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

Abstract

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 Doppler spectra, height-time-intensity (HTI) maps and height-time-Doppler velocity plots. The daytime E region is found to be unstable mostly in the lower part (<100 km) over a narrow altitude range and manifesting as discrete scattering layer, in contrast to large-scale turbulent structures observed over Jicamarca. During nighttime, however, while thin layered structures similar to that of daytime are dominant in the lower part of the E region, the upper region is found to be unstable over a wide altitude range showing significant large-scale turbulent structures that are of wave type, and also occasionally plume type resembling that of spread F. The HTI maps show that the large scale structures have vertical wavelengths ranging 1 to 2 km and periods of few tens of seconds. The Doppler velocities associated with the plume 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 observations presented here seem to conform broadly to that reported for Jicamarca and also to that generated through the nonlocal nonlinear numerical simulation of the gradient drift instability. Copyright 1999 by the American Geophysical Union.