Geophysical Implications of the Interrelationship of the Geogravity and Geomagnetic Fields

Abstract

RECENTLY there has been much interest in the geophysical implications of the satellite-determined gravity field, and one suggestion is that the low-degree gravity harmonics are associated with undulations at the core–mantle boundary^1–4. Mathematical formulation⁵ does indicate that any mass anomalies at the core–mantle boundary would be observable in the Earth's external potential. Indirect evidence in favour of this hypothesis would come from a strong correlation between the gravity and geomagnetic fields, because variations in the latter are attributed to sources located in the outer core. Egyed³ pointed out a positive correlation between the satellite geoid⁶ and the geomagnetic secular variations⁷, but Coode and Runcorn⁸ showed that this correlation was negligible when an improved satellite geoid⁹ was used. Hide⁴ has proposed, however, that certain magnetohydrodynamical considerations may suggest low amplitude, long wavelength irregularities in the core–mantle interface.