Some regularities of the ionosphericFregion

It has been shown recently by Ratcliffe that, although the behaviour of the critical frequency (and hence the maximum ionization density) of the F2 region is very irregular, that of its total ion content (in a column of unit cross-section) is much less so. However, the regularities observed by Ratcliffe are confined only to a few stations and disappear when the F1-F2 bifurcation is large. It is shown in the present paper that if, instead of the total ion content of the F2 region, that of the F1 cum F2 region (nT) is considered as a whole, then the regularities become much more marked. Further, the regularities are found to persist for all the three stations considered—Slough (northern hemisphere), Falkland Islands (southern hemisphere), and Singapore (equatorial region)—even when the bifurcation is large. Certain peaks, however, are found to occur on the otherwise smooth variations of the monthly mean values of nT. These are explained as due to tidal effects. The paper also shows that the observed regularities of the composite F region are in conformity with the recent hypothesis that F1 and F2 belong really to one ionized region, being produced by a common ionizing radiation from the sun.