Comparison and verification of the different schemes for the ionization-recombination cycle of the ionospheric D-region

This study presents the results of a comparison and verification of three plasma-chemical models of the lower ionosphere, which describe the dynamics of 4, 5, and 8 charged components under calm conditions and during X-ray flares of different classes. As a result of verification of the constructed schemes for the ionization-recombination cycle using data on the propagation of very low frequency signals during 12 X-ray flares, the best agreement with experimental measurements was obtained with the eight-component model of the ionospheric D-region. On two of the four paths, this model successfully simulated the qualitative and quantitative response of the amplitude-phase characteristics to solar flares in the C, M, and X classes. In contrast to the eight-component model, four- and five-component models are of limited accuracy which could not be noticeably increased by correcting the ionization rate calculation or the input values of the neutral parameters of the atmosphere.