科研之友
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摘要
Numerical calculations of dynamo action in a rapidly rotating spherical shell are performed. We report cases of multistability, i.e., situations for which several solutions with different kinetic energies and different abilities to produce self-sustained dynamos are observed for a given set of driving parameters. We then introduce a modulation (in time) of the thermal forcing. These calculations are carried out for parameters in the vicinity of the ones used in the bistability cases. It is indeed likely that the modulation will have a stronger effect in these regions of the parameter space. In all our simulations, the convective flow roughly follows the modulation. However, interesting effects develop in a number of cases. If the imposed modulation is large enough to imply a crossing of the dynamo threshold, magnetohydrodynamic interactions are able to change the dynamics of the system with different hydro and magnetic modes being selected during each oscillation, leading to an overall very complex behavior of the system. Applying a noise-like modulation of relatively low amplitude and of high frequency (compared to the inverse magnetic diffusion time), we observe sudden bursts or drops in the magnetic activity. These events are associated with sudden and dramatic changes in the flow geometry.
- 出版日期2010
