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Title: BUOYANT MAGNETIC LOOPS IN A GLOBAL DYNAMO SIMULATION OF A YOUNG SUN

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.

Authors:
;  [1];  [2];  [3];  [4]
  1. JILA and Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO 80309-0440 (United States)
  2. Department of Astronomy and Center for Magnetic Self-Organization (CSMO) in Laboratory and Astrophysical Plasmas, University of Wisconsin, Madison, WI 53706-1582 (United States)
  3. Laboratoire AIM Paris-Saclay, CEA/Irfu Universite Paris-Diderot CNRS/INSU, 91191 Gif-sur-Yvette (France)
  4. High Altitude Observatory, NCAR, Boulder, CO 80307-3000 (United States)
Publication Date:
OSTI Identifier:
21565440
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal Letters
Additional Journal Information:
Journal Volume: 739; Journal Issue: 2; Other Information: DOI: 10.1088/2041-8205/739/2/L38; Journal ID: ISSN 2041-8205
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CONVECTION; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; PHOTOSPHERE; SIMULATION; STRATIFICATION; SUN; SUNSPOTS; THREE-DIMENSIONAL CALCULATIONS; TURBULENCE; ATMOSPHERES; ENERGY TRANSFER; FLUID MECHANICS; HEAT TRANSFER; HYDRODYNAMICS; MAIN SEQUENCE STARS; MASS TRANSFER; MECHANICS; SOLAR ACTIVITY; SOLAR ATMOSPHERE; STARS; STARSPOTS; STELLAR ACTIVITY; STELLAR ATMOSPHERES

Citation Formats

Nelson, Nicholas J., Toomre, Juri, Brown, Benjamin P., Brun, Allan Sacha, and Miesch, Mark S. BUOYANT MAGNETIC LOOPS IN A GLOBAL DYNAMO SIMULATION OF A YOUNG SUN. United States: N. p., 2011. Web. doi:10.1088/2041-8205/739/2/L38.
Nelson, Nicholas J., Toomre, Juri, Brown, Benjamin P., Brun, Allan Sacha, & Miesch, Mark S. BUOYANT MAGNETIC LOOPS IN A GLOBAL DYNAMO SIMULATION OF A YOUNG SUN. United States. doi:10.1088/2041-8205/739/2/L38.
Nelson, Nicholas J., Toomre, Juri, Brown, Benjamin P., Brun, Allan Sacha, and Miesch, Mark S. Sat . "BUOYANT MAGNETIC LOOPS IN A GLOBAL DYNAMO SIMULATION OF A YOUNG SUN". United States. doi:10.1088/2041-8205/739/2/L38.
@article{osti_21565440,
title = {BUOYANT MAGNETIC LOOPS IN A GLOBAL DYNAMO SIMULATION OF A YOUNG SUN},
author = {Nelson, Nicholas J. and Toomre, Juri and Brown, Benjamin P. and Brun, Allan Sacha and Miesch, Mark S.},
abstractNote = {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.},
doi = {10.1088/2041-8205/739/2/L38},
journal = {Astrophysical Journal Letters},
issn = {2041-8205},
number = 2,
volume = 739,
place = {United States},
year = {2011},
month = {10}
}