PERSISTENT MAGNETIC WREATHS IN A RAPIDLY ROTATING SUN

By Benjamin P. Brown, M. Browning, A. Brun, Mark S. Miesch, J. Toomre. 2010

194 citations recorded by the source corpus.

When our Sun was young it rotated much more rapidly than now. Observations of young, rapidly rotating stars indicate that many possess substantial magnetic activity and strong axisymmetric magnetic fields. We conduct simulations of dynamo action in rapidly rotating suns with the three-dimensional magnetohydrodynamic anelastic spherical harmonic (ASH) code to explore the complex coupling between rotation, convection, and magnetism. Here, we study dynamo action realized in the bulk of the convection zone for a system rotating at 3 times the current solar rotation rate. We find that substantial organized global-scale magnetic fields are achieved by dynamo action in this system. Striking wreaths of magnetism are built in the midst of the convection zone, coexisting with the turbulent convection. This is a surprise, for it has been widely believed that such magnetic structures should be disrupted by magnetic buoyancy or turbulent pumping. Thus, many solar dynamo theories have suggested that a tachocline of penetration and shear at the base of the convection zone is a crucial ingredient for organized dynamo action, whereas these simulations do not include such tachoclines. We examine how these persistent magnetic wreaths are maintained by dynamo processes and explore whether a classical mean-field α-effect explains the regeneration of poloidal field. We find that the global-scale toroidal magnetic fields are maintained by an Ω-effect arising from the differential rotation, while the global-scale poloidal fields arise from turbulent correlations between the convective flows and magnetic fields. These correlations are not well represented by an α-effect that is based on the kinetic and magnetic helicities.

Subfields: Astronomy and Astrophysics, Computational Mechanics, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/5bfe0e3760e13b1fb9b759cc48c73303ccbff829

How researchers see this paper

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In Astronomy and Astrophysics

1. Paul Charbonneau
2. M. Browning
3. Mark S. Miesch
4. A. Brun
5. J. Toomre
6. A. Reiners
7. Benjamin P. Brown
8. W. Arnett

In Computational Mechanics

1. Paul Charbonneau
2. M. Browning
3. A. Brun
4. J. Toomre
5. Mark S. Miesch
6. Benjamin P. Brown
7. T. Gastine
8. N. Wright

In Molecular Biology

1. Paul Charbonneau
2. Mark S. Miesch
3. M. Browning
4. J. Toomre
5. A. Brun
6. Benjamin P. Brown
7. A. Reiners
8. W. Arnett

Citations in the corpus

• A BCool magnetic snapshot survey of solar-type stars (2013, background): “…that operates throughout the whole convection zone, a so-called distributed dynamo whose existence is supported by the observational evidence accumulated throughout the last decade (i.e. Donati et al. 2003; Petit et al. 2004; Marsden et al. 2006), and detailed numerical models (Brown et al. 2010).”
• MAGNETIC CYCLES IN A CONVECTIVE DYNAMO SIMULATION OF A YOUNG SOLAR-TYPE STAR (2011, methodology): “In Paper I (Brown et al. 2010) we studied dynamo action in a star rotating three times faster than our current Sun and found that global-scale magnetic structures can arise naturally in the midst of the stellar convection zone.”
• The stellar rotation–activity relationship in fully convective M dwarfs (2018, background): “…simulations have found that differential rotation within the convection zone of stars can generate large-scale toroidal magnetic fields through the effect without the need for a tachocline (e.g. Muñoz-Jaramillo, Nandy & Martens 2009; Brown et al. 2010; Nelson et al. 2013; Yadav et al. 2015, 2016).”
• Solar Dynamo Theory (2014, methodology): “By contrast, the simulations of Brown et al. (2010) achieved the buildup of large-scale magnetic fields concentrated within the low-latitudes portions of the convecting layers, but again without reversals of magnetic polarity. www.annualreviews.org • Solar Dynamo Theory 257 A nn u.”
• MAGNETIC WREATHS AND CYCLES IN CONVECTIVE DYNAMOS (2012, methodology): “Magnetic Topology Figure 1 shows snapshots of the turbulent convection and the wreaths for cases D3, D3a, and D3b at mid- Table 2 Volume-Averaged Energy Densities and Differential Rotation Rates Case Total ME TME PME FME Total KE DRKE MCKE FKE ∆Ωr ∆Ωθ D3 0.68 (9”
• TOWARD REALISTIC PROGENITORS OF CORE-COLLAPSE SUPERNOVAE (2011, methodology): “…et al. 2006; Moćak et al. 2008, 2009, 2010), and on turbulent MHD with rotation (e.g., M dwarf simulations by Browning 2008), as well as extensive work on the Sun with the ASH code (e.g., Brown et al. 2010) and on stellar atmospheres pioneered by Nordlund and Stein (e.g., Nordlund et al. 2009).”