A first comparison of irregularity and ion drift velocity measurements in the E-region

Abstract

Abstract. E-region irregularity velocity measurements at large flow angles with the STARE Finland coherent VHF radar are considered in context of the ion and electron velocity data provided by the EISCAT tristatic radar system, CUTLASS Finland coherent HF radar, and IMAGE fluxgate magnetometers. The data have been collected during a special experiment on 27 March 2004 during which EISCAT was scanning between several E-and one F-region altitudes along the magnetic field line. Within the E-region, the EISCAT measurements at two altitudes of 110 and 115 km are considered while the electron velocity is inferred from the EISCAT ion velocity measurements at 278 km. The lineof-sight (l-o-s) VHF velocity measured by STARE V VHF los is compared to the ion and electron velocity components (V i0 comp and V e0 comp ) along the STARE l-o-s direction. The comparison with V e0 comp for the entire event shows that the measurements exhibit large scatter and small positive correlation. The correlation with V e0 comp was substantial in the first half of the interval under study when V e0 comp was larger in magnitude. The comparison with V i0 comp at 110 and 115 km shows a considerable positive correlation, with VHF velocity being typically larger (smaller) in magnitude than V i0 comp at 110 km (115 km) so that V VHF los appears to be bounded by the ion velocity components at two altitudes. It is also demonstrated that the difference between V VHF los and V i0 comp at 110 km can be treated, in the first approximation, as a linear function of the effective backscatter height h eff also counted from 110 km; h eff varies in the range 108-114 km due to the altitude integration effects in the scattering cross-section. Our results are consistent with the notion that Correspondence to: R. A. Makarevich (r.makarevich@latrobe.edu.au) VHF velocity at large flow angles is directly related to the ion drift velocity component at an altitude h eff .

Aspect angle dependence of the E region irregularity velocity at large flow angles

“…The points at large α , on the other hand, are consistently below (above) the cosine trend at small (large) flow angles. In Figure 4d we also show the trend V N = sinθ/4 (dotted line) suggested by earlier studies by Milan et al [2004] and Makarevich et al [2006a] (see also our section 3.1). One can notice from Figure 4d that the data at the largest aspect angle α = 2.63° highlighted by the solid lines exhibit a general increase with the flow angle and appear to be consistent with this trend.…”

“…Following earlier studies by Kohl et al [1992] at VHF, by Moorcroft [1996] at UHF, and by Uspensky et al [2001] at HF that suggested that the ion drift velocity contribution to the E region irregularity velocity should be considered, Makarevitch et al [2002] interpreted this observation as being consistent with the linear theory formula in the reference frame of neutrals at the largest flow angles, θ ≅ 90°, where V e 0 C ≅ 0 and phase velocity V ph ≅ V i 0 C is independent of α . More evidence on the importance of the ion motions at large flow angles has been presented at VHF [ Uspensky et al , 2003, 2004; Makarevich et al , 2006a], at HF [ Makarevitch et al , 2004] and at small flow angles and large aspect angles at HF [ Milan et al , 2004].…”

Polar summer mesospheric extreme horizontal drift speeds during interplanetary corotating interaction regions (CIRs) and high‐speed solar wind streams: Coupling between the solar wind and the mesosphere

“…In earlier studies reported in the literature, a number of ionospheric signatures of flux transfer events by flux reconnection have been detected in the F region, using for example the Super Dual Auroral Radar Network radars, including fast poleward moving ions (500–2000 m s −1 ) and large turbulence [ Boudouridis et al ., ; Cerisier et al ., , and references therein]. Also, in the E region (110–115 km height) fast‐moving irregularities have been seen using both HF, VHF, and UHF radars [e.g., Makarevich et al ., ]. These are not completely understood but are considered to be the result of plasma‐instabilities (primarily the Farley‐Buneman instability) driven by strong magnetospheric electric fields when the E × B drift speed up to 2000 m s −1 exceeds the ion‐acoustic speed (~300 m s −1 ) [e.g., Gorin et al ., ].…”

HF radar observations of high‐velocity E region echoes from the eastward auroral electrojet

“…In these calculations we used the typical values of collision frequencies obtained using the expressions given by Schunk and Nagy [1980] and the neutral densities taken from the MSISE‐90 (Mass Spectrometer Incoherent Scatter Extended) model [ Hedin , 1991]. Since the SuperDARN radars used were located in various parts of the world and since a data set spanning 3 years was employed in this study, the MSISE‐90 model was run for the time of 1 January 2004, 1630 UT and for the location of 69.0°N, 19.1°E (used by Makarevich et al [2006a]). The resulting values were v i = 726 s −1 and v e = 31243 s −1 .…”