Ionospheric Motions at Low Solar Incidence

Abstract

In a previous publication1, I discussed the behaviour of topside ionospheric densities and scale heights during the sunrise period for the time period May 21 to July 4, 1963. The raw data included more than 1,000 ionograms taken during forty orbits of Alouette I for different solar-zenith-angle ranges between χ=121° and χ=85°. With the assumption that the ionosphere is in a state of diffusive equilibrium, the scale heights were interpreted in terms of combined electron and ion temperature distributions and relative ion concentrations. Here I explore the possibility that the ionosphere is not in a state of diffusive equilibrium, that is, the existence of non-zero ambipolar flux density caused by increases in particle temperature due to increased solar illumination. The scale height distribution obtained previously shows variations with latitude and with solar zenith angles at an altitude of 450 km; these are now interpreted in terms of mean ambipolar flux densities.