These currents are caused by the circulation of plasma within the
magnetosphere driven by energy extracted from the solar wind.
Their strength and orientation are strongly influenced by that of the IMF vector. The statistical
distribution of equivalent current vectors is shown in the figure
(Friis-Christensen et al., 1985). Combining this with the idealised conductivity
distribution [condfig] (similar to an empirical one) one can estimate the distributions
of electric potential [potfig], field-aligned current [facfig], total ionospheric current [jtotfig], and
Hall current [hallfig]. The ionospheric currents are generally enhanced in the auroral zones due to
the relatively high conductivity there. These channels of current are referred to as electrojets.
Two strong electrojets can be seen close to 70o latitude, one flowing eastward on the
afternoon side, the other flowing westward on the morning side of the Earth. The magnetic perturbations
seen on the ground are due primarily to the Hall currents, as can be seen by comparing this euqivalent
current vectors shown in the figure here with the Hall currents [hallfig].
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