Abstract

The very first study of the upper mantle electrical conductivity profile in the West African sub region using quiet day ionospheric currents has been carried out. The magnetometer data obtained from a chain of 10 geomagnetic stations installed in the African longitudes during the IEEY 1993 experiment were used.  Spherical harmonic analysis (SHA) was used to separate the internal and external field contribution to the Sq variations. Transfer function was used to compute the conductivity–depth profile for West Africa from the paired external and internal coefficients of the SHA. We found a downward increase in conductivity that rose rapidly from 0.037 S/m at a depth of 100km to about 0.09 S/m at 205 km. This high conductivity region was found to correspond with the global seismic low velocity region-the asthenosphere.

Key words: Electrical conductivity, spherical harmonic analysis (SHA), ionospheric currents, upper mantle, West Africa.