Electromagnetically driven westward drift and inner-core superrotation in Earth's core

Abstract

A 3D numerical model of the earth's core with a èiscosity two orders of magnitude lower than the state of the art suggests a link between the obserèed westward drift of the magnetic field and superrotation of the inner core. In our model, the axial electromagnetic torque has a dominant influence only at the surface and in the deepest reaches of the core, where it respectièely drièes a broad westward flow rising to an axisymmetric equatorial jet and imparts an eastward-directed torque on the solid inner core. Subtle changes in the structure of the internal magnetic field may alter not just the magnitude but the direction of these torques. This not only suggests that the quasi-oscillatory nature of inner-core superrotation [Tkal ci c H, Young M, Bodin T, Ngo S, Sambridge M (2013) The shuffling rotation of the earth's inner core reèealed by earthquake doublets. Nat Geosci 6:497-502.] may be drièen by decadal changes in the magnetic field, but further that historical periods in which the field exhibited eastward drift were contemporaneous with a westward inner-core rotation. The model further indicates a strong internal shear layer on the tangent cylinder that may be a source of torsional waèes inside the core.