VLF scattering from red sprites: vertical columns of ionisation in the Earth-ionosphere waveguide

Optically, red sprites are observed as clusters of short-lived (~50 ms) pinkish-red luminous columns, stretching from ~40 km to ~85 km altitude, each about 1 km wide. Red sprite discharges produce columns of ionisation in the Earth-ionosphere waveguide, which can persist for up to ~100 s at higher altitudes. The ionised columns have been observed through “VLF sprites”, perturbations of the phase and/or amplitude of subionospheric VLF transmissions, which can be used to study the electrical properties of the red sprite columns. Previous theoretical studies of red sprite columns have simplified the problem by assuming the columns were of infinite length, or inside a “flat-Earth” waveguide. We present calculations using well-developed VLF propagation methods to describe a finite length sprite inside a realistic Earth-ionosphere waveguide