A comparison of F-region ion velocity observations from the EISCAT Svalbard and VHF radars with irregularity drift velocity measurements from the CUTLASS Finland HF radar

During August 1998, the UK EISCAT special programme SP-UK-CSUB, which combi nes operation of both the mainland VHF and Svalbard UHF incoherent scatter radars, was run for several hours around magnetic midnight on four consecut ive days. The CUTLASS Finland HF coherent scatter radar was, at these times , operating in a discretionary mode, sounding on all 16 beams, one at high- time resolution. This study presents a comparison of the velocities measure d by coherent and incoherent techniques during the SP-UK-CSUB experiments. Agreement, particularly between the ion velocities measured by the EISCAT S valbard radar and irregularity drift measurements by the Finland radar, is remarkable, thereby validating the scientific integrity of both data sets. This work highlights the substantive contribution to our understanding of t he solar-terrestrial environment which can be made by use in concert of inc oherent and HF coherent scatter radars.