Auroral Electric Fields and Currents: Local Manifestations and Global Consequences (Invited)

The large-scale plasma circulation or convection in the magnetosphere and in the magnetically connected low-altitude ionosphere is generally well understood. As first postulated by Dungey, the large-scale ionospheric convection configuration depends strongly on the orientation of the interplanetary magnetic field (IMF). When the IMF Bz component is southward, the convection pattern typically consists of two cells with anti-sunward convective flow across the high-latitude polar cap and sunward return flow at lower latitudes in the auroral zone. When Bz points northward, the convection configuration becomes rather complicated due to the presence of multiple flow cells. While the global convection pattern is controlled by the large-scale interaction between the solar wind and the magnetosphere, distributions of the electric fields and currents in the auroral zone are mostly driven by smaller sale physical processes. One important issue concerning auroral physics specifically and magnetosphere-ionosphere coupling in general is how auroral electric fields and currents are related to the large-scale, global ionospheric convection and current system. In this paper we address this issue by examining the local morphology of auroral electric fields and currents based on detailed satellite observations in the context of global ionospheric convection patterns under both southward and northward IMF conditions. A special emphasis will be placed on the auroral current-voltage relationship.