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

Teed, R. J. and Proctor, M. R. E. (2017) Quasi-cyclic behaviour in non-linear simulations of the shear dynamo. Monthly Notices of the Royal Astronomical Society, 467(4), pp. 4858-4864. (doi: 10.1093/mnras/stx421)

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.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Teed, Dr Robert
• Authors: Teed, R. J., and Proctor, M. R. E.
• College/School: College of Science and Engineering > School of Mathematics and Statistics > Mathematics
• Journal Name: Monthly Notices of the Royal Astronomical Society
• Publisher: Oxford University Press
• ISSN: 0035-8711
• ISSN (Online): 1365-2966
• Published Online: 17 February 2017
• Copyright Holders: Copyright © 2017 The Authors
• First Published: First published in Monthly Notices of the Royal Astronomical Society 467(4):4858-4864
• Publisher Policy: Reproduced in accordance with the copyright policy of the publisher