Large-scale flows and magnetic fields in solar-like stars from global simulation with and without tachocline

Thursday, 18 December 2014
Gustavo Guerrero, UFMG Federal University of Minas Gerais, Belo Horizonte, Brazil, Alexander G Kosovichev, New Jersey Institute of Technology, Edison, NJ, United States, Piotr K Smolarkiewicz, European Centre for Medium-Range Weather Forecasts, Wokingham, United Kingdom and Elisabete M de Gouveia Dal Pino, IAG Institute of Astronomy, Geophysics and Atmospheric Sciences, Sao Paulo, Brazil
The large-scale flows patterns like differential rotation and meridional circulation as well as the mean-field dynamo action in the Sun and solar-like stars are thought to have their origin in helical turbulent motions in the stellar convection zones. In this work we will present recent results of HD and MHD global simulations of stars whose stratification resemble that of the solar interior. The simulations are performed with the EULAG code (Smolarkiewicz et al. 2001). They include implicit modeling of the large-eddy contribution from the turbulent scales to the resolved scales, thus, allowing higher turbulent levels (e.g., Guerrero et al. 2013). In the HD regime, the value of the Rossby (Ro) number defines large-scale flow patterns. Large values of Ro result in an anti-solar differential rotation and a meridional circulation consistent with a single circulation cell per hemisphere. Lower values of Ro result in a solar-type differential rotation and a meridional flow with multiple cells in radius and latitude. Due to the low dissipation of the numerical scheme, the models are also able to reproduce the tachocline and sustain it over a longer time scale. In the MHD regime, both solutions are still allowed, however, the shift from anti-solar to the solar-like rotation happens at a larger value or Ro. A wide range of dynamo solutions is obtained for the magnetic field, including steady and oscillating modes (see e.g., Fig. 1). We also compare models with and without a stable stratified layer at the bottom of the convection zone. We notice that the presence of a naturally developed tachocline plays an important role in the dynamo solution, modifying the morphology of the magnetic field, the cycles period and influencing the large-scale flows.


Smolarkiewicz, P. K., Margolin, L. G., & Wyszogrodzki, A. A. 2001, JAtS, 58, 349;

Guerrero, G., Smolarkiewicz, P. K., Kosovichev, A.K., Mansour, N.N. 2013, ApJ, 779, 176.