Abstract
Cooperative UK Twin Located Auroral Sounding System Finland HF radar observations of E region coherent spectra are presented for several events. The Burg spectrum method is applied to study microstructure of the spectra. It is discovered that many spectra are two‐peaked, and quite often there is a systematic pattern in their occurrence; the double‐peak echoes are typically observed at intermediate and far ranges of the E region echo band and at ranges farther than the power maximum in the range profile. The typical separation between the peaks is about 150 m/s and hardly changes with the azimuth of observations. Velocities of two components in a double‐peak spectrum are typically larger and smaller than the velocity of the unresolved spectrum and single‐peaked velocity of echoes at shorter ranges. It is hypothesized that the two components of the echoes occur because of signal reception from the top and bottom of the electrojet layer.
Highlights
We concentrate on three E region events observed with the Cooperative UK Twin Located Auroral Sounding System (CUTLASS) in Northern Scandinavia
Two of the events were previously studied by Danskin et al [2002] and Koustov et al [2002] by considering only the standard SuperDARN FITACF velocities
We repeat that the CUTLASS Finland radar operated in the fast common mode with a full scan through 16 beam positions being completed in 1 minute
Summary
[2] Recent observations of HF auroral coherent echoes with the Super Dual Auroral Network (SuperDARN) coherent radars [Greenwald et al, 1995] have shown the great potential of these radars for studies of the plasma physics of E region irregularity formation [Milan and Lester, 1998; Milan et al, 1997, 2001; Jayachandran et al, 2000; Koustov et al, 2001a, 2002; Uspensky et al, 2001; Makarevitch et al, 2001, 2002a]. 5. Azimuthal Distribution of Double-Peak Echo Occurrence [19] The data presented in Figures 2 and 3 refer to one beam/direction of observations. [22] In Figure 5 the power of short-range echoes (Figure 5a) and their FITACF velocity (Figure 5b) as well as the double peak occurrence (Figure 5c) and the separation between the peaks (Figure 5d) are given for all Hankasalmi beams during two hours of observations, 1400 – 1600 UT. For this reason and because of unusually strong velocity of the peak we think that this component of the spectrum corresponds to radar detection of the Type 1 echo This means that, generally speaking, some double-peaks reported in this study could be interpreted in terms of the azimuthal convolution of Type 1 and Type 2 scatter. More work is needed on this aspect by involving SuperDARN radars observing along the L shells where Type 1 echo detection is more likely
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