Island geomagnetic observatories and upper mantle electric conductivity profiles

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The electrical conductivity profile of the Earth can be investigated by analyzing the observed magnetic and electric fields at the surface. Observations of the geomagnetic field are readily available from a worldwide network of ground-based geomagnetic observatories which provide data of high quality and of high resolution. However, simultaneous electric field measurements of comparable quality and quantity are not provided. Recently, a method to obtain 1-D electric conductivity profiles from geomagnetic observations alone has been suggested. This method is based on the observation of tippers, which relate the vertical and horizontal components of the observed geomagnetic field variations. Further, this method has been demonstrated to resolve 1-D conductivity profiles of the crust and upper mantle by exploiting the known lateral conductivity contrasts of seawater and bedrock near island observatories. With other methods, such conductivity profiles are difficult to obtain due to the logistical challenges associated with observations at sea.In this project, we will apply the recently suggested method to island observatories. For this purpose, we will select suitable observatories, calculate tippers from the geomagnetic data, and assemble detailed models of the island bathymetry. Finally, we will invert these tippers for local 1-D conductivity profiles of the crust and upper mantle. Such conductivity profiles contain valuable information on chemical and thermal transport properties, but also will help to improve our understanding of the measured surface magnetic field which results from a variety of sources. These sources are difficult to separate, and this research project will help to extract the signal of the induced sources in the upper mantle. In consequence, this research project may as well contribute to our knowledge of the electric current systems in the ionosphere and magnetosphere and facilitate the joint interpretation of satellite and ground based geomagnetic observations.