Abstract
Abstract. During August 1998, the UK EISCAT special programme SP-UK-CSUB, which combines operation of both the mainland VHF and Svalbard UHF incoherent scatter radars, was run for several hours around magnetic midnight on four consecutive 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 measured by coherent and incoherent techniques during the SP-UK-CSUB experiments. Agreement, particularly between the ion velocities measured by the EISCAT Svalbard 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 the solar-terrestrial environment which can be made by use in concert of incoherent and HF coherent scatter radars.Key words: Ionosphere (ionospheric irregularities; plasma convection; instruments and techniques)
Highlights
Irregularity drift velocity measurements by coherent scatter radars have been compared to bulk plasma velocity measurements by other instrumentation, including satellite borne probes and incoherent scatter radars
During the ®rst run, 20 August 2100 UT±21 August 0100 UT, there are a limited number of coherent echoes observed by the Finland radar within the viewing range of the EISCAT Svalbard radar (ESR) and VHF radars, mainly in the lower CUTLASS range gates of the common ®eld-of-view
These observations, made over a four day interval, provide an exceptional opportunity for the comparison of F-region ion velocity with the drift speed of F-region ®eld-aligned irregularities. This is especially noteworthy given that in the work of Davies et al (1999) coherent returns from the Finland radar were observed in the vicinity of the EISCAT site for a time totalling less than 4 h out of an entire database comprising more than 1000 h of measurements from the two most frequently run UHF common programmes, taken over a three year interval
Summary
Irregularity drift velocity measurements by coherent scatter radars have been compared to bulk plasma velocity measurements by other instrumentation, including satellite borne probes and incoherent scatter radars. Haldoupis and Schlegel (1990), and authors referenced therein, con®rmed experimentally previous theoretical evidence that the phase velocity of E-region irregularities, measured with the STARE VHF coherent scatter radar, is limited in magnitude to near the ionacoustic speed. A. Davies and Ossakow, 1983) and observational (Villain et al, 1985; Ruohoniemi et al, 1987; Baker et al, 1990; Davies et al, 1999), suggests that the motion of F-region irregularities measured by HF coherent scatter radars, which, unlike their VHF or UHF counterparts, are not limited to E-region observation at high-latitude due to the refractive nature of radio propagation at HF, is determined by the ambient plasmaow. Davies and Ossakow, 1983) and observational (Villain et al, 1985; Ruohoniemi et al, 1987; Baker et al, 1990; Davies et al, 1999), suggests that the motion of F-region irregularities measured by HF coherent scatter radars, which, unlike their VHF or UHF counterparts, are not limited to E-region observation at high-latitude due to the refractive nature of radio propagation at HF, is determined by the ambient plasmaow This has been found to be true of irregularities generated arti®cially in the F-region by high-power heating facilities This has been found to be true of irregularities generated arti®cially in the F-region by high-power heating facilities (e.g. Eglitis et al, 1998)
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