Standing electromagnetic waves around the planet

The Schumann resonances are physically standing electromagnetic waves (standing waves) that close around the entire planet. They arise from the superposition of waves propagating in the Earth-ionosphere cavity in both directions around the Earth's circumference.

A standing wave forms when a travelling wave, after circling the planet, returns to its starting point in phase with itself and interferes constructively. A fixed pattern of points with maximum and minimum amplitude is then established in the cavity, one that does not "stand" by chance but is determined by the geometry of the resonator. The frequencies for which this condition holds are precisely the individual Schumann modes.

Unlike an idealized, lossless string or cavity, the Earth's resonator is strongly damped: the ionosphere absorbs part of the energy at each reflection, so without continual excitation the waves would quickly die away. A continuous "source" is therefore needed — global lightning activity, which feeds energy into the cavity and sustains the standing waves. The result is a planetary-scale, weak but measurable electromagnetic field oscillating at the characteristic frequencies of the SR Sentman 1995Price 2016. This picture corresponds to Schumann's original theoretical consideration of the natural oscillations of a conductive sphere Schumann 1952.