Regensburg 2004 – scientific programme

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MA: Magnetismus

MA 19: Hauptvortrag Tilgner

MA 19.1: Invited Talk

Thursday, March 11, 2004, 09:30–10:00, H10

Magnetic field generation in planets and laboratory dynamos — •Andreas Tilgner — Institut für Geophysik, Universität Göttingen, Herzberger Landstr. 180, 37075 Göttingen

Most celestial bodies (the sun, most planets, stars and galaxies) generate a large scale magnetic field by converting mechanical into magnetic energy. In such a “dynamo process” electric currents are generated inside a moving conductor which in turn create a magnetic field. In commercial dynamos in use in cars or on bicycles, these currents flow inside especially designed coils. In the earth however, the currents responsible for the magnetic field flow in the liquid conductor (mostly iron) constituting the core, which is spherical, devoid of electric structure and acts like a massive short circuit. It was therefore disputed until the late 1950’s whether the earth is capable of dynamo action. Doubts have been removed on a theoretical basis and an experiment has demonstrated the dynamo effect on a laboratory scale with a flow qualitatively resembling the flow believed to exist in the core. Insights into the flow actually realized in the core may be gained from numerical simulations, whereas observations of the variations of the earth’s magnetic field allow to determine the velocity at the boundary between the core and the electrically insulating, solid mantle. We do not know yet what is driving the core flow. The most probable mechanism is convection, but the precession of the earth’s axis of rotation may also play a role.