A new radar auroral backscatter experiment
In 1982 a new radar auroral backscatter system, SABRE (Sweden and Britain Radar Experiment), commenced operation in northern Europe. Observations with this ground-based system allow estimates to be made of the electric fields in the auroral E-region. As an electric field probe, the coherent radar technique is unique in that measurements are made over a large area (∼200,000 km2) with good spatial resolution (20 × 20 km2) and with a temporal resolution of typically 20 s. The system field of view covers an L-value range 4.3–5.8. This region in the magnetosphere–ionosphere system is now accessible for the first time for detailed electric field studies. We present here observations of two pulsation events.
Mean auroral E-region plasma convection patterns measured by SABRE
Large-scale flows of convective plasma in the Earth's magnetosphere, driven by the external influence of the solar wind, have long been known. The electric fields associated with this convection are mapped along approximately-equipotential field lines to low altitudes, resulting in strong ionospheric flows. Considerable controversy surrounds the detailed pattern of the convective flow in the ionosphere, its dependence on geomagnetic and interplanetary conditions and the resulting magnetospheric topology. Several observations1,2 suggest that this pattern rotates towards earlier local times during magnetically-disturbed periods, but empirically-based modelling failed to detect such an effect and even suggested the counter rotation, towards later local times3. Since April 1982, a new radar auroral backscatter system, SABRE (Sweden and Britain Radar auroral Experiment) has been in operation in north ern Europe4, which allows estimates to be made of plasma convection in the auroral E region over a large area (∼200,000 km2, L = 4–6) with high spatial and temporal resolution. Here we present the flow patterns averaged over this period of radar operation for different levels of magnetic activity, revealing a definite rotation of the whole convection pattern towards earlier local times with increasing activity.
Modelling of Pc5 pulsation structure in the magnetosphere
Abstract Magnetohydrodynamic resonance theory is used to model the structure of the magnetospheric and ionospheric electric and magnetic fields associated with Pc5 geomagnetic pulsations. In this paper the variation of the fields across the invariant latitude of the resonance are computed. The results are combined with calculations of the variation along a field line to map the fields down to the ionosphere. In one case the results are compared with measurements obtained by the STARE auroral radar and show good agreement. The relationship between the width of the resonance region and ionospheric height-integrated Pedersen conductivity is computed and it is shown how auroral radar measurements of Pc5 oscillations could be used to determine ionospheric height-integrated Pedersen conductivity. It is pointed out that from these calculations it would be possible to identify the field line on which a satellite was located by comparing a Pc5 pulsation observed by the satellite, and the same pulsation observed by STARE.