Large-Scale Disturbances in the Lower and Middle Ionosphere Accompanying Its Modification by the Sura Heater

Abstract

We briefly describe the results of the first (undedicated) experiments on studying large-scale (about 1000 km) aperiodic and quasi-periodic disturbances in the lower and middle ionosphere. The main results of modern experiments are listed. Multi-instrument radiophysical observations of large-scale (about 1000 km) aperiodic disturbances in the lower ionosphere and quasi-periodic disturbances in the middle ionosphere, which accompanied the Sura heater action with high-power (effective power 40–95 MW) nonstationary radio emission, were performed in 2017–2018 using partial-reflection and vertical/oblique multipath multifrequency sounding techniques. The observations were performed in the observatories of the V. N. Karazin National University of Kharkov during four heating campaigns in 2017–2018. The aperiodic disturbances in the lower ionosphere had a delay time of 15–18 min and a duration of 5–10 min. The disturbances followed the heater switch-on and off. The nature of these disturbances is discussed. The main effects in the middle ionosphere include the following. When the effective radiated power is no less than 40–60 MW, the Doppler spectra become considerably broader and multipathing appears on radio paths that are 1000 km distant from the heater in 40–60 min after the Sura switch-on. Periodic heating of the ionosphere resulted in periodic variations in the Doppler frequency shift (with a maximum deviation of 0.1–0.2 Hz) and in the signal amplitude. The time delay of the ionospheric response lies in the range 40–60 min, while the relative disturbance in the electron density varies from 3% to 12%. Quasi-periodic variations in the Doppler frequency shift and in amplitude are caused by the generation and propagation of waves with 0.2–1.6 km/s speeds and 15–30 min periods. The 0.2–0.4 km/s speeds, as opposed to the 1.6 km/s speed, are regularly observed. The main directions of the future studies of how large-scale aperiodic and quasi-periodic disturbances manifest themselves in the ionosphere and the studies of how these disturbances affect the parameters of radio waves on remote radio paths are also discussed.