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Quasi-cyclic behaviour in non-linear simulations of the shear dynamo

Published version
Peer-reviewed

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Type

Article

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Authors

Teed, RJ 
Proctor, MRE 

Abstract

The solar magnetic field displays features on a wide range of length-scales including spatial and temporal coherence on scales considerably larger than the chaotic convection that generates the field. Explaining how the Sun generates and sustains such large-scale magnetic field has been a major challenge of dynamo theory for many decades. Traditionally, the ‘mean-field’ approach, utilizing the well-known α-effect, has been used to explain the generation of large-scale field from small-scale turbulence. However, with the advent of increasingly high-resolution computer simulations there is doubt as to whether the mean-field method is applicable under solar conditions. Models such as the ‘shear dynamo’ provide an alternative mechanism for the generation of large-scale field. In recent work, we showed that while coherent magnetic field was possible under kinematic conditions (where the kinetic energy is far greater than magnetic energy), the saturated state typically displayed a destruction of large-scale field and a transition to a small-scale state. In this paper, we report that the quenching of large-scale field in this way is not the only regime possible in the saturated state of this model. Across a range of simulations, we find a quasi-cyclic behaviour where a large-scale field is preserved and oscillates between two preferred length-scales. In this regime, the kinetic and magnetic energies can be of a similar order of magnitude. These results demonstrate that there is mileage in the shear dynamo as a model for the solar dynamo.

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Keywords

dynamo, magnetic fields, MHD, methods: numerical

Journal Title

Monthly Notices of the Royal Astronomical Society

Conference Name

Journal ISSN

0035-8711
1365-2966

Volume Title

467

Publisher

Oxford University Press
Sponsorship
Science and Technology Facilities Council (ST/L000636/1)
Science and Technology Facilities Council (ST/P000673/1)
This work was supported by the Science and Technology Facilities Council, grant ST/L000636/1.