Theory of auroral electrojets

Two mechanisms are described for the formation of electro jet currents in the auroral zone. Both mechanisms require the existence of magnetospheric convection in which only particles of relatively low energy participate. It is essential to both mechanisms that particles of one sign (positively or negatively charged) should predominate among the energetic ones that do not participate in the convection of the magnetosphere. In the first mechanism the convection of the magnetosphere is taken to be of tidal origin, driven by the electric polarization fields associated with the dynamo current systems. In the second mechanism the convection is assumed to be the corotation of the magnetosphere with the earth, as modified by the solar wind that distorts the geomagnetic field. In both mechanisms the ionospheric currents are a consequence of the relative motion between the less energetic particles that almost fully participate in magnetospheric convection and the more energetic particles whose adiabatic drift motion across the magnetic field is only slightly perturbed by the electric fields associated with the convection of the magnetosphere. If the particles that do not participate are assumed to be the trapped energetic protons observed by Explorer 12 during magnetically quiet days, either mechanism predicts variations of the order of ±50 γ in the horizontal component of the geomagnetic field at auroral latitudes.