High-resolution radar measurements of turbulent structure in the low-latitude E region

VHF radar observations with high range and time resolutions of 150 m and 2 s were made to study the large-scale plasma turbulence in the low-latitude E region over Gadanki. The observations are presented in the form of Dopple r spectra, height-time-intensity (HTI) maps and height-time-Doppler velocit y plots. The daytime E region is found to be unstable mostly in the lower p art (<100 km) over a narrow altitude range and manifesting as discrete scat tering layer, in contrast to large-scale turbulent structures observed over Jicamarca. During nighttime, however, while thin layered structures simila r to that of daytime are dominant in the lower part of the E region, the up per region is found to be unstable over a wide altitude range showing signi ficant large-scale turbulent structures that are bf wave type, and also occ asionally plume type resembling that of spread F. The HTI maps show that th e large scale structures have vertical wavelengths ranging 1 to 2 km and pe riods of few tens of seconds. The Doppler velocities associated with the pl ume type structures are upward and wave-type peturbations are downward with values mostly in the range of 50-100 m s(-1) which are considerably lower to that observed at Jicamarca. The velocity spectral widths ranging 100-150 m s(-1) are also found to be significantly lower compared to that reported for Jicamarca. Notwithstanding the differences noted above, the observatio ns presented here seem to conform broadly to that reported for Jicamarca an d also to that generated through the nonlocal nonlinear numerical simulatio n of the gradient drift instability.