The Schumann resonances
(SR) are a set of spectrum peaks in the extremely low frequency (ELF) portion of the Earth's electromagnetic field spectrum. Schumann resonances
are global electromagnetic resonances, excited by lightning
discharges in the cavity formed by the Earth's surface and the ionosphere?
This global electromagnetic resonance phenomenon is named after physicist Winfried Otto Schumann?
who predicted it mathematically in 1952. Schumann resonances
occur because the space between the surface of the Earth and the conductive ionosphere?
acts as a closed waveguide
. The limited dimensions of the Earth cause this waveguide
to act as a resonant cavity for electromagnetic waves in the ELF band. The cavity is naturally excited by electric currents in lightning
. Schumann resonances
are the principal background in the electromagnetic spectrum beginning at 3 Hz and extend to 60 Hz, and appear as distinct peaks at extremely low frequencies (ELF) around 7.83 (fundamental), 14.3, 20.8, 27.3 and 33.8 Hz.
In the normal mode descriptions of Schumann resonances
, the fundamental mode
is a standing wave
in the Earth–ionosphere cavity with a wavelength
equal to the circumference of the Earth. This lowest-frequency (and highest-intensity) mode of the Schumann resonance
occurs at a frequency of approximately 7.83 Hz, but this frequency can vary slightly from a variety of factors, such as solar-induced perturbations to the ionosphere?
, which comprises the upper wall of the closed cavity. The higher resonance
modes are spaced at approximately 6.5 Hz intervals, a characteristic attributed to the atmosphere's spherical geometry
. The peaks exhibit a spectral width of approximately 20% on account of the damping of the respective modes in the dissipative cavity. The eighth overtone
lies at approximately 59.9 Hz. Wikipedia, Schumann Resonances