Amplitude variations of the reflected signal during vertical sounding of the ionosphere at middle latitudes

In this paper, we discuss the main types of quasiperiodic variations in amplitudes of a reflected signal during vertical sounding of the ionosphere at middle latitudes. The initial experimental data is vertical sounding ionograms obtained by the Cyclone ionosonde. The ionosonde is located in Kazan (59°, 49°) and in standard mode allows us to receive one ionogram per minute. In the analysis, methods are used to visualize a large flow of ionograms in the form of final maps of the state of the ionosphere (A-, H-, As-maps). We give typical examples of quasiperiodic variations in amplitudes of a reflected signal in ionograms and on A-maps for various types of multipath beatings (polarization and due to signal scattering by ionospheric irregularities). Frequency properties of such beatings are used to estimate the difference in virtual reflection heights between modes of different polarizations with high accuracy, which makes it possible to refine the form of the electron density profile of the lower ionosphere. We have detected a phenomenon rare for the mid-latitude Es layer - beatings of two O modes with different virtual reflection heights. We also present features of quasiperiodic variations in amplitudes of a reflected signal on traces of the transient Es layer. We study possible causes of the appearance of such beatings.