More information about the structure of the current system can be gained from looking at the vertical
component of the magnetic field perturbation. Underneath an uniform infinite plane current sheet
the vertical component is exactly zero due to the magnetic perturbations from current elements on either
side of zenith cancelling each other out. If the current sheet is spatially limited then the vertical
component of the magnetic perturbation increases in magnitude towards the edges. A limiting example
of this is the line current. Here the horizontal component maximises directly underneath
the current and the vertical component is zero but the vertical component goes through a maxima and a
minima to either side of the line current as the horizontal component decreases. Hence the horizontal
components of the magnetic perturbation vector indicate the orientation of the ionospheric current and
the vertical component indicates its spatial uniformity and relative location. More advanced analysis involves deriving a more exact current distribution that describes the observed magnetic field perturbations. However, any magnetic field perturbation does not have a unique ionospheric current distribution associated with it. Therefore the inversion process is basically educated guesswork. |

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