Statistical Analysis of the Critical Frequency foF2 Dependence on Various Solar Activity Indices

Abstract

A description of the ionospheric F2-layer critical frequency foF2 dependence on solar activity byvarious indices (proxies) has been analyzed. The results of the vertical ionospheric sounding at the Juliusruhstation during 2 winter months (January and February), 2 equinox months (March and October), and a summermonth (June) are considered. Five solar proxies: Ly-α, MgII, Rz, F30, and F10.7 have been analyzed.The changes in foF2 are compared to the corresponding changes in 1957–1980. The determination coefficientR2 according to the Fisher F-test is used as a measure of the quality of the description of the foF2 dependenceon SA by each of the proxies. It has been found that a well-pronounced diurnal variation in the R2 valueis observed in winter months: this is higher at the near-noon hours than at night. In other words, all indicesdescribe the foF2 behavior better in the daytime than at night. A well-pronounced diurnal variation in R2 isalso observed for four proxies in the equinoctial months, whereas that variation is pronounced much less forRz: a strong scatter of the R2 values is seen. A diurnal variation in the R2 is absent completely in June: jumpsfrom one hour to another are observed. This analysis allows us to conclude that the most reliable SA proxiesfor description of the foF2 dependence on SA at all LT hours are MgII, F30, and Ly-α.