PREPRINT
5B80989D-E87B-4E16-A71A-A3FD314F1816

Mean-field analysis on large-scale magnetic fields at high Reynolds numbers

Ryota Shimada, Hideyuki Hotta, Takaaki Yokoyama
arXiv:2207.01639

Submitted on 4 July 2022

Abstract

Solar magnetic fields comprise an 11-year activity cycle, represented by the number of sunspots. The maintenance of such a solar magnetic field can be attributed to fluid motion in the convection zone, i.e. a dynamo. This study conducts the mean-field analyses of the global solar dynamo simulation presented by Hotta et al. (2016). Although the study succeeds in producing coherent large-scale magnetic fields at high Reynolds numbers, the detailed physics of the maintenance of this field have not been fully understood. This study extracts the alpha-tensor and the turbulent magnetic diffusivity tensor through mean-field analyses. The turbulent magnetic diffusivity exhibits a significant decrease towards high Reynolds numbers. The decrease in the turbulent magnetic diffusivity suppresses the energy conversion of large-scale field to small-scale field. This implies that the decrease in the turbulent magnetic diffusivity contributes to the maintenance of a large-scale magnetic field at high Reynolds numbers. A significant downward turbulent pumping is observed; it is enhanced in the weak phase of the large-scale field. This study proposes a cyclic reversal process of a large-scale field which is dominantly driven by the alpha-effect and is possibly triggered by downward pumping.

Preprint

Comment: 17 pages, 20 figures, Accepted for publication in ApJ

Subject: Astrophysics - Solar and Stellar Astrophysics

URL: https://arxiv.org/abs/2207.01639