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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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