Statistical analysis of the critical frequency foF2 dependence on various solar activity indices

Abstract

A detailed analysis of the description of the F2-layer critical frequency foF2 dependence on solar activity indices (proxies) is analyzed. To do that, the results of the vertical ionospheric sounding at Juliusruh station during two winter months (January and February), two equinox months (March and October), and a summer month (June) are considered. Five solar proxies: Ly-α, MgII, Rz, F30, and F10.7 are analyzed. The determination coefficient R2 according to Fisher F-test is used as a measure of the quality of the description of the foF2 dependence on SA by each of the proxies It is found that a well pronounced diurnal variation in the R2 is observed: this value is higher at the near-noon hours than at night. In other words, all indices describe better the foF2 behavior in the daytime than at night. A well pronounced diurnal variation in R2 is observed also for four proxies in the equinoctial months, whereas that variation is pronounced much worse for Rz: a strong scatter of the R2 values is seen. A diurnal variation in the R2 is absent completely in June: jumps of that value from one hour to another are observed. A few examples of the same analysis are presented also based on the Boulder stations data. The aforementioned analysis allows us to conclude that the most reliable SA proxies for description of the foF2 dependence on SA are (in the declining order) F30, MgII, and Ly- α.