Studies of geomagnetic variations using 3D mean-field dynamo models based on spectral filtering

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The variations of the geomagnetic main field such as drifts, excursions or reversals reflect the complex nature of the motions in the Earth's core. The observed features of these variations should be understood on the basis of sufficiently detailed simulations of the dynamo process in the Earth's core, which consists in very complex interactions of the magnetic field with fluid motions caused by thermal or other instabilities. Despite very impressive progress in this respect, simulations of these processes with material parameters really close to those of the Earth's core are still missing. Our project aims to study the time behavior of the geodynamo on the simpler level of mean-field dynamo models. However, a new mean-field concept is used, with mean fields defined by filtering of the multipole spectra of the original fields. It avoids shortcomings of the traditional concept, which made its application to the Earth's core rather problematic. In our models patterns of the convective motions are used originating from simulations under conditions which are realistic for the situation to be assumed in the Earth's core. The main result we expect from the proposed work is a contribution to understanding the time variations of the geomagnetic field and their connection with the fluid motions in the Earth's core.