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A review of ionospheric currents, the external part of geomagnetic solar quiet (Sq) variation and the internal part of the induced current within the Earth, has been carried out. The theoretical background has been reviewed, and the method of analysis, specifically the spherical harmonic analysis (SHA), is presented. Various works are reviewed and fully discussed. It has been noted that a new model of the Sq current system could be used to obtain a mantle electrical conductivity profile for hemispheres. It is suggested that further research work be carried out in other hemispheres using similar models for more robust interpretations.