Variations of Radio Wave Characteristics in Low-Frequency Portion of Decameter Wavelengths at Quasi-Vertical Incidence

Abstract

Observations of temporal variations in the spectra of Doppler shift in 3.2-MHz and 4.2- MHz radio waves reflected from the ionosphere are presented. The diurnal variation of such observations made around an autumn equinox has been analyzed. Quasi-periodic and aperiodic processes associated with the solar terminator and with ionospheric heating by high-power HF periodic transmissions from the SURA facility have been detected. The periods and amplitudes of quasi-periodic processes agree with the parameters of internal gravity waves. The on/off switching of the high-power transmission is associated with an enhancement of quasi-periodic processes acting in the ionosphere, as well as with an electron density increase. The latter is most likely associated with energetic electron precipitation from the magnetosphere at midlatitudes.