Frequency properties of the quasiperiodic variations of midlatitude Es layer traces amplitude

In the present work, we report about long-term measurements of echoes from Es layer performed using ionosonde in Kazan with 1 minute period of ionogram registration. Deep quasiperiodic variations resembling interference beats at certain frequency range in amplitude of echoes from Es layer were observed. A new form of data presentation was introduced, which allowed not only to display clearly the critical frequencies of ionospheric layers, but also to demonstrate the fine structure of ionospheric layers. The beats appeared at 4 MHz in the afternoon and at $2$ MHz at night, and had an extent in the frequency range of $\sim0.5$–$2.5$ MHz. As the sounding frequency increased, the distance between the minima increased from $30$ to $700$ kHz. Occurrence probabilities of echoes from Es layer were determined depending on structural features of the reflection.