Space Climate 7 Meeting Abstract
Modelling solar and stellar activity driven by turbulent dynamo effects
Jörn Warnecke (Max-Planck-Institute for Solar System Research)
The magnetic field in the Sun undergoes a cyclic modulation with a reversal typically every 11 years due to a dynamo operating under the surface. Other solar-like stars with outer convective envelopes shows cyclic modulation of their magnetic activity, the level and cycle period being related to their rotation rate. This is suggestive of a common dynamo mechanism. Here we present results of 3D MHD convective dynamo simulations of slowly and rapidly rotating solar-type stars, where the interplay between convection and rotation self-consistently drives a large-scale magnetic field. With the help of the test-field method, we are able to measure the turbulent transport coefficients in these simulations and therefore get insights about the dynamo mechanism operating in them. It allows us to explain the weak dependency of the cycle period found in the moderate rotation regime using a Parker dynamo wave operating in our simulations. Furthermore, we find that the alpha effect becomes highly anisotropic for high rotation rates, which can explain the high degree of non-axisymmetry of magnetic field in observations and models of rapid rotating stars. Overall, the turbulent contributions to the electromagnetic force play an important role for dynamics and evolution of the large-scale magnetic field in all of our simulations. Stars spinning faster than the Sun are expected to also produce larger amount of magnetic helicity at their surfaces. On the Sun, magnetic helicity is essential for the release of energy leading to the eruption of plasma via coronal mass ejection and it though to play an important role in the heating process of the coronal plasma. Using MHD simulations of solar coronae we find a power law relation between the surface magnetic helicity and the temperature and activity of these coronae, suggesting an important role of magnetic helicity production in understanding rotational dependence of stellar activity.
Mode of presentation: oral (Need to be confirmed by the SOC)