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Inner core anisotropy, anomalies in the time-averaged paleomagnetic field, and polarity transition paths |
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| Authors: | Bradford M Clement Lars Stixrude |
| Institution: | aDepartment of Geology, Florida International University, Miami, FL 33199,USA bInstitut für Geophysik, Herzberger Landstrasse 180, Universität Göttingen, 37075 Göttingen ,Germany |
| Abstract: | The diffusion of the dynamo-generated magnetic field into the electrically conducting inner core of the Earth may provide an explanation for several problematic aspects of long-term geomagnetic field behavior. We present a simple model which illustrates how an induced magnetization in the inner core which changes on diffusive timescales can provide a biasing field which could produce the observed anomalies in the time-averaged field and polarity reversals. The Earth's inner core exhibits an anisotropy in seismic velocities which can be explained by a preferred orientation of a polycrystalline aggregate of hexagonal close-packed (hcp) iron, an elastically anisotropic phase. Room temperature analogs of hcp iron also exhibit a strong anisotropy of magnetic susceptibility, ranging from 15 to 40% anisotropy. At inner core conditions the magnetic susceptibility of hcp iron is estimated to be between 10?4 and 10?3 SI. We speculate here that the anisotropy in magnetic susceptibility in the inner core could produce the observed anomalies in the time-averaged paleomagnetic field, polarity asymmetry, and recurring transitional virtual geomagnetic pole (VGP) positions. |
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