet to PCA condition at 60 km the concentrations of O and O 3 should be decreased by a factor of about 1.5–3. The effect of shifting the B profile at this height is negligible. At the intermediate region around 70 km both a shift in the B profile and a decrease in the concentrations of O and O 3 are necessary to explain the observed decrease of ψ and λ.