AURORAL RADAR BACKSCATTER AT OFF-PERPENDICULAR ASPECT ANGLES DUE TO ENHANCED IONOSPHERIC REFRACTION

This paper studies the effect of ionospheric refraction upon auroral r adar backscatter under conditions where the aspect angle appears far f rom ideal, i.e., when the unrefracted ray path trajectory is at least a few degrees from the perpendicular to the Earth's magnetic field. It is found that wave trapping by curved electron density layers can cau se ionospheric refraction as large as 20 degrees, even at 150 MHz. Thi s suggests that many so-called off-orthogonal VHF echoes are in realit y due to backscattering at near-orthogonal aspect angles, the discrepa ncy arising from increased ionospheric refraction by curved or tilted layers.