Intercosmos-19 observations of an additional topside ionization layer: the F3 layer Original Research Article

Spatial properties of an additional ionization layer in the topside ionosphere were investigated using Intercosmos-19 satellite ionograms. The data under analysis were choosen for equinoctial conditions of the high solar activity period (1979–1981). The F3 layer was detected in a narrow longitude sectors (about 60°) between the equatorial anomaly crests. Its intensity has a maximum just above the equator and decreases poleward within ±10° dip. A nighttime F3 layer was observed as well as the daytime events.