Abstract Thermal ion O ++ densities in the outer ionosphere have been studied using data from the mass spectrometer on INTERCOSMOS 24 (project Active, perigee 500, apogee 2500 km, inclination 83 .) and INTERCOSMOS 25 (project Apex, perigee 500 km, apogee 3500 km, inclination 83 .) satellites. Characteristic enhancements in the latitudinal O ++ density profiles have been often observed at middle latitudes. A statistical survey probing their dependence upon magnetospheric and ring current activity (Kp and Dst indices) is presented. The relationship between their position and the plasmapause is analyzed. Simultaneous measurements of thermal electron temperature are discussed.