Electric and Magnetic Fields at the Earth's Surface Due to Auroral Currents

The horizontal components of the electric and magnetic fields due to auroral atmospheric currents are calculated at the surface of the earth. For sinusoidal changes in the earth's magnetic field (Fourier frequency components of actual nonsinusoidal variations), a lower limit of the corresponding earth-surface potential is obtained by considering a line-type auroral current over a nonuniform stratified earth. An upper limit of the earth-surface potential is obtained by considering a current-sheet model of the auroral current, and the same model of the earth. A diagram is constructed that allows calculation of the earth-surface potential for given variations in the earth's magnetic field. Finally, the influence of the earth-surface potential on electric power systems is discussed.