Dynamo Action in the Solar Convection Zone and Tachocline: Pumping and Organization of Toroidal Fields

By M. Browning, Mark S. Miesch, A. Brun, J. Toomre. 2006

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We present the first results from three-dimensional spherical shell simulations of magnetic dynamo action realized by turbulent convection penetrating downward into a tachocline of rotational shear. This permits us to assess several dynamical elements believed to be crucial to the operation of the solar global dynamo, variously involving differential rotation resulting from convection, magnetic pumping, and amplification of fields by stretching within the tachocline. The simulations reveal that strong axisymmetric toroidal magnetic fields (about 3000 G in strength) are realized within the lower stable layer, unlike in the convection zone where fluctuating fields are predominant. The toroidal fields in the stable layer possess a striking persistent antisymmetric parity, with fields in the northern hemisphere largely of opposite polarity to those in the southern hemisphere. The associated mean poloidal magnetic fields there have a clear dipolar geometry, but we have not yet observed any distinctive reversals or latitudinal propagation. The presence of these deep magnetic fields appears to stabilize the sense of mean fields produced by vigorous dynamo action in the bulk of the convection zone.

Subfields: Astronomy and Astrophysics, Computational Mechanics, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/bf6f2890d9e01b598e2f12bb651279236e678323

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Citations in the corpus

MAGNETIC CYCLES IN GLOBAL LARGE-EDDY SIMULATIONS OF SOLAR CONVECTION (2010, background): “…showed that towards this end the presence of a stably stratified tachocline-like layer, where significant rotational shear could persist, allowed the buildup of a strong, large-scale magnetic component, antisymmetric about the equator and persistent on yearly timescales (Browning et al. 2006).”
CYCLIC MAGNETIC ACTIVITY DUE TO TURBULENT CONVECTION IN SPHERICAL WEDGE GEOMETRY (2012, background): “When such a layer is added, nonoscillatory large-scale fields are found also for solar parameters (Browning et al. 2006).”
MAGNETIC WREATHS AND CYCLES IN CONVECTIVE DYNAMOS (2012, background): “By adding an overshooting region of strong shear which mimics the solar tachocline, globalscale organization of the toroidal field was achieved by, but without reversals in global magnetic polarity over about 30 simulated years Browning et al. (2006).”
Structure and Evolution of Giant Cells in Global Models of Solar Convection (2007, background): “…parameter sensitivities, convective structure and transport, the maintenance of differential rotation and meridional circulation, and hydromagnetic dynamo processes (Miesch et al. 2000; Elliott et al. 2000; Brun & Toomre 2002; Brun et al. 2004; Miesch et al. 2006; Browning et al. 2006).”
Solar Dynamo Theory (2014, methodology): “The presence of a convectively stable, mechanically forced underlying fluid layer proved efficient at producing an axisymmetric large-scale component (Browning et al. 2006), which, however, remained resolutely steady over the time span of these simulations.”
Simulations of Dynamo Action in Fully Convective Stars (2007, methodology): “…by prior simulations of convection in the solar interior in comparable parameter regimes (Brun & Toomre 2002; Brun, Browning & Toomre 2005; Browning et al. 2006), for these have been relatively successful in matching the detailed observational constraints on, e.g., solar differential…”
Toroidal versus poloidal magnetic fields in Sun-like stars: a rotation threshold (2008, unknown): “Solar models with a tachocline lead to the building of strong large-scale toroidal fields confined to this interface layer (Browning et al. 2006, 2007), but the ability of these toroidal fields to travel the whole convective zone while keeping their identity remains nevertheless a matter of debate…”
PERSISTENT MAGNETIC WREATHS IN A RAPIDLY ROTATING SUN (2010, methodology): “In particular, Brun et al. (2004) explored Pm = 2,2.5 and 4, and Browning et al. (2006) studied Pm = 8.”
The Magnetic Connection between the Convection Zone and Corona in the Quiet Sun (2007, background): “…models of the solar magnetic field applicable to the deeper layers of the convective interior (e.g., Fan et al. 2003; Abbett et al. 2004; Browning et al. 2006) and models designed to describe the dynamic evolution of 1469 the outer corona (e.g., Roussev et al. 2004; Lionello et al.…”
MAGNETIC CYCLES IN A CONVECTIVE DYNAMO SIMULATION OF A YOUNG SOLAR-TYPE STAR (2011, background): “…overshoot region below the convection zone and a tachocline of rotational shear there promotes mean-field generation, producing persistent bands of toroidal flux antisymmetric about the equator while strengthening and stabilizing the dipole moment (Browning et al. 2006, 2007; Miesch et al. 2009).”