Electron acceleration in the auroral current circuit

Understanding the mechanism supporting the potential drops that accelerate electrons into discrete auroral arcs has been an outstanding problem in space physics for decades. A few thousand kilometers above auroral arcs the electron density often is well below 106 m−3, and the parallel current density into discrete auroral arcs is often a few µA/m². To carry this current in such a low density plasma, the electrons must be accelerated to high energies, and kV potential drops can be supported by electron inertia alone. We describe how an equatorial MHD generator sets up the auroral current system and creates the parallel potential drop that accelerates auroral electrons to keV energies.