DETERMINING THE MAGNETIC FIELD IN THE CORE-MANTLE BOUNDARY ZONE BY NON-HARMONIC DOWNWARD CONTINUATION

Abstract

The length of day and the geomagnetic field are clearly correlated over decadal periods (10–100 yr). Provided the electrical conductivity of the lower mantle is sufficiently high, a considerable part of this correlation can be explained by electromagnetic core–mantle coupling. Investigating the associated core–mantle coupling torque and fluid velocity fields near the core surface, as well as the interpretation of the observed time lag between length of day and geomagnetic field variations requires the calculation of the temporally variable magnetic field near both sides of and on the core–mantle boundary by solving the magnetic induction equation. Such a solution presents a downward field continuation that has a non-harmonic character if the electrical conductivity is accounted for.