Abstract
Abstract. Two Doppler coherent radar systems are currently working at Hankasalmi, Finland, the STARE and CUTLASS radars operating at ~144 MHz and ~12 MHz, respectively. The STARE beam 3 is nearly co-located with the CUTLASS beam 5, providing an opportunity for echo velocity comparison along the same direction but at significantly different radar frequencies. In this study we consider an event when STARE radar echoes are detected at the same ranges as CUT-LASS radar echoes. The observations are complemented by EISCAT measurements of the ionospheric electric field and electron density behaviour at one range of 900 km. Two separate situations are studied; for the first one, CUTLASS observed F-region echoes (including the range of the EIS-CAT measurements), while for the second one CUTLASS observed E-region echoes. In both cases STARE E-region measurements were available. We show that F-region CUT-LASS velocities agree well with the convection component along the CUTLASS radar beam, while STARE velocities are typically smaller by a factor of 2–3. For the second case, STARE velocities are found to be either smaller or larger than CUTLASS velocities, depending on the range. Plasma physics of E-and F-region irregularities is discussed in attempt to explain the inferred relationship between various velocities. Special attention is paid to ionospheric refraction that is important for the detection of 12-MHz echoes.Key words. Ionosphere (ionospheric irregularities; plasma waves and instabilities; auroral ionosphere)
Highlights
The high-latitude ionosphere always has fine structure, with irregularities being present at all heights from the bottom of the D-region to the top of the F-region (Fejer and Kelley, 1980; Tsunoda, 1988)
For the second period between 14:00 and 18:00 UT both STARE and Co-operative UK Twin Located Auroral Sounding System (CUTLASS) echoes were received from the Eregion, and we explore these data
The effect is more pronounced for short slant ranges of
Summary
The high-latitude ionosphere always has fine structure, with irregularities being present at all heights from the bottom of the D-region to the top of the F-region (Fejer and Kelley, 1980; Tsunoda, 1988). Attempts have been made to combine HF (12 MHz) and VHF (50 MHz) observations for studies of E-region high-latitude irregularities (Koustov et al, 2001; Makarevitch et al, 2001). These measurements showed differences in properties of meter and decameter irregularities. Some beams of these radar systems overlap so that a comparison of range profiles of echo characteristics can be performed without any additional assumptions regarding their azimuthal variations In addition to these two coherent systems, the tristatic EISCAT incoherent radar (the main facility at Tromsø) can measure ionospheric plasma parameters in both E- and F-regions. By searching through the common data base (with EISCAT operating in the CP1 mode) over several years, we were able to identify only 2 events of reasonable quality, and only one of these is discussed in this study (this event exhibits more clear features)
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