CHARACTERISTICS OF VERY LARGE ASPECT ANGLE E-REGION COHERENT ECHOES AT 933 MHZ

The EISCAT UHF radar system was used to study the characteristics of E -region coherent backscatter at very large magnetic aspect angles (5-1 1 degrees). Data taken using 60 mu s pulses during elevation scans thr ough horizontally uniform backscatter permitted the use of inversion t echniques to determine height profiles of the scattering layer. The la yer was always singly peaked, with a mean height of 104 km, and mean t hickness (full width at half maximum) of 10 km, both independent of as pect angle. Aspect sensitivities were also estimated, with the Sodanky la-Tromso link observing 5 dB/degree at aspect angles near 5 degrees, decreasing to 3 dB/degree at 10 degrees aspect angle. Observed coheren t phase velocities from all three stations were found to be roughly co nsistent with LOS measurements of a common E-region phase velocity vec tor. The E-region phase velocity had the same orientation as the F-reg ion ion drift velocity, but was approximately 50% smaller in magnitude . Spectra were narrow with skewness of about +1 (for negative velociti es), increasing slightly with aspect angle.