Challenging the multiple definitions of auroral electrojets

We present a comparison between magnetic field perturbations from Hall and divergence free currents. Historically the auroral electrojets have been studied using an array of techniques. The workhorse has been, and remains to be, the groundbased magnetometers. As a consequence several different definitions of what the electrojets are; Ground based magnetic field perturbations rotated 90 degrees. Hall currents. Hall, Pedersen and field aligned currents. Divergence free currents. It is analytically known when the equivalent current produced by magnetic field measurements on ground are identical to the Hall current i.e. Fukushima’s theorem. However, the inherent assumptions do not hold in reality. The purpose of this study is to understand when, where and why these concepts agree and disagree. The comparison is done using MHD simulation (Gamera) which provides contributions to the magnetic perturbation from various decompositions of the ionospheric currents.