Review of auroral currents and auroral arcs

Knowledge on the generator producing electric current is essential to understand auroral arcs, since the energy flow into the acceleration region can be traced back to the generator. The types of current postulated to close the auroral current systems include: (1) current due to pressure gradients; (2) polarization current; (3) current in the conjugate ionosphere; (4) current on the magnetopause. The forces driving these currents, which compose the generator, are (1) diamagnetic repulsion of plasma by the earths field; (2) inertia force as a flux tube gains and loses momentum due to the interaction with the ionosphere; (3) magnetic stress due to the conjugate points which are not those required for a minimum energy magnetosphere, possibly resulting from the ''mismatch'' of field lines during reconnection; (4) discontinuity in magnetic stress at the magnetopause arising from either the different histories of flux tubes or topological features such as the cleft, corresponding to each current. (Yoshimori, M.)