Negative effect of turbulent convection on mean magnetic pressure
by
Petri Käpylä
→
Europe/Stockholm
122:026
122:026
Description
We investigate the effects of anisotropic stratified turbulent convection on the mean effective Lorentz force. Earlier studies with isotropically forced non-stratified and stratified turbulence have shown that the contribution of turbulence to the mean magnetic pressure is negative for mean magnetic fields that are smaller than the equipartition strength, so that the effective mean magnetic pressure that takes into account the turbulence effects, can be negative. Compared with earlier cases of forced turbulence, we find that the turbulence effect is stronger in turbulent convection with an imposed horizontal mean magnetic field due to the anisotropy of turbulence in the vertical direction. Mean-field modeling adapted to the present case indicates that the negative effective magnetic pressure leads to a large-scale instability which forms local flux concentrations. It is argued that those could be important for the formation of solar large-scale magnetic structures, e.g., sunspots. The current direct numerical simulations, however, do not form such flux concentrations in the parameter range studied here.