Coincident multi-point observations of the E- and F-region decametre-scale plasma waves at high latitudes

Abstract

Presented is an extensive analysis of the E-region backscatter observed at magnetic latitudes 75°–80°N by the PolarDARN component of the Super Dual Auroral Radar Network (SuperDARN). The statistical occurrence characteristics of the short-range echoes reveal significant differences from those of the auroral and sub-auroral SuperDARN radars. In particular, most backscatter is detected in the midnight sector in the closest range gates where the geometric magnetic aspect angles are in excess of 10° where no backscatter is normally expected. One explanation offered is that intense ionisation layers significantly refract the radar waves allowing a regular detection of the backscatter from the nearest range gates. A statistical analysis of the spectral echo types within the PolarDARN dataset showed strong similarities with the auroral SuperDARN radars, despite significant differences in the geometric aspect angle coverage. The low-velocity echoes dominated the datasets, while the high-velocity echoes were observed rather sporadically in the morning sector. The location of the PolarDARN radars relative to the more-equatorward SuperDARN radars facilitates the use of a new experimental setup that has coincident and simultaneous HF radar coverage of the E and F regions on the same magnetic field lines. Using this configuration, the SuperDARN plasma flow measurements are employed to investigate the E-region phase velocity dependence on the electric field strength and the flow angle at multiple locations. By employing elevation angle estimates, a marked decrease in the normalised phase velocity with decreasing altitude is observed, which provides direct support to the previously suggested collisional depression of the irregularity phase velocity. It is also shown that the normalised phase velocity is smaller for higher electric fields, which is interpreted as being due to a change in the contribution of the convective effects to the plasma wave growth at decametre scales.