Distinguishing ionospheric models using Schumann resonance spectra

A number of models for Schumann resonance (SR) behavior in uniform approximations of the real Earth‐ionosphere cavity now populate the literature. These models are treated in terms of variously formulated propagation parameters: as the complex eigenvalue of the propagation problem, as the complex incident angle's sine, as the phase velocity and attenuation rate, or as a pair of complex characteristic altitudes. This study compares a priori theoretical propagation parameters with the corresponding quantities recovered from calculated Schumann resonance spectra by means of Lorentzian spectral fits. To estimate the ultimate accuracy of the recovery procedure, the influence of source‐receiver separation is excluded by assuming a globally uniform distribution of lightning sources. The comparisons show a practically acceptable agreement, within several percent, agreement between recovered and a priori parameters for all models studied. When judged against real Schumann resonance observations, these results shed light on problems with certain models. More importantly, the results reaffirm the ability of procedures based on SR observations to resolve global features of the ionosphere's state and structure.