Diffusion of the geomagnetic secular variation through the heterogeneous mantle

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The electrical conductivity in the lower mantle is poorly constrained by induction studies using external sources (with periods up to the solar cycle variation of 11 years). Therefore the present study tries to complement these results by using in addition the geomagnetic secular variation as an internal source. However, in this approach we are faced with the problem that the temporal and spatial structure of the source is unknown and has to be replaced by a statistical description. The proposal focuses on two topics.Firstly: Assuming a radially symmetric conductivity distribu- tion with a well-constrained upper part and a sparsely para- metrized lower part, we try to estimate the unknown parameters in the statistical description of the source. The results of induction studies with external sources are used as con- straints.This work can be considered as an extension of the classical approach of Mc Donald (1957).Secondly: It is often argued that lateral variations of deep mantle electrical conductivity will find their manifestation in the geomagnetic field at the Earth`s surface, e.g. by preferred VGP paths or by the different pattern of the secular variation in the Atlantic and Pacific hemisphere. Taking lateral variations of mantle conductivity into account by a nonuniform spherical thin sheet, we develop a code for numerical modelling and investigate possible impacts of deep mantle heterogeneity onto the secular variation pattern at the surface of the Earth.