This current flows in the conducting layer of the Earth's atmosphere known as the
Electrical current is the differential motion of oppositely charged particles. There are three
main forces that give rise to the differential motion of ions and electrons in the ionosphere and
hence to current: Lorentz, drag and electrostatic forces.
The ionospheric current is made up of two components: Pedersen and Hall currents flowing at right angles to each other. In addition, these currents are fed by currents flowing into the ionosphere along magnetic field lines - Kirchoff's Law.
A ground magnetometer can detect these ionospheric currents. The equivalent current method does not allow us to distinguish between these currents, but it turns out that a ground magnetometer is usually most sensitive to the Hall current. This is because the ground magnetic perturbation from the Pedersen current is almost exactly cancelled by the ground magnetic perturbation from the field-aligned currents that feed it from the magnetosphere In fact, for a uniform conductivity, horizontal ionosphere and a uniform vertical magnetic field the two magnetic perturbations exactly cancel everywhere on the ground (McHenry and Clauer, 1987; and references therein).
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