Core Flows inferred from Geomagnetic Field Models and the Earth’s Dynamo

Nathanaël Schaeffer (1) , Maria Alexandra Pais (2) , Estelina Lora Silva (2)

1 Géodynamo
2 CFC - Centro de Física Computacional

Are the presently inverted large scale core velocity fields enough to explain the geody-namo? Our kinematic dynamo calculations use large-scale, quasi-geostrophic (QG) flows inverted from geomagnetic field models, which, as such, incorporate flow structures that are Earth-like, as the large eccentric gyre and the anticyclone under North Pacific. Furthermore, the QG hypothesis allows straightforward prolongation of the flow from the core surface to the bulk. We obtain magnetic field growth only when the QG flow is perturbed by magnetic pumping that parameterizes the effect of an internal toroidal magnetic field of Elsasser number Λ on the flow. The magnetic pumping distorts the columnar flow and introduces helicity. Dynamo action is observed for Λ ≥ 0.25 and magnetic Reynolds numbers Rm ≥ 200. This suggests that our large scale flow captures the relevant features for the generation of the Earth's magnetic field and that the invisible small scale flow may not be directly involved in the process. Near the threshold, the resulting magnetic field is dominated by an axial dipole, with some reversed flux patches. Time-dependence is also considered, derived from principal component analysis applied to the inverted flows. We find that time periods from 120 to 50 years do not affect the mean growth rate of the kinematic dynamos.

Keywords: core flow; geodynamo; geomagnetic field; kinematic dynamo

Domains: Geophysics [physics.geo-ph]

Nathanaël Schaeffer, Maria Alexandra Pais, Estelina Lora Silva. Core Flows inferred from Geomagnetic Field Models and the Earth’s Dynamo . Study of the Earth's Deep Interior 2016, Jul 2016, Nantes, France. , 2016. ⟨insu-01351652⟩