Mapping the earth conductivity-depth structure of African geomagnetic equatorial anomaly regions using solar quiet current variations

The solar quiet day ionospheric (Sq) current variations observed in Abuja, Bangui and Addis Ababa were used to delineate the mantle conductivity-depth structure along the equatorial African regions. Spherical harmonic analysis (SHA) was employed in separating the internal and external field contributions to the Sq variations. For each of the paired external and internal coefficients of the SHA, we used transfer function to compute the conductivity-depth profile for the region. Strikingly, we observed increased electrical conductivity values in the Earth layers and deep depth penetration. The calculated average electrical conductivity values in Addis Ababa and Abuja are 0.087 Sm−1 and 0.104 Sm−1 at depths of 93 km and 121 km respectively. These values suddenly rose to 0.235 Sm−1 and 0.222 Sm−1 at depths of 440 km and 427 km respectively. In Bangui, the calculated average values are 0.092 Sm−1, 0.144 Sm−1, 0.312 Sm−1 and 0.466 Sm−1 at 96 km, 300 km, 834 km and 1228 km depths respectively. At the greatest depths of penetration of 1412 km, 1385 km and 1278 km in Addis Ababa, Abuja and Bangui, the electrical conductivity attained the highest values of 0.415 Sm−1, 0.467 Sm−1 and 0.515 Sm−1 respectively. Two most Earth conductive layers were discovered in the magnetic equatorial zone. These layers lie between the depth of about 100 and 400 km within the upper mantle and beyond 1200 km in the lower mantle. It can be inferred that the closer one goes towards the Earth magnetic equator; the deeper the Sq current can penetrate the Earth's interior.