Application of solar quiet day (Sq) current in determining mantle electrical-depth conductivity structure – A review

• Application of Sq current in determining mantle conductivity is extensively reviewed.
• More light is thrown to the understanding of effects of Sq on mantle conductivity (σ).
• Controversy and marked differences exist in σ variation of different methods applied.
• Methods applying 1-D, 2-D and 3-D were also reviewed.
• There is need to combine discussed methods for clarity and resolution of controversies.

This study has extensively reviewed the application of solar quiet day (Sq) current variation in determining mantle electrical–depth conductivity structure, in a number of countries and various hemispheres. The review includes basic theories and methods of analysis. There are few recent works on the determination of mantle conductivity-depth structure using Sq current. Results obtained have yielded very interesting and exciting information, hence, the need for this review. This review is expected to throw more light to the understanding of effects of Sq on mantle conductivity. There is evidence of controversy and marked differences in conductivity variation in the mantle when different methods are applied, from available literature on the application of Sq on mantle electrical depth conductivity. Other methods applying 1-D, 2-D and 3-D were also reviewed and hence, we recommend the need of combining the above methods with Sq method in future work for more robust results. We have discovered that findings emanating from this work could lead to more understanding of application of Sq current in determining mantle electrical depth conductivity structure.