We study magnetic field evolution in flows with fluctuating in time governing parameters in electrically conducting fluid. We use a standard mean-field approach to derive equations for large-scale magnetic field for the fluctuating... more
We study magnetic field evolution in flows with fluctuating in time governing parameters in electrically conducting fluid. We use a standard mean-field approach to derive equations for large-scale magnetic field for the fluctuating Arnold-Beltrami-Childress ABC flow as well as for the fluctuating Roberts flow. The derived mean-field dynamo equations have growing solutions with growth rate of the large-scale magnetic field which is not controlled by molecular magnetic diffusivity. Our study confirms the Zeldovich idea that the nonstation-arity of the fluid flow may remove the obstacle in the large-scale dynamo action of classic stationary flows.
In the presence of strong density stratification, hydromagnetic turbulence attains qualitatively new properties: the formation of magnetic flux concentrations. We review here the theoretical foundations of this mechanism in terms of what... more
In the presence of strong density stratification, hydromagnetic turbulence attains qualitatively new properties: the formation of magnetic flux concentrations. We review here the theoretical foundations of this mechanism in terms of what is now called the negative effective magnetic pressure instability. We also present direct numerical simulations of forced turbulence in strongly stratified layers and discuss the qualitative and quantitative similarities with corresponding mean-field simulations. Finally, the relevance to sunspot formation is discussed.
We demonstrate that the inclusion of the helicity flux in the magnetic helicity balance in the nonlinear stage of galac-tic dynamo action results in a radical change in the magnetic field dynamics. The equilibrium value of the large-scale... more
We demonstrate that the inclusion of the helicity flux in the magnetic helicity balance in the nonlinear stage of galac-tic dynamo action results in a radical change in the magnetic field dynamics. The equilibrium value of the large-scale magnetic field is then approximately the equipartition level. This is in contrast to the situation without the flux of helicity, when the magnetic helicity is conserved locally, which leads to substantially subequipartition values for the equilibrium large-scale magnetic field.
