Electric Current Systems for Polar Substorms and Their Magnetic Effect Below and Above the Ionosphere

For polar magnetic substorms, the two‐dimensional current system in the ionosphere and the three‐dimensional systems including the field‐aligned currents in the magnetosphere, are conjectured; both systems have the same geomagnetic effect on the ground but a different effect in and above the ionosphere. The intense westward electrojet along the auroral zone, or oval, is concluded to be mainly the Hall current in the ionosphere, and this is always accompanied by the field‐aligned current system in the meridional plane with a north‐south current segment in the ionosphere. The direction of current flow in the meridional plane depends on the mechanism of its production, whether it is of ionospheric origin or of magnetospheric origin. Recent rocket and satellite measurements of the magnetic field in and above the ionosphere indicate the presence of both these conditions.