Satellite measurements required for deep-earth geophysics

Three major scientific issues arising within the less accessible, deeper parts of the earth can be phrased as the following questions: (1) What is the vertical profile of horizontally averaged electrical conductivity in the lower mantle (below the depths available to magnetotelluric sounding); (2) What is the intensity and pattern of the geomagnetic field (especially the vertical component) at the core-mantle boundary; and (3) What are the patterns of horizontal fluid motion in the outer core just beneath the core-mantle boundary. Answers to the first two questions are prerequisite to the thorough understanding of the geodynamo, that can only be started with an answer to question 3. Yet traditionally mantle conductivity is ignored in the downward extrapolation of surface magnetic measurements to the core-mantle boundary. The questions and some possible answers are briefly discussed.