Satellite measurements of ion composition and temperatures in the topside ionosphere during medium solar activity

Information on both the ion density and temperature is obtained from the analysis of Retarding Potential Analyser data from OGO-4 and Explorer-31 satellites. Results obtained from September–October 1967 data during medium solar activity in the altitude range of 700–2000 km are presented. An attempt is made to describe the major altitudinal variations of ion densities and temperatures in middle and low latitudes. The transition heights, where the heavier and lighter ions are equal, are found to be about 1600 and 1300 km in the middle and low latitudes respectively for daytime and 700 km at night for middle latitudes. Based on the observed data and using diffusive equilibrium as a first order approximation, topside ionospheric composition models are given for the medium solar activity.