Aspect sensitivity of HF auroral echoes

Abstract

A simple model of auroral backscatter from the E region that includes ordinary ionospheric refraction is developed quantitatively. When the resulting computations are compared with experimental HF auroral backscatter data, a lower limit of 6 db per degree in the 15- to 50-MHz region is found for the aspect-sensitive decrease in backscatter cross section with off-perpendicular angle from the geomagnetic field. When combined with recent VHF and UHF results, this result leads to the conclusion that the aspect sensitivity of the E-layer auroral echoes is almost constant between 15 and 1200 MHz.