Monday june 4th 2018
Antoine Strugarek, CEA Paris Saclay

Title: Simulations of the magnetic cycles of the Sun and solar-type stars

The Sun sustains its large-scale magnetic field thanks to its internal turbulent motions through a so-called dynamo effect. Global simulations of the convective dynamo of the Sun and solar-type stars have exhibited in the past decade a rich variety of magnetic self-organization, from small-scale turbulent fields; stable magnetic structures; to periodically reversing large-scale magnetic fields. In the cyclic cases, though, the physical ingredients setting the cycle period still eluded our understanding.

After introducing observational constraints on solar and stellar magnetism, I will first give a brief tour of the present status of non-linear dynamo simulations in deep stellar convection zones, with a particular focus on results obtained using implicit large eddy simulations (ILES) for solar-like, cyclic, turbulent dynamos. I will put a particular emphasis on the numerical methods used to simulate the interior of stars, which are in a turbulent regime inaccessible to both experiments and numerical simulations as of today. I will then present a series of 3D global simulations performed with the EULAG code where the period of the simulated magnetic cycle systematically varies with the rotation rate and luminosity of the modelled star. The dynamo acting in these simulations is fundamentally non-linear, where the Lorentz force feedback on the mean flows plays a major role in the dynamo loop. These results shed a new light on non-linear dynamo processes possibly acting inside solar-like stars.

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