The link Q-burst ↔ positive discharge ↔ sprite

The key observation linking ELF transients with optical phenomena is that large positive cloud-to-ground discharges trigger simultaneously a Q-burst in the ELF band and a sprite in the mesosphere. Boccippio et al. (1995) showed the connection between sprites, ELF transients and precisely positive ground discharges. Boccippio 1995

Physically this makes sense: both a sprite and a Q-burst require a large and rapid transfer of charge, such as is provided precisely by an energetic positive discharge. A positive discharge transfers a large positive charge to the ground, which on the one hand excites a strong ELF pulse in the Earth-ionosphere cavity (a Q-burst), and on the other hand creates a sufficiently strong quasi-electrostatic field above the storm for a sprite to form in the rarefied mesosphere.

This triple link positive discharge → Q-burst (ELF) + sprite (optics) is the basis of the indirect detection of TLEs: a captured Q-burst signals an energetic discharge that with high probability accompanied an optical phenomenon in the high atmosphere. This makes it possible to study sprites even where direct optical observation is lacking (see #67).