The Relationship of the IG and T Ionospheric Indices to the Solar and Geomagnetic Activity Indices

An analysis of the relationship between the monthly mean ionospheric indices IG and T and the indices of solar (F107) and geomagnetic (Ap) activity based on the massif of these data within 1954-2020 interval is presented. F107 and Ap are the monthly mean flux of the solar radio emission at a wavelength of 10.7 cm and the planetary index of geomagnetic activity Ap, respectively. It is found that the index F = (F107(0) + F107(-1))/2 provides a higher correlation to the ionospheric indices than the indices F107 over the given (F107(0)) or previous (F107(-)(1)) months. The IG and T dependencies on Fin the form of a second-degree polynomials make it possible to reproduce 96% of variations in IG and 98% of variations in T for the analyzed time interval. That is the reason that the additional contribution of Ap into IG and T is weak. Nevertheless, the contribution of Ap into T and IG depends on the time of the year: it is not significant for January and is significant for July. This property of the annual anomaly in the ionospheric parameters by the IG index, apparently, is discovered for the first time. In all considered cases, an increase in Ap leads to a decrease in T and IG, that is, to a mean (global) decrease in the median of the F2-layer maximum concentration and, under equal other conditions, such a decrease is more significant in July than in January. The properties of the dependencies of the IG and T indices on F and Ap are in many aspects similar, but the accuracy of these dependencies is higher for T than for IG.