Trends of the F layer critical frequencies by the data of Slow station during 1932-1995

Variations in the critical frequency of the F2 layer foF2 at the Slow station for the period since 1932 up to 1995 are analyzed for the purpose of determining the long-term changes (trends) in the medium-latitude ionosphere. It is shown that the trends value and sign essentially depend on the number of solar cycles and also on the method for separation of magneto-disturbed conditions. Nonlinear saw-like trend was identified for the foF2 average values