Regional electromagnetic probing of the Earth mantle by ionospheric sources

Advisor: Jakub Velímský (DG MFF CUNI)

Funding: Base scholarship supplemented from a national grant and ESA contract for the first two years (net income 20 000 CZK/month). Extension of the supplement beyond that is subject to availability of funds.



The electrical conductivity is an important geophysical parameter connected to the thermal, chemical, and mineralogical state of the Earth's mantle. A traditional technique to study the distribution of electrical conductivity in deep regions of the Earth is the electromagnetic induction (EMI) method. On the global planetary scale, the natural sources of electromagnetic energy with the largest potential to probe the deep Earth structure are present in the magnetosphere and ionosphere. The tidal signals generated by the interaction of ocean flows with the geomagnetic field have been also used recently. With the recent developments of modern forward and inverse modelling methods, the increase of the parallelized supercomputing power, and with the availability of accurate data from the Swarm satellite mission by the European Space Agency, and from the global ground geomagnetic observatory network, the 3-D global inversions for mantle conductivity structures are within our reach.

Geomagnetic solar daily variations, the Sq signals, are used in electromagnetic induction studies to estimate the electrical conductivity of the Earth's upper mantle. Traditionally, Sq induction studies employ the observatory magnetic data from a few quiet days, separate them into external (due to the ionospheric Sq current system) and internal (due to induced counterpart in the Earth) parts, and interpret the latter part in terms of the upper mantle electrical conductivity. Satellite magnetic observations by CHAMP and Swarm helped to make a finer coverage of magnetic data. Although the spatiotemporal sampling of Sq signals by satellites, is limited by a tradeoff between the spatial and temporal resolution, it is sufficient to resolve lateral variations in the upper-mantle conductivity. However, a key issue of satellite Sq observations is that the primary magnetic field due to ionospheric currents and the secondary magnetic field induced by the currents in the Earth are observed at satellite altitudes as an internal magnetic field since magnetic satellites fly above the ionosphere. Hence, the ground observatory data must be included to perform the separation of Sq satellite signals into external and internal parts A strongly uneven distribution of magnetic observatories consequently reduces a fine temporal and spatial resolution of satellite magnetic data.

The candidate will familiarize himself with the existing tools for forward and inverse 3-D modelling of the EMI problem in the global domain. He will modify and apply these tools on regional scale in the areas with good ground observatory coverage. Ultimately, he will seek an answer to the following question: Can we constrain the 3-D upper mantle conductivity from ionospheric variations in regions with dense observatory coverage, and how can the satellite data contribute to such analysis despite their lack of external/internal field separation ability?