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3 Publications

A paradigmatic model of Earth's magnetic field reversals

Stefani, F.; Gerbeth, G.; Günther, U.

The phenomenon of sudden and irregular reversals of the Earth's magnetic field has attracted much interest in the last decades. It is known that the mean reversal rate varies from approximately zero in the Permian and Cretaceous supercrons to approximately 5 per Myr in the present. There is some observational evidence for the facts that the reversals are asymmetric in time and that the overall distribution of the field intensity has a bimodal behaviour. In an attempt to explain these features in a paradigmatic model we investigate a mean-field dynamo model of the alpha^2 type. Field saturation is guaranteed by alpha-quenching, and the influence of noise is taken into account. In order to keep the model simple and to allow for very long simulations, we choose the helical turbulence parameter alpha as spherically symmetric. We show that reversals occur in the vicinity of so-called exceptional points of the spectrum of the dynamo operator, where two real eigenvalues coalesce and continue as a pair of complex conjugate eigenvalues. We describe the reversal mechanism, and all the above mentioned features, in terms of a self-accelerating field decay, followed by the rapid recovery of the field with opposite polarity. We point out that the reversal mechanism can be attributed to the square-root character of exceptional points in the spectrum. Hence it is not restricted to our particular model but should be identifiable also in more realistic models of the Earth dynamo.

  • Lecture (Conference)
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on Fundamental and Applied MHD, 27.06.-01.07.2005, Jurmala, Latvia
    Proceedings 1(2005), 97-100
  • Magnetohydrodynamics 42(2006)2/3, 123-130
    ISSN: 0024-998X

Permalink: https://www.hzdr.de/publications/Publ-7358
Publ.-Id: 7358