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| Paper: |
Theoretical Basis of Stellar Activity Cycles |
| Volume: |
154, Cool Stars, Stellar Systems and the Sun: Tenth Cambridge Workshop |
| Page: |
173 |
| Authors: |
Brandenburg, Axel |
| Abstract: |
Numerical simulations of hydromagnetic turbulence in the presence of shear and/or convection have given us new clues as to how the solar dynamo might work. Simulations suggest that there is significant large-scale magnetic field generation at the bottom of the convection zone, where the radial shear is largest. The nature of the dynamo in the simulations seems to be qualitatively similar to an alpha Omega-dynamo. However, the origin of the effective alpha in the simulations is not thermal convection, but magnetobuoyancy and magnetic shear instabilities. This results in a negative alpha-effect. The efficiency of the alpha-effect on the one hand, and losses on the other, should increase as the field strength increases. It is argued that this could lead to an increasing ratio between cycle and rotation frequency with increasing field strength, as is indicated by the stellar cycle data of Baliunas and collaborators. Furthermore, to explain the cycle data for active stars one has to invoke another, as yet unknown, type of magnetic instability for which both alpha and the flux loss are abruptly reduced above a certain field strength. However, details of this speculation are still unclear. |
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