Use of geomagnetic data for studies on the Earth's deep interior

The methods are described which are in use for the study of the deep interior of the Earth and the present knowledge of the conductivity profile of the mantle. Also motions of the top of the core, motions inside the core and the geodynamo, and the core-mantle coupling including the exchanges of heat and angular momentum with effects on the Earth's rotation are discussed. The importance of long time series of geomagnetic data with high absolute accuracy from different parts of the world is stressed, as well as the importance of satellite surveys. The knowledge of the geomagnetic secular variation based on observatory data is found still insufficient and needing improvement for the modeling of the conductivity of the deep mantle, the diffusion at the core-mantle boundary and the fluid velocities at the core-mantle boundary. The main field geomagnetism has reached the point where accurate global vector data extending over significant time span is required for significant advances in SEDI.