- Physical Review Journals
All JournalsPhysics Magazine

Physical Review Research

Reuse & Permissions

It is not necessary to obtain permission to reuse this article or its components as it is available under the terms of the Creative Commons Attribution 4.0 International license. This license permits unrestricted use, distribution, and reproduction in any medium, provided attribution to the author(s) and the published article's title, journal citation, and DOI are maintained. Please note that some figures may have been included with permission from other third parties. It is your responsibility to obtain the proper permission from the rights holder directly for these figures.

Export citation

Export citation

Choose format for download:

Download Citation
  • Letter
  • Open Access

Strong large scale magnetic fields in rotating convection-driven dynamos: The important role of magnetic diffusion

Ming Yan and Michael A. Calkins*

  • Department of Physics, University of Colorado, Boulder, Colorado 80309, USA

  • *michael.calkins@colorado.edu
PDF

Phys. Rev. Research 4, L012026 – Published 23 February, 2022

DOI: https://doi.org/10.1103/PhysRevResearch.4.L012026

Abstract

Natural dynamos such as planets and stars generate a global scale magnetic field despite the inferred presence of small scale turbulence. Such systems are known as large scale dynamos and are typically driven by convection and influenced by rotation. Previous numerical studies of rotating dynamos generally find that the large scale magnetic field becomes weaker as the flow becomes more turbulent. The underlying physical processes necessary for sustaining so-called large scale dynamos is therefore still debated. Here, we use a suite of numerical simulations to show that strong large scale magnetic fields can be generated in rotating convective turbulence provided that two conditions are satisfied: (1) The flow remains rotationally constrained, and (2) magnetic diffusion is important on the small convective length scale. These findings are in agreement with previous asymptotic predictions and suggest that natural dynamos might satisfy these two conditions.

View figure in article

Physics Subject Headings (PhySH)

Article Text

References (31)

  1. C. A. Jones, Planetary magnetic fields and fluid dynamos, Annu. Rev. Fluid Mech. 43, 583 (2011).
  2. S. M. Tobias, The turbulent dynamo, J. Fluid Mech. 912, P1 (2021).
  3. E. N. Parker, Hydromagnetic dynamo models, Astrophys. J. 122, 293 (1955).
  4. M. Steenbeck, F. Krause, and K.-H. Rädler, A calculation of the mean electromotive force in an electrically conducting fluid in turbulent motion, under the influence of Coriolis forces, Z. Naturforsch. 21a, 369 (1966).
  5. H. K. Moffatt, An approach to a dynamic theory of dynamo action in a rotating conducting fluid, J. Fluid Mech. 53, 385 (1972).
  6. H. K. Moffatt, Dynamo action associated with random inertial waves in a rotating conducting fluid, J. Fluid Mech. 44, 705 (1970).
  7. U. Christensen and J. Aubert, Scaling properties of convection-driven dynamos in rotating shells and applications to planetary magnetic fields, Geophys. J. Int. 166, 97 (2006).
  8. F. Cattaneo and D. W. Hughes, Dynamo action in a rotating convective layer, J. Fluid Mech. 553, 401 (2006).
  9. A. Tilgner, Transitions in Rapidly Rotating Convection Driven Dynamos, Phys. Rev. Lett. 109, 248501 (2012).
  10. B. Favier and P. J. Bushby, On the problem of large-scale magnetic field generation in rotating compressible convection, J. Fluid Mech. 723, 529 (2013).
  11. M. A. Calkins, K. Julien, S. M. Tobias, and J. M. Aurnou, A multiscale dynamo model driven by quasi-geostrophic convection, J. Fluid Mech. 780, 143 (2015).
  12. M. A. Calkins, K. Julien, and S. M. Tobias, Inertia-less convectively-driven dynamo models in the limit of low Rossby number, Phys. Earth Planet. Inter. 266, 54 (2017).
  13. K. Julien, A. M. Rubio, I. Grooms, and E. Knobloch, Statistical and physical balances in low Rossby number Rayleigh-Bénard convection, Geophys. Astrophys. Fluid Dyn. 106, 392 (2012).
  14. C. Guervilly, P. Cardin, and N. Schaeffer, Turbulent convective length scale in planetary cores, Nature (London) 570, 368 (2019).
  15. J. M. Aurnou, S. Horn, and K. Julien, Connections between nonrotating, slowly rotating, and rapidly rotating turbulent convection transport scalings, Phys. Rev. Research 2, 043115 (2020).
  16. P. Marti, M. A. Calkins, and K. Julien, A computationally efficient spectral method for modeling core dynamics, Geochem. Geophys. Geosys. 17, 3031 (2016).
  17. M. Yan, M. A. Calkins, S. Maffei, K. Julien, S. M. Tobias, and P. Marti, Heat transfer and flow regimes in quasi-static magnetoconvection with a vertical magnetic field, J. Fluid Mech. 877, 1186 (2019).
  18. T. Vogt, S. Horn, and J. M. Aurnou, Oscillatory thermal–inertial flows in liquid metal rotating convection, J. Fluid Mech. 911, A5 (2021).
  19. M. A. Calkins, Quasi-geostrophic dynamo theory, Phys. Earth Planet. Inter. 276, 182 (2018).
  20. S. Schmitz and A. Tilgner, Transitions in turbulent rotating Rayleigh-Bénard convection, Geophys. Astrophys. Fluid Dyn. 104, 481 (2010).
  21. K. M. Soderlund, E. M. King, and J. M. Aurnou, The influence of magnetic fields in planetary dynamo models, Earth Planet. Sci. Lett. 333-334, 9 (2012).
  22. M. A. Calkins, L. Long, D. Nieves, K. Julien, and S. M. Tobias, Convection-driven kinematic dynamos at low Rossby and magnetic Prandtl numbers, Phys. Rev. Fluids. 1, 083701 (2016).
  23. J. Pietarila Graham, E. G. Blackman, P. D. Mininni, and A. Pouquet, Not much helicity is needed to drive large-scale dynamos, Phys. Rev. E 85, 066406 (2012).
  24. C. Guervilly, D. W. Hughes, and C. A. Jones, Generation of magnetic fields by large-scale vortices in rotating convection, Phys. Rev. E 91, 041001(R) (2015).
  25. C. Guervilly, D. W. Hughes, and C. A. Jones, Large-scale-vortex dynamos in planar rotating convection, J. Fluid Mech. 815, 333 (2017).
  26. P. J. Bushby, P. J. Käpylä, Y. Masada, A. Brandenburg, B. Favier, C. Guervilly, and M. J. Käpylä, Large-scale dynamos in rapidly rotating plane layer convection, Astron. Astrophys. 612, A97 (2018).
  27. P. J. Käpylä, M. J. Korpi, and A. Brandenburg, Large-scale dynamos in rigidly rotating turbulent convection, Astrophys. J. 697, 1153 (2009).
  28. N. Schaeffer, D. Jault, H.-C. Nataf, and A. Fournier, Turbulent geodynamo simulations: A leap towards Earth's core, Geophys. J. Int. 211, 1 (2017).
  29. B. Favier and M. R. E. Proctor, Kinematic dynamo action in square and hexagonal patterns, Phys. Rev. E 88, 053011 (2013).
  30. M. A. Calkins, K. Julien, and P. Marti, The breakdown of the anelastic approximation in rotating compressible convection: Implications for astrophysical systems, Proc. R. Soc. A 471, 20140689 (2015) .
  31. S. Li, S. Jaroszynski, S. Pearse, L. Orf, and J. Clyne, VAPOR: A visualization package tailored to analyze simulation data in earth system science, Atmosphere 10, 488 (2019).

Outline

Information

Phys. Rev. Research 4, L012026– Published 23 February, 2022
  • Received 23 September 2021
  • Accepted 9 February 2022
Crossmark - Check for updates button
Creative Commons Logo

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Sign In to Your Journals Account

Filter

Filter

Article Lookup

Enter a citation