Fig. 12

Frequency variation over a week for mode 1. The fundamental Schumann resonance mode (at 7.8 frequency range) exhibits not only resonance frequency variation but also Q factors and peak powers during a day, giving interesting and important observations that motivate further studying and investigation. In Fig. 12, the resonance frequency variation results of the fundamental Schumann resonance mode are shown. The weekly duration of such results indicate that the first mode of the Schumann resonance spectrum exhibits a slow daily variation that ranges from 7.5 to 8.1 Hz caused mainly by the inhomogeneities and the anisotropy in the Earth-ionosphere waveguide