HR: 0800h
AN: GP21A-0005    [Abstracts]
TI: Dynamics of Inverse Magnetic Field Patches in Dynamo Simulations
AU: * Wicht, J
EM: wicht@linmpi.mpg.de
AF: Max-Planck Inst fu Aeronomie, Inst Geophysik, Max-Planck Strasse 2, Katlenburg, D 37191 Germany
AB: The magnetic field in dynamo simulations varies over a wide range of time scales reaching from short yearly variations to changes in reversal rates over several tens of million years. Here I concentrate on the dynamics of inverse field patches at the core-mantel boundary. They grow and vanish over periods of some hundred years which constitutes an important part of the secular variation on this time scale. Two regions can be distinguished. At higher Rayleigh numbers time-varying plumes rising from the inner core to the tangent cylinder produce inverse patches at higher latitudes. The fierce dynamics of these plumes is responsible for increased secular variation in this area. Inverse patches are also created around the equator even at very low Rayleigh numbers. While normal-polarity patches dominate the equatorial region of the geomagnetic field inverse patches prevail in typical dynamo simulations. However, when decreasing the Ekman number to low values inverse patches become less and less frequent resulting in a more realistic simulation of the geomagnetic field. The discovery of strong inverse magnetic field patches at the top of the Earth's core has stirred speculations whether the magnetic field might reverse within the next milleniums. The simulations suggest that inverse patches are a typical rather than special feature of the magnetic field. Their appearence does not allow prediction of field reversals.
DE: 1510 Dynamo: theories and simulations
DE: 1513 Geomagnetic excursions
DE: 1535 Reversals: process, timescale, magnetostratigraphy
DE: 1560 Time variations: secular and longer
DE: 1599 General or miscellaneous
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005