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

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 115km are considered while the electron velocity is inferred from the EISCAT ion velocity measurements at 278km. The line-of-si ght (1-o-s) VHF velocity measured by STARE V-VHF los is compared to the ion and electron velocity components (V-io (comp) and V-eo (comp)) along the STARE I-o-s direction. The comparison with V-eo (comp) for the entire event shows that the measurements exhibit large scatter and small positive correlation. The correlation with V-eO comp was substantial in the first half of the interval under study when Y-eO comp was larger in magnitude. The comparison with V-io comp at 110 and 115 km shows a considerable positive correlation, with VHF velocity being typically larger (smaller) in magnitude than V-io 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-io (comp) at 110km can be treated, in the first approximation, as a linear function of the effective backscatter height h(eff) also counted from 110km; h(eff) varies in the range 108-114km due to the altitude integration effects in the scattering cross-section. Our results are consistent with the notion that VHF velocity at large flow angles is directly related to the ion drift velocity component at an altitude h(eff).