A theoretical interpretation of ion composition measured on board the 'Active' satellite in the European sector during April 10−12, 1990 geomagnetic storm
Abstract. Ion composition measurements on board the ACTIVE satellite during the recovery phase of a strong geomagnetic storm of 10-12 April 1990 revealed extremely high concentrations (up to 103 cm-3) of the NO+, O+2, N+2 molecular ions in the topside F2-region of the European high-latitude zone. Concentrations of O+, N+, He+, H+ light ions were slightly decreased relative to prestorm quite conditions. Theoretical calculations were used to analyze the observed variations in ion concentration. Increased neutral temperature and [O2], [N2] are shown to be the main reasons for the observed ion concentration variations.