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Science 26 September 2008:
Vol. 321. no. 5897, p. 1800
DOI: 10.1126/science.1159777
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Brevia

Magnetic Source Separation in Earth's Outer Core

Kenneth A. Hoffman1,2* and Brad S. Singer2

We present evidence that the source of Earth's axial dipole field is largely independent from the sources responsible for the rest of the geomagnetic field, the so-called nonaxial dipole (NAD) field. Support for this claim comes from correlations between the structure of the historic field and the behavior of the paleomagnetic field recorded in precisely dated lavas at those times when the axial dipole was especially weak or nearly absent. It is argued that a "stratification" of magnetic sources exists in the fluid core such that the axial dipole is the only observed field component that is nearly immune from the influence exerted by the lowermost mantle. It follows that subsequent work on spherical harmonic-based field descriptions may now incorporate an understanding of a dichotomy of spatial-temporal dynamo processes.

1 Physics Department, California Polytechnic State University, San Luis Obispo, CA 93407, USA.
2 Department of Geology and Geophysics, University of Wisconsin-Madison, Madison, WI 53706, USA.

* To whom correspondence should be addressed. E-mail: khoffman{at}calpoly.edu

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Science. ISSN 0036-8075 (print), 1095-9203 (online)