RADIATING CONDUCTING COLUMNS INSIDE THE EARTH-IONOSPHERE WAVE-GUIDE -APPLICATION TO RED SPRITES

Expressions are developed to characterise the scattering of VLF electr omagnetic waves from a finite-length ionised column at some height in the Earth-ionosphere waveguide. This formulation has been examined to investigate the perturbations of VLF transmissions caused by scatterin g from red sprites (very large luminous phenomena observed over thunde rstorms). The idea of a correction factor is advanced to move from a p revious model using infinitely long columns to one with truncated colu mns (50-90 km altitude) inside the waveguide. Using a night-time ionos phere model a quantitative comparison is made between experimentally o bserved and modelled red sprite scattering characteristics. It is foun d that the conductivity of the sprite columns ('spritelets') must be a bout 10(-4) S m(-1) to generate the experimentally observed scattered fields. This Suggests that the electron density of red sprites can be five orders of magnitude greater than the night-time ambient electron density at some heights. (C) 1998 Elsevier Science Ltd. All rights res erved.