A Note on the Changes of the Maximum of Ionization of the F1 Layer Associated with the Sunspot Activity

Abstract

The ionospheric F1 layer, whose behaviour conforms to the standard theory during low and moderate solar activity, shows considerable departure from it when the solar activity is very high. The simple relationship which has been shown to exist between foF1 and the mean Zürich sunspot number (Ratcliffe et al., 1956) no longer holds at very high sunspot numbers that were observed during the current solar epoch. Also, foF1 shows anomalous behaviour with respect to season and geographic latitude, similar to that of the F2 layer, at very high solar activity.