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Exploring an Electrically Conducting Lowermost Mantle as a Mechanism for the Non-Uniform Geomagnetic Secular Variation over the Surface of the Earth

The secular variation of the geomagnetic refers to the changes of the Earth’s magnetic field on short time scales (annual to decadal). The rate of secular variation has been found to be not constant over the surface of the Earth, specifically in the Pacific hemisphere there is very little secular variation at all. One classical explanation of requires parts of the lower mantle to have a very high electrical conductivity. This high conductivity would screen out any quickly time varying components of the magnetic field, reducing the observed secular variation. Unfortunately, for the screening effect to work an unrealistically high conductance is required in the mantle, which is incompatible with constraints placed by the angular momentum budget of the Earth.

The classical electromagnetic screening effect is a linear effect which filters a time varying magnetic field produced by the Earth’s core. This does not take into account the fact that an electrically conducting angle can interact with the flows in the Earth’s core and brake the flows which generated secular variation.
I report on progress to incorporate a conducting mantle of non-uniform electrical conductivity into the mMoSST numerical dynamo model to study whether this can help explain the heterogeneous secular variation we observe over the surface of the Earth.