MAGNETIC WREATHS AND CYCLES IN CONVECTIVE DYNAMOS

By Nicholas J. Nelson, Benjamin P. Brown, A. Brun, Mark S. Miesch, J. Toomre. 2012

148 citations recorded by the source corpus.

Solar-type stars exhibit a rich variety of magnetic activity. Seeking to explore the convective origins of this activity, we have carried out a series of global three-dimensional magnetohydrodynamic simulations with the anelastic spherical harmonic code. Here we report on the dynamo mechanisms achieved as the effects of artificial diffusion are systematically decreased. The simulations are carried out at a nominal rotation rate of three times the solar value (3 Ω☉), but similar dynamics may also apply to the Sun. Our previous simulations demonstrated that convective dynamos can build persistent toroidal flux structures (magnetic wreaths) in the midst of a turbulent convection zone and that high rotation rates promote the cyclic reversal of these wreaths. Here we demonstrate that magnetic cycles can also be achieved by reducing the diffusion, thus increasing the Reynolds and magnetic Reynolds numbers. In these more turbulent models, diffusive processes no longer play a significant role in the key dynamical balances that establish and maintain the differential rotation and magnetic wreaths. Magnetic reversals are attributed to an imbalance in the poloidal magnetic induction by convective motions that is stabilized at higher diffusion levels. Additionally, the enhanced levels of turbulence lead to greater intermittency in the toroidal magnetic wreaths, promoting the generation of buoyant magnetic loops that rise from the deep interior to the upper regions of our simulated domain. The implications of such turbulence-induced magnetic buoyancy for solar and stellar flux emergence are also discussed.

Subfields: Astronomy and Astrophysics, Computational Mechanics, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/c66147d45949c4e4246625041e59ec3970655b12

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. Matthias Rempel
2. P. Williams
3. N. Wright
4. E. Newton
5. R. Yadav
6. J. Drake
7. Paul Charbonneau
8. Mark S. Miesch

In Computational Mechanics

1. Matthias Rempel
2. N. Wright
3. E. Newton
4. J. Drake
5. Paul Charbonneau

In Molecular Biology

1. Matthias Rempel
2. R. Yadav
3. Paul Charbonneau
4. Mark S. Miesch
5. J. Toomre
6. A. Brun
7. M. Browning

Citations in the corpus

• 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).”
• NUMERICAL SIMULATIONS OF QUIET SUN MAGNETISM: ON THE CONTRIBUTION FROM A SMALL-SCALE DYNAMO (2014, methodology): “Compared to that the energy extracted from large-scale mean flows in mean field dynamo models (Rempel 2006) as well as 3D global dynamo simulations (Nelson et al. 2013) is about 2 orders of magnitude smaller.”