Geodynamo models: Tools for understanding properties of Earth’s magnetic field

Self-consistent models of the dynamo process in the Earth’s core have reached a state where they can be used to understand specific morphological and temporal properties of the geomagnetic field. Even though several parameters in the models are far from Earth values, systematic parameter studies resulted in scaling laws that suggest that the dynamical regime in the models is not dissimilar to that in the core dynamo. In some dynamo models the magnetic field shows a close similarity with the structure of the geomagnetic field at the core–mantle boundary and the models are used to infer the underlying flow pattern inside the core. They support the concept of convection columns aligned with the rotation axis that concentrate magnetic flux into four strong lobes near ± 65 ° latitude, and of rising plumes at the poles that are associated with low magnetic flux and westward vortex motion in the polar cap regions. Predictions for the field strength inside Earth’s core from dynamo models and inferences from observations of short-term changes of the field and changes in Earth’s rotation seem to converge at values of a few milliTesla. Dynamo models support the idea that the inhomogeneous thermal structure of the lower mantle has a significant influence on the dynamo and leads to a breaking of the longitudinal symmetry in the long-term geomagnetic field. In a limited range of control parameters the models show dipole polarity reversals that agree in detail with what is known about geomagnetic reversals, although the precise reversal mechanism in the models remains an open question.