Ionospheric quiet-day currents and their effects on the interpretation of upper mantle conductivity – A review

A review of ionospheric currents,the external part of geomagnetic solar quiet (Sq)variation and the internal part of the induced currentwithin the Earth, has been carried out.The theoretical background has been reviewed,and the method of analysis, specificallythe spherical harmonic analysis (SHA),is presented. Various works are reviewed andfully discussed. It has been noted that anew model of the Sq current system could beused to obtain a mantle electrical conductivityprofile for hemispheres. It is suggested thatfurther research work be carriedout in other hemispheres using similarmodels for more robust interpretations.