P.F. Denisenko - Dr. Sc. (Phys.-Math.), Professor, Department of Radiophysics and Space Research, Research Institute of Physics SFU (Rostov-on-Don). E-mail: denis@sfedu.ru A.I. Skazik - Ph. D. (Phys.-Math.), Associate Professor, Senior Research Scientist, Research Institute of Physics SFU (Rostov-on-Don) G.A. Zbankov - Ph. D. (Phys.-Math.), Senior Research Scientist, Research Institute of Physics SFU (Rostov-on-Don)

The influence of large-scale ionospheric irregularities, namely, regular horizontal gradients of the electron density and traveling io-nospheric disturbances (TIDs) on the variation of the level of HF radio waves is investigated near the boundary of the dead zone. Ob-servations of the interference signal structures of extraordinary polarization at a frequency of 9,996 MHz were used for the passage of mid latitude caustics on the path Moscow-Rostov, a length of 950 km. It was found that the TID was the determining factor leading to a further strengthening and weakening of the radiation near the MUF. Quantitative estimations of the effect have been conducted. It was found that contrast may reach 20 dB during observation of the return caustic. Apparently, these estimates are too high due to the fact that the agreement between the experimental and theoretical interference structures was reached only by a single parameter veff. In the future, it is necessary to develop a method of analysis that would take into account the deviation of the effective distance from those obtained by using a spherically symmetric model of the ionosphere.

 

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