The effects of traveling ionospheric disturbances on SuperDARN near range echoes.

Abstract

Traveling Ionospheric Disturbances (TIDs) and Near Range Echoes (NREs) are both natural phenomena observed by SuperDARN High Frequency (HF) radars. This study presents for the first time observations of NREs in the lower E-region whose amplitudes are moderately modulated by medium-scale TIDs propagating in the F-region that have been observed by the same radar at another time in the far ranges. Two events during geomagnetic storms in winter recorded by the SANAE radar and two events during quiet times in summer recorded by the Zhongshan radar, both radars in the southern hemisphere, are described. The Gradient Drift Instability (GDI) proved to be the likely mechanism. The GDI is driven by the velocity difference between neutrals and plasma in the E-region ionosphere, due to the global convection electric field, and can be modulated by the polarization electric field of a passing TID via the near-vertical equipotential magnetic field lines.