Buoyant Magnetic Loops in a Global Dynamo Simulation of a Young Sun

Type Journal Article
Names Nicholas J. Nelson, Benjamin P. Brown, Allan Sacha Brun, Mark S. Miesch, Juri Toomre
Publication The Astrophysical Journal Letters
Volume 739
Issue 2
Pages L38
Date October 1, 2011
URL http://adsabs.harvard.edu/abs/2011ApJ...739L..38N
Library Catalog NASA ADS
Abstract The current dynamo paradigm for the Sun and Sun-like stars places the generation site for strong toroidal magnetic structures deep in the solar interior. Sunspots and starspots on Sun-like stars are believed to arise when sections of these magnetic structures become buoyantly unstable and rise from the deep interior to the photosphere. Here, we present the first three-dimensional global magnetohydrodynamic (MHD) simulation in which turbulent convection, stratification, and rotation combine to yield a dynamo that self-consistently generates buoyant magnetic loops. We simulate stellar convection and dynamo action in a spherical shell with solar stratification, but rotating three times faster than the current solar rate. Strong wreaths of toroidal magnetic field are realized by dynamo action in the convection zone. By turning to a dynamic Smagorinsky model for subgrid-scale turbulence, we here attain considerably reduced diffusion in our simulation. This permits the regions of strongest magnetic field in these wreaths to rise toward the top of the convection zone via a combination of magnetic buoyancy instabilities and advection by convective giant cells. Such a global simulation yielding buoyant loops represents a significant step forward in combining numerical models of dynamo action and flux emergence.
Tags Convection, Magnetohydrodynamics: MHD, SUN: ACTIVITY, SUN: INTERIOR, Stars: Interiors, stars: magnetic field
UW-Madison Astronomy Home