Current vortices are common in the ionosphere, occurring on a range of scale sizes and either static or in motion. They are a natural consequence of localised current flow into the ionosphere from geospace. Current flowing along the magnetic field into the ionosphere is closed by Pedersen currents in the ionospheric plane that diverge from the entry point of the field-aligned current. Assuming a uniform ionospheric conductivity we also have a divergent electric field. This electric field drives a Hall current in the ionosphere at right angles to it and the magnetic field. For a point source of field-aligned current the Pedersen current and electric field point radially outwards and the Hall current flows in circles around the point source. Since the Pedersen current diverges it decreases in strength in proportion to the square of the radius from the point source. Similarly, for the electric field and the Hall current. The associated ground magnetic field perturbations for each of these currents are shown in the figure ( McHenry and Clauer, 1987). Here the ionospheric conductivity is assumed to be uniform. The ground magnetic perturbation is dominated by that due to the vortical Hall currents because those due to the Pedersen and field-aligned currents almost exactly cancel each other out. Examples [vortexeg.wpd] |

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