Models of sub-grid scale turbulence in the Earth's core and the geodynamo

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Numerical models of the geodynamo have become an increasingly important tool for studying the dynamics of the Earth's core. These models have successfully reproduced important features of the Earth's magnetic field, including the dipole dominance and the episodic reversal of polarity. However, it is generally acknowledged that the models are unrealistic in many respects. All of the current models use physical parameters that are very far from Earth-like values. As a consequence, the nature of the dynamics is altered and the potential to address important geophysical questions is limited. We propose a 2-year study to improve the reliability of numerical geodynamo models by making two important departures from current approaches. First, we will employ a finite-element method, which is better suited to parallel computing than conventional spectral methods. Second, we will develop a more sophisticated method for dealing with the effects of unresolved turbulence, based on the scale-similarity model. These models will be developed and tested initially in a plane-layer dynamo model for computational efficiency. However, we plan to adapt the model geometry to the more relevant case of a spherical shell by the end of Year 1.Observations of the geomagnetic field provide a unique probe of the Earth's interior. Even the persistence of the field depends on the nature of convection in the mantle and, possibly, on the existence of plate tectonics at the surface. Better models for the geodynamo are needed to interpret the geological record and to better understand the evolutionary path that brought the Earth to its current state. The development of new research tools will open new lines of inquiry that are not currently possible.