Volume 530, June 2011
|Number of page(s)||6|
|Published online||26 May 2011|
Oscillatory dynamos and their induction mechanisms
MAG (ENS/IPGP), LRA, École Normale Supérieure, 24 rue Lhomond, 75252 Paris Cedex 05, France
2 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
Received: 20 December 2010
Accepted: 5 April 2011
Context. Large-scale magnetic fields resulting from hydromagnetic dynamo action may differ substantially in their time dependence. Cyclic field variations, characteristic for the solar magnetic field, are often explained by an important Ω-effect, i.e., by the stretching of field lines because of strong differential rotation.
Aims. The dynamo mechanism of a convective, oscillatory dynamo model is investigated.
Methods. We solve the MHD-equations for a conducting Boussinesq fluid in a rotating spherical shell. We computed the dynamo coefficients for the resulting oscillatory model with the help of the so-called test-field method. Subsequently, these coefficients were used in a mean-field calculation to explore the underlying dynamo mechanism.
Results. The oscillatory dynamo model we consider is an α2Ω one. Although the fairly strong differential rotation of this model influences the magnetic field, the Ω-effect alone is not responsible for its cyclic time variation. If the Ω-effect is suppressed, the resulting α2-dynamo remains oscillatory. Surprisingly, the corresponding αΩ-dynamo leads to a non-oscillatory magnetic field.
Conclusions. The assumption of an αΩ-mechanism does not explain the occurrence of magnetic cycles satisfactorily.
Key words: dynamo / magnetohydrodynamics (MHD) / magnetic fields / Sun: dynamo
© ESO, 2011
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