The separation of the geomagnetic field originated in the core, in the asthenosphere, and in the crust

Abstract

The separation of the field produced by different internal sources can be accomplished by means of the so-called spatial spectrum of the geomagnetic field of internal origin. It is shown how such a rationale, when suitably interpreted, allows to recognize the field that is originated by electric currents that flow either on the Inner-Core Boundary (ICB), or on the Core-Mantle Boundary (CMB), or on the Asthenosphere-Lithosphere Boundary (ALB). It appears crucial, however, to rely on satellite measurements alone, because ground-based and ship- and air-borne records are severely perturbed by the crustal field. Therefore, it is shown, on the basis of a critical reconsideration of a few key-papers in the literature, that the best approach is to avoid mixing together all kinds of measurements. Satellite data are best suited for recognizing the dynamo field, while ground-based, ship- and air-borne records, which are measured much closer to crustal sources, are best suited, after subtraction of the satellite-derived dynamo field, for inferring the geomagnetic anomalies that are to be associated with crustal sources alone.