The Rossby-number Dependence of Large-scale Dynamo in Solar-like Strongly-stratified Convection
Aichi University of Education
Natural Sciences (Astrophysics and Astrononmy)
In Masada & Sano (2016), we reported the successful simulation of spontaneous formation of surface magnetic structures from a large-scale dynamo in strongly-stratified plane-layer convection. The large-scale dynamo observed in our model had physical properties similar to those in earlier weakly- stratified convective dynamo simulations (Kapyla et al. 2013; Masada & Sano 2014a,b), suggesting that the α^2-type mechanism is responsible for it. In this talk, we will present our recent results on the Rossby number (Ro) dependence of the large-scale dynamo in the strongly-stratified convection. From our study, we found that the critical Rossby number that separates the success and failure of the dynamo is in the range 0.02 < Ro < 0.04, which is compatible with the recent global convective dynamo simulation of solar-like stars by Kapyla et al. (2013). We also find that the Ro-dependence of the large-scale dynamo can be reproduced by the mean-field α^2-type dynamo model constructed with using turbulent velocity profiles extracted from the DNS results. We finally discuss the reason why the model with the higher Rossby number fails to sustain the dynamo with focusing on the profiles of the turbulent transport coefficients.
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