Evidence of intermediate layer characteristics in the Gadanki radar observations of the upper E region field-aligned irregularities

Abstract

The Gadanki VHF radar observations of the upper E region field aligned irregularities are presented. These are the first observations of low-latitude upper E region irregularities that resemble the characteristics of intermediate layers observed over Arecibo. The most interesting aspect of these observations is their occurrence at altitudes as high as 160 km, which requires an interpretation in terms of their source mechanism. These irregularities were found to trigger about 21 LT first at higher altitude (140-160 km) and propagate downward with time. The signal intensities are found to be lower by about 12 dB and the Doppler spectra narrower by more than a factor of two compared to that of the normal E region echoes. The Doppler velocities are found to be both upward and downward with values less than 40 m s^-1.