A full-sphere convection-driven dynamo: Implications for the ancient geomagnetic field

The solid inner core of the Earth formed at 2–3 Ga as a result of the gradual cooling of the Earth’s deep interior plays an essential role both energetically and dynamically, in the generation of the Earth’s present magnetic field. In the early stage of the Earth’s evolution, however, the entire core was made of molten liquid. Understanding convection-driven dynamo in a full sphere is hence of importance in elucidating the dynamics of the young Earth and its ancient magnetic field. We present a numerical convection and dynamo model for the full sphere using a finite element method. A large effort is made to efficiently parallelize the dynamo model so that it can take the full advantage of modern massively parallel computers. It is found that sustaining the full sphere dynamo – driven by convective flows in the absence of the tangent cylinder without imposing any boundary conditions at the center – is more difficult than that in spherical shells. Furthermore, the morphology of the magnetic field generated by the full sphere dynamo is largely dominated by non-dipolar components, indicating the structure of the ancient geomagnetic field prior to the onset of inner-core crystallization would be different from the current geomagnetic field.

► The present study presents a numerical convection and dynamo model for the full sphere using a finite element method in the absence of the tangent cylinder without imposing any boundary conditions at the centre.
► It is found that sustaining the full sphere dynamo without the effect of tangent cylinder is more difficult than that in spherical shells.
► We show that the morphology of the magnetic field generated by the full sphere dynamo is largely dominated by non-dipolar components, suggesting the ancient geomagnetic field prior to the onset of inner-core crystallization would be quite different from the current field.