Measurements of the VLF scattering pattern of the structured plasma of red sprites

Analysis of a large number of VLF scattering events associated with sprites results in an average scattering distribution having a strong frontal lobe, and also having strong large-angle scattering. This is consistent with the scattering pattern produced by a theoretical model of the sprite as an array of interacting vertical plasma columns, indicating that some part of the sprite is "hard" and contains complex structure (most likely the "stalactites" seen in optical sprites). Attempting to determine the scattering distribution due to sprites using a high threshold for event detection could result in observation of only the frontal lobe and the minima on either side of it, and not the scattering at larger angles. This problem would be worsened by the use of only amplitude, and not phase, monitoring to detect perturbations, and could lead experimenters to the conclusion that sprites are narrow-angle scatterers, with a smoothly varying diffuse structure.