Regularities in the F-Region of the Ionosphere

Abstract

THE variation of the maximum ionization density (N _max. F ₂) of the F ₂-region of the ionosphere is known generally to depart widely from the √cos χ law of Chapman (where χ is the zenith distance of the sun). It has, however, been recently shown by Ratcliffe¹ that if, instead of N _max. F ₂, the total ion content (per unit cross-section) of the F ₂-region (n _T F ₂) be considered, the variations of the total ion content with √cos χ appear to be more regular. I have followed up this view², and have shown that if, in place of n _T F ₂, the total ion content of the F ₁- and F ₂-region as a whole (n _T) is considered, then the variations of n _T with √cos χ become very much more regular. However, it was observed that on these otherwise regular variation curves (diurnal and seasonal) certain abnormal peaks are superposed. I had provisionally explained these as due to the effects of solar tides, superposing themselves on the variations due to changes in the zenithal position of the sun. In order to check this assumption seasonal variation curves of the monthly mean values of the 24-hr. average total ion content (n̄_T) were plotted (Figs. 1 a, b, c). These seasonal variation curves—from which the solar tidal effects are obviously eliminated—are found to closely follow the corresponding cos χ curves, justifying the assumptions made. The data analysed were for the same three stations—Slough, Falkland Islands and Singapore—as had been studied in the earlier work.