High‐frequency magnetospheric sounding at EISCAT: Some trials and their implications

Abstract

The results of some recent experiments employing the EISCAT HF “heating” facility at Ramfjordmoen, near Tromsø, Norway as a HF radar transmitter are described. The motivation for the experiments was the detection of “conjugate echoes” caused by geomagnetic field‐aligned ducting of the HF wave in the magnetosphere and reflection from the magnetically conjugate ionosphere. No such echoes were detected during the experiments, which is probably to be expected from consideration of the plasma density gradients required to sustain guidance of the waves at the low HF frequencies involved. However, echoes were obtained at ranges which could be consistent with backscattering from ionospheric irregularities in the equatorial and southern auroral regions; this is similar to spread‐Doppler clutter observed by large over‐the‐horizon radar (OTHR) systems. The experimental technique is described and the results discussed with a view toward future attempts to sound the lower magnetosphere using high‐power HF transmitters.