Dependence of foF2 on Solar Activity Indices Based on the Data of Ionospheric Stations of the Northern and Southern Hemispheres

An analysis of the dependence of the F2-layer critical frequency on solar activity indices that has been started earlier based on the Juliusruh station data is continued. The data of six stations in the Northern Hemisphere and five stations in the Southern Hemisphere are analyzed in this paper. The determination coefficient R² for the foF2 dependence on solar activity in each particular situation (station, month, local time) is taken as a measure of the quality of that dependence. The conclusion that a well-pronounced diurnal variation in R² is observed in the winter months is confirmed for four solar activity proxies: this value is maximum and changes weakly in the daytime but decreases substantially to the nighttime hours. It is found that the F30 proxy is the best solar proxy to describe the foF2 behavior in the solar cycle, whereas the sunspot number Rz is the worst. Based on a comparison of the changes in R² with LT in the same months at stations of the Northern and Southern hemispheres, it is shown that the aforementioned well-pronounced diurnal behavior in R² is observed only in winter and is absent in summer.