Mean auroral E-region plasma convection patterns measured by SABRE

Abstract

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 observations^1,2 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.