Fig. 2

The figure illustrates how the S–M dynamo works. a As the solar wind blows across the merged field lines between the IMF and the earth’s magnetic field; the resulting ±eV × B force sets up the dynamo. b The dynamo produces a voltage of about 100 kV or more, which drives a convective motion of plasma in the ionosphere and the magnetosphere. c This convective motion flows along the equipotential contour. The resulting two-cell DD current flows along the equipotential contours, but in the opposite direction of the plasma flow. d The actual DD current pattern is greatly distorted because of the nonuniform and anisotropic conductivity of the ionosphere