Lightning as the excitation mechanism of the resonance

Lightning is the primary source of energy that keeps the Schumann resonance running. A special role is played by cloud-to-ground (CG) discharges: their vertical current channel connects the base of the storm cloud with the surface, and during the return stroke a strong, rapidly varying current flows through it.

This vertical current channel behaves like a vertical antenna many kilometers long. It radiates electromagnetic waves into the Earth-ionosphere cavity over a broad spectrum; the lowest frequency components (a few to tens of Hz) correspond to the dimensions of the entire planet and excite the resonance modes of the cavity. Because the channel is vertical, it radiates primarily a vertical electric field, to which the SR modes are coupled Price 2016Sentman 1995.

A single discharge is in itself a short, transient pulse. Only the continuous repetition of many discharges from all over the world keeps the resonance "tuned" and supplies it with the energy it would otherwise lose to damping in the imperfectly conductive cavity.