Controlling role of maximum usable frequencies in ionospheric informatics

Considering peak parameters of the ionospheric F region which might be observed/modelled/predicted a few relations connecting such data are pointed out. It is pointed out that the sub-peak semi-thickness of the profile depends on the peak height of the F2-layer. The dispersion range of monthly measurement of the MUFs (maximum usable frequency) inferred from M(3000)F2 is compared with that of the critical frequencies foF2 and found to be larger. The inverted Shimazaki formula yields straight-forward values of MUF from the F2 layer critical frequency and the peak height ZmF2. When comparing MUF-3000 values scaled routinely from ionograms with those obtained from foF2 and ZmF2 of the profile analysis, good agreement is obtained. It is felt that the parameter MUF-3000 is a valuable means for checking data obtained by measurements or by models or by predictions.