The latitudinal variation of the electron concentration in the topside ionosphere in winter

Abstract

Data obtained in the American sector by means of Alouette I during the winter of 1963–1964 are used to investigate the latitudinal variation of the electron concentration at the F2-layer peak and at 1000 km. By day, the values of ƒ 0F2 appear to depend on geographic latitude rather than on magnetic dip, but at night the Earth's magnetic field controls the latitudinal variation of critical frequency. The daytime ƒ 0F2 values are enhanced at latitudes where the magnetic dip is 60°; this enhancement, which has been reported by previous authors, does not exist at 1000 km. The daytime high-latitude electron concentration values for 1000 km are extremely variable; particularly large values are observed during magnetically disturbed conditions. Ground-based ionosonde data have been used to show that the main high-latitude trough occurs at 57° invariant latitude in both the American and Asian sectors.