Abstract
Trends in foF2 are analyzed according to the data of Juliusruh and Boulder ionospheric stations to 2018. It is shown that the use of the traditional solar-activity index, F10.7, leads to an unexplainable foF2 trend if the data for the 24th solar-activity cycle are included in the analysis. It is suggested that the F10.7 index does not correctly describe the solar ultraviolet-radiation variation in that cycle. Correction of that index with the Rz (sunspot number) and Ly-α (intensity of the Lyman-alpha line in the solar spectrum) indices is performed. It is shown that reasonable values of the foF2 trends are then obtained. A similar analysis for hmF2 trends leads to the same results.
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