G.G. Vertogradov – Dr.Sc.(Phys.-Math.), Professor,
Southern Federal University (Rostov-on-Don)
Head of Department, JSC «VNII «Gradient» (Rostov-on-Don)

E-mail: vertogradovgg@gmail.com

V.G. Vertogradov – Ph.D.(Phys.-Math.), Head of Department,
JSC «VNII «Gradient» (Rostov-on-Don)

E-mail: v.vitaly@yandex.ru

The presented paper contains the results of the experimental studies carried out during 2016 on two paths, Cyprus – and Laverton – Rostov-on-Don. The object of the work consisted in measuring variations in the maximum observable frequency on the paths of various lengths and orientations, as well as experimental estimating MUF prediction error when setting the ionosphere state using IRI-2016 model taking into account the global empirical model of sporadic Es layer.

It is shown that the MOFs usually experience short periodic variations with quasi-periods from 30 minutes to 2 hours. The amplitude of fluctuations can reach 2 MHz in quiet ionospheric conditions at midday; during sunrise and sunset, when the terminator passes, the fluctuations on the Cyprus – Rostov-on-Don path may increase up to 5−6 MHz. These fluctuations are associated with the propagation of the travelling ionospheric disturbances at altitudes of the ionospheric F‑region.

Based on the analysis of experimental and calculated data of oblique sounding on mid-latitude paths of various lengths and orientations, it is found that the best results in predicting MUF of individual propagation modes can be obtained by correcting IRI-2016 model using the effective solar activity index.

The standard deviation values of MOFs from their average monthly expectations increase with increasing the path length. Under calm geophysical conditions, the typical standard deviation values are estimated which reach 2.5 MHz.

On the long Laverton - Rostov-on-Don path, IRI-2016 model gives significantly lower MUF values. The situation under the conditions of minimum solar activity cannot be corrected by correcting IRI model using the solar activity index.

In summer, on the long Laverton - Rostov-on-Don path, MOF is provided by the sporadic Es-layer. In case of using only the IRI-2016 model for MUF prediction, without taking into account the parameters of the Es-layer, the error in the prediction of MUFs can reach 5 MHz.

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