Storage of Magnetic Flux in the Solar Convective Overshoot Region
Abstract
The stability of magnetic fields in the solar interior is of critical importance for dynamo models. Instabilities induced by external flows are relevant for the storage of magnetic field in the stably stratified lower convective overshoot region. We have investigated the effects of finite perturbations and external flows on the stability and dynamics of thin magnetic flux tubes in mechanical equilibrium in the overshoot region. We have used a model convection zone based on the non-local mixing length approximation. Numerical simulations have shown that the friction-induced flux tube instability occurs already for field strengths well below the critical value for the onset of Parker instability, though with significantly longer growth times. Above a certain amplitude of the radial perturbation, nonlinear effects introduced by the external stratification become sufficient to affect the further growth of the instability. We have carried out a systematic parameter study with flux tubes subject to external radial flows. We have obtained ranges for the maximum speed and the duration of the flow, which allow for the storage of magnetic flux tubes with near-equipartition field strengths in the overshoot region, for times comparable with the dynamo amplification time.
- Publication:
-
European Solar Physics Meeting
- Pub Date:
- September 2008
- Bibcode:
- 2008ESPM...12..3.3I