Turbulent magnetic helicity fluxes in solar convective zone
Abstract
Combined action of helical motions of plasma (the kinetic α effect) and non-uniform (differential) rotation is a key dynamo mechanism of solar and galactic large-scale magnetic fields. Dynamics of magnetic helicity of small-scale fields is a crucial mechanism in a non-linear dynamo saturation where turbulent magnetic helicity fluxes allow to avoid catastrophic quenching of the α effect. The convective zone of the Sun and solar-like stars, as well as galactic discs, are the source for production of turbulent magnetic helicity fluxes. In the framework of the mean-field approach and the spectral τ approximation, we derive turbulent magnetic helicity fluxes using the Coulomb gauge in a density-stratified turbulence. The turbulent magnetic helicity fluxes include non-gradient and gradient contributions. The non-gradient magnetic helicity flux is proportional to a non-linear effective velocity (which vanishes in the absence of the density stratification) multiplied by small-scale magnetic helicity, while the gradient contributions describe turbulent magnetic diffusion of the small-scale magnetic helicity. In addition, the turbulent magnetic helicity fluxes contain source terms proportional to the kinetic α effect or its gradients, and also contributions caused by the large-scale shear (solar differential rotation). We have demonstrated that the turbulent magnetic helicity fluxes due to the kinetic α effect and its radial derivative in combination with the non-linear magnetic diffusion of the small-scale magnetic helicity are dominant in the solar convective zone.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 2022
- DOI:
- 10.1093/mnras/stac2141
- arXiv:
- arXiv:2206.14152
- Bibcode:
- 2022MNRAS.515.5437K
- Keywords:
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- MHD;
- Sun: dynamo;
- Sun: interior;
- Sun: magnetic fields;
- turbulence;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 13 pages, 9 figures, revised