Certain Mode Solutions of Forward Scattering by Meteor Trails

Scattering of a plane wave normally incident on a meteor trail which has a Gaussian radial distribution of ionization is investigated for various line densities by the wave-matching technique. Solutions were obtained by numerical integration methods with the aid of the SWAC, a high-speed digital computer. For a column of low line density, 1013 electrons per meter, scatter in the back direction checks very closely the results of approximate analyses made by previous workers. In the case of a low-line-density column having a diameter comparable to a wavelength, scatter in all other directions for both transverse and parallel electric vector polarization of the-incident wave checks simple theory based on the summation of scattering by individual electrons. The energy back-scattered by a trail of high line density, 1017 electrons per meter, is found to be nearly equal to the energy which would be back-scattered from an equivalent metal cylinder, thus checking previous approximate calculations. The equivalent metal cylinder is also found to be a good approximation to the actual ion column for scattering in other directions, but only in the case of parallel polarization of the incident wave. The results further show that echoes from high-line-density trails in directions other than the back direction may be appreciably higher than would be anticipated. This would tend to confirm certain recent experimental observations of forward scattering from meteor trails.