Crossposted at Physics SE
As the surface-ionospheric gap acts as a resonator for electromagnetic waves, it should have several harmonic values from the base, fundamental frequency of 7.83 Hz. These are integer multiples, but there is a limit as to how high the frequency can go for it to have an effect, especially so for the Schumann resonance, as the gap between the lithosphere and ionosphere can change due to events in space, mainly the sun. Hence, what is the maximum range of integer frequency values for the Schumann resonance?