On the possibility of quasi-vertical radio sounding of the ionosphere in the extremely low frequency band

The experimental measurements show that the state of the ionosphere pronouncedly affects the field of the extremely low frequency (ELF) band in the transition zone. The measurements were performed on the Kola Peninsula at different times of day and in different seasons of 2006. The observed seasonal variations in the results are larger than the diurnal variations. The measured field strength does not tend to the calculated statistical value with decreasing frequency if the effect of the ionosphere is ignored. The possibility of using quasivertical radio sounding of the ionosphere in the ELF band to study the structure and electric parameters of the ionosphere is discussed.