Thermal O^++ Ions according to Mass-Spectrometer Data Obtained from the lnterkosmos-24 and lnterkosmos-25 Satellites. Part I. Analysis of Regularities

The analysis of the data on O^++ ions obtained in the mass-spectrometer experiment on the lnterkosmos-24 and lnterkosmos-25 satellites has shown that under high solar activity conditions the absolute concentrations of O^++ ions in the illuminated summer ionosphere at middle latitudes increase and remain large (>10^2 cm^-3 ) up to apogee altitudes of 2000-2500 km. It is shown that under these conditions in the altitude range of 700-2000 km the concentration of O^++ ions weakly varies with altitude, and the sharp drop of concentration begins at altitudes lower than ~500-600 km. Under summer illuminated ionospheric conditions, there exists a maximum in the latitude dependence of absolute concentrations of O^++, which falls on middle latitudes. As the altitude grows, the position of this maximum shifts to the side of higher latitudes, while remaining within the boundaries of the plasmasphere. The relative concentrations of O^++/O^++ increase with altitude, reaching the value of about 10^-1 at altitudes higher than 2000 km at the maximum of latitudinal distribution near an invariant latitude of 50°. During the main phase of a strong magnetic storm (Kp > 5), the position of a maximum in the latitudinal distribution of concentrations of O^++ ions at altitudes higher than 2000 km shifts to the side of low latitudes. In this case, the absolute concentrations of O^++ and the relative concentrations of O^++/O^++ at this maximum drop. During the storm recovery phase, the additional maximum is sometimes superimposed on the latitude dependence of concentration at invariant latitudes of 50°-55°. This maximum is, apparently, related to the considerable increase of electron temperature at these latitudes.