Influence of Electrical Conductivity Heterogeneity in the D” Layer on the Flow and Magnetic Field at the Surface of the Core

Abstract:

Short time-scale geomagnetic main field variation such as a geomagnetic jerk may have been influenced by electromagnetic induction and conduction in the lower mantle. In our previous work, we showed numerically that a geomagnetic jerk like variation can be originated from a toroidal magnetic field variation at the CMB and its interaction with the large-scale high electrical conductivity anomaly in the D” layer. The spatial distribution of the acceleration of the geomagnetic field, differential delay time between the local geomagnetic jerk observed in the south Atlantic and corresponding possible geoelectric jerk in the Pacific observed by long baseline submarine cables, and their jerk amplitude (difference of the secular variation before and after the jerk) can be explained if the conductivity in the D” layer beneath south Atlantic is about 10⁴ S/m. 

In this study, the effect of the heterogeneity on the flow in the core and magnetic field is evaluated by using a simple plane model of a heterogeneous mantle based on Buffett (1996) in order to clarify the possible influence of the heterogeneity on the input of the magnetic field at the CMB. Preliminary results suggest that the signature of the magnetic field may be detected as a stationary field at the Earth’s surface if the heterogeneity is planetary scale. It was expected that the flow had elongated structure in the direction of coordinate rotation, but the penetration depth of heterogeneity effect was comparable to the length scale of the heterogeneity due to magnetic damping in the core by the large-scale magnetic field.