Aperiodic Large-Scale Disturbances in the Lower Ionosphere. Ionosonde Observation Results

We present the observed disturbances of the parameters of the ionosphere affected by high-power radio waves from the SURA heating facility. Ionosondes located in Nizhny Novgorod and Moscow (Russia), Kharkov (Ukraine), and Pruhonice (Czechia) were used for the observations. The diagnostic tools were from 560 to 2200 km away from SURA. Additional ionization layers with a cutoff frequency of 2.6–3.4 MHz were occasionally observed on the ionograms of the Nizhny Novgorod and Moscow stations. The effective altitude of these layers was 120–160 km and the true altitude was about 110–130 km. The occurrence of additional ionization layers below 100–130 km was controlled by an increase in the minimum observable frequency (MOF). For the Moscow station, the MOF increased by about 1 MHz in the daytime and almost did not change in the night time. MOF variations on the ionograms of the Kharkov and Pruhonice stations were less significant (0.3–0.4 MHz) in all time of the day. The observed effects are most probably due to the midlatitude precipitation of electrons from the inner radiation belt, which increased the electron number density in the ionosphere, absorption of the sounding radio waves, and the MOF. Estimated particle flux density was 10⁸–10⁹ m⁻² ·s⁻¹. The electron number density in the daytime increased by a factor of 2–3.