Paper (*cross-listing*): physics/0601011
Date: Tue, 3 Jan 2006 15:11:29 GMT (136kb)

Title: A paradigmatic model of Earth's magnetic field reversals

Authors: F. Stefani, G. Gerbeth, U. Guenther

Comments: 7 pages, 6 figures, submitted to Magnetohydrodynamics

Subj-class: Geophysics; Plasma Physics
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The irregular polarity reversals of the Earth's magnetic field have attracted
much interest during the last decades. Despite the fact that recent numerical
simulations of the geodynamo have shown nice polarity transitions, the very
reason and the basic mechanism of reversals are far from being understood.
Using a paradigmatic mean-field dynamo model with a spherically symmetric
helical turbulence parameter alpha we attribute the essential features of
reversals to the magnetic field dynamics in the vicinity of an exceptional
point of the spectrum of the non-selfadjoint dynamo operator. At such
exceptional (branch) points of square root type two real eigenvalues coalesce
and continue as a complex conjugated pair of eigenvalues. Special focus is laid
on the comparison of numerically computed time series with paleomagnetic
observations. It is shown that the considered dynamo model with high
supercriticality can explain the observed time scale and the asymmetric shape
of reversals with a slow decay and a fast field recovery.

\\ ( http://arXiv.org/abs/physics/0601011 , 136kb)