INNER-CORE ANISOTROPY, ANOMALIES IN THE TIME-AVERAGED PALEOMAGNETIC FIELD, AND POLARITY TRANSITION PATHS

The diffusion of the dynamo-generated magnetic field into the electric ally 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 magnetizati on in the inner core which changes on diffusive timescales can provide a biasing field which could produce the observed anomalies in the tim e-averaged field and polarity reversals. The Earth's inner core exhibi ts an anisotropy in seismic velocities which can be explained by a pre ferred orientation of a polycrystalline aggregate of hexagonal dose-pa cked (hcp) iron, an elastically anisotropic phase. Room temperature an alogs of hcp iron also exhibit a strong anisotropy of magnetic suscept ibility, ranging from 15 to 40% anisotropy. At inner core conditions t he magnetic susceptibility of hcp iron is estimated to be between 10(- 4) and 10(-3) SI. We speculate here that the anisotropy in magnetic su sceptibility in the inner core could produce the observed anomalies in the time-averaged paleomagnetic field, polarity asymmetry, and recurr ing transitional virtual geomagnetic pole (VGP) positions.