Mean-field analysis on large-scale magnetic fields at high Reynolds numbers
arXiv:2207.01639 · doi:10.3847/1538-4357/ac7e43
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.
arXiv comment17 pages, 20 figures, Accepted for publication in ApJ
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- Evolution of solar and stellar dynamo theory
- Mean field models of flux transport dynamo and meridional circulation in the Sun and stars
- Turbulent processes and mean-field dynamo
- A Babcock-Leighton dynamo model of the Sun incorporating toroidal flux loss and the helioseismically-inferred meridional flow