Validation of F2-layer critical frequency variations in the ionosphere with radio observations of solar bursts

The high-frequency (HF) ionospheric cutoff restricts the possibilities of radio astronomical observations from the Earth, but on the other hand, it allows one to estimate the F2-layer critical frequency of the ionosphere. This effect has been measured using a new active antenna meant for receiving cosmic radio emission in the frequency range 1-40 MHz. The instrument was implemented near the Ukrainian T-shape Radiotelescope, second modification (UTR-2) and serves as a prototype of the HF antenna for a future radio array on the farside of the Moon. We detected directly a storm of solar radio bursts on May 22, 2021 and observed clearly their cutoff due to the ionosphere. For comparison our analysis of the experimental data was supplemented by simultaneous measurements from ionosondes located close to the UTR-2. The distance between the closest ionosonde near Zmiiv (Kharkiv region, Ukraine) and the radio astronomical antenna used in the experiment is 46.5 km. Results obtained from the solar radio records are consistent with the ionosonde data. We show that such an antenna implementation provides us with new opportunities to study the F2-layer critical frequency of the ionosphere.