An interpretation of ion composition diurnal variation deduced from EISCAT observations

Abstract. Physical interpretation is made of the O⁺/Ne diurnal variations in summer, revealed by Litvine et al. (1998) from the EISCAT observations. It is shown that the observed anti-correlation between the Z₅₀ parameter, corresponding to the transition region between 50% of molecular and atomic ions, and the width D_z of the transition, defined as the altitude width between 10% and 90% of the O⁺/Ne ratio, can be reproduced in model calculations and the result of different recombination laws (quadratic in the lower and linear in the upper ionosphere) as well as diurnal variations in the photo-ionization rates.

Key words.Ionosphere (ion chemistry and composition; modeling and forecasting)