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Hotta H, Bekki Y, Gizon L, Noraz Q, Rast M. Dynamics of Large-Scale Solar Flows. SPACE SCIENCE REVIEWS 2023; 219:77. [PMID: 38023293 PMCID: PMC10656343 DOI: 10.1007/s11214-023-01021-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/29/2023] [Accepted: 10/18/2023] [Indexed: 12/01/2023]
Abstract
The Sun's axisymmetric large-scale flows, differential rotation and meridional circulation, are thought to be maintained by the influence of rotation on the thermal-convective motions in the solar convection zone. These large-scale flows are crucial for maintaining the Sun's global magnetic field. Over the last several decades, our understanding of large-scale motions in the Sun has significantly improved, both through observational and theoretical efforts. Helioseismology has constrained the flow topology in the solar interior, and the growth of supercomputers has enabled simulations that can self-consistently generate large-scale flows in rotating spherical convective shells. In this article, we review our current understanding of solar convection and the large-scale flows present in the Sun, including those associated with the recently discovered inertial modes of oscillation. We discuss some issues still outstanding, and provide an outline of future efforts needed to address these.
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Affiliation(s)
- Hideyuki Hotta
- Institute for Space-Earth Environmental Research, Nagoya University, Chikusa-ku, Nagoya, Aichi 464-8601 Japan
| | - Yuto Bekki
- Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, Göttingen, 37077 Germany
| | - Laurent Gizon
- Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, Göttingen, 37077 Germany
- Institut für Astrophysik, Georg-August-Universtät Göttingen, Friedrich-Hund-Platz 1, Göttingen, 37077 Germany
| | - Quentin Noraz
- Rosseland Centre for Solar Physics, University of Oslo, P.O. Box 1029 Blindern, Oslo, NO-0315 Norway
- Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, Oslo, NO-0315 Norway
| | - Mark Rast
- Department of Astrophysical and Planetary Sciences, Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309 USA
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Varma V, Müller B. 3D simulations of oxygen shell burning with and without magnetic fields. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 2021; 504:636-647. [PMID: 33935581 PMCID: PMC8056252 DOI: 10.1093/mnras/stab883] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/01/2021] [Revised: 03/03/2021] [Accepted: 03/25/2021] [Indexed: 06/12/2023]
Abstract
We present a first 3D magnetohydrodynamic (MHD) simulation of convective oxygen and neon shell burning in a non-rotating [Formula: see text] star shortly before core collapse to study the generation of magnetic fields in supernova progenitors. We also run a purely hydrodynamic control simulation to gauge the impact of the magnetic fields on the convective flow and on convective boundary mixing. After about 17 convective turnover times, the magnetic field is approaching saturation levels in the oxygen shell with an average field strength of [Formula: see text], and does not reach kinetic equipartition. The field remains dominated by small-to-medium scales, and the dipole field strength at the base of the oxygen shell is only [Formula: see text]. The angle-averaged diagonal components of the Maxwell stress tensor mirror those of the Reynolds stress tensor, but are about one order of magnitude smaller. The shear flow at the oxygen-neon shell interface creates relatively strong fields parallel to the convective boundary, which noticeably inhibit the turbulent entrainment of neon into the oxygen shell. The reduced ingestion of neon lowers the nuclear energy generation rate in the oxygen shell and thereby slightly slows down the convective flow. Aside from this indirect effect, we find that magnetic fields do not appreciably alter the flow inside the oxygen shell. We discuss the implications of our results for the subsequent core-collapse supernova and stress the need for longer simulations, resolution studies, and an investigation of non-ideal effects for a better understanding of magnetic fields in supernova progenitors.
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Affiliation(s)
- Vishnu Varma
- School of Physics and Astronomy, 10 College Walk, Monash University, Clayton VIC 3800, Australia
| | - Bernhard Müller
- School of Physics and Astronomy, 10 College Walk, Monash University, Clayton VIC 3800, Australia
- ARC Centre of Excellence for Gravitational Wave Discovery – OzGrav, Monash University, Clayton, VIC 3800, Australia
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Hotta H, Iijima H, Kusano K. Weak influence of near-surface layer on solar deep convection zone revealed by comprehensive simulation from base to surface. SCIENCE ADVANCES 2019; 5:eaau2307. [PMID: 30613769 PMCID: PMC6314832 DOI: 10.1126/sciadv.aau2307] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2018] [Accepted: 11/28/2018] [Indexed: 06/04/2023]
Abstract
The solar convection zone is filled with turbulent convection in highly stratified plasma. Several theoretical and observational studies suggest that the numerical calculations overestimate the convection velocity. Since all deep convection zone calculations exclude the solar surface due to substantial temporal and spatial scale separations, the solar surface, which drives the thermal convection with efficient radiative cooling, has been thought to be the key to solve this discrepancy. Thanks to the recent development in massive supercomputers, we are successful in performing the comprehensive calculation covering the whole solar convection zone. We compare the results with and without the solar surface in the local domain and without the surface in the full sphere. The calculations do not include the rotation and the magnetic field. The surface region has an unexpectedly weak influence on the deep convection zone. We find that just including the solar surface cannot solve the problem.
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Affiliation(s)
- H. Hotta
- Department of Physics, Graduate School of Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan
| | - H. Iijima
- Division for Integrated Studies, Institute for Space-Earth Environmental Research, Nagoya University, Furocho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan
| | - K. Kusano
- Division for Integrated Studies, Institute for Space-Earth Environmental Research, Nagoya University, Furocho, Chikusa-ku, Nagoya, Aichi 464-8601, Japan
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Hotta H, Rempel M, Yokoyama T. Large-scale magnetic fields at high Reynolds numbers in magnetohydrodynamic simulations. Science 2016; 351:1427-30. [PMID: 27013727 DOI: 10.1126/science.aad1893] [Citation(s) in RCA: 77] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Accepted: 02/10/2016] [Indexed: 11/02/2022]
Abstract
The 11-year solar magnetic cycle shows a high degree of coherence in spite of the turbulent nature of the solar convection zone. It has been found in recent high-resolution magnetohydrodynamics simulations that the maintenance of a large-scale coherent magnetic field is difficult with small viscosity and magnetic diffusivity (≲10 (12) square centimenters per second). We reproduced previous findings that indicate a reduction of the energy in the large-scale magnetic field for lower diffusivities and demonstrate the recovery of the global-scale magnetic field using unprecedentedly high resolution. We found an efficient small-scale dynamo that suppresses small-scale flows, which mimics the properties of large diffusivity. As a result, the global-scale magnetic field is maintained even in the regime of small diffusivities-that is, large Reynolds numbers.
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Affiliation(s)
- H Hotta
- Department of Physics, Graduate School of Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan. High Altitude Observatory, National Center for Atmospheric Research (NCAR), Post Office Box 3000, Boulder, CO 80307, USA.
| | - M Rempel
- High Altitude Observatory, National Center for Atmospheric Research (NCAR), Post Office Box 3000, Boulder, CO 80307, USA
| | - T Yokoyama
- Department of Earth and Planetary Science, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
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Squire J, Bhattacharjee A. Generation of Large-Scale Magnetic Fields by Small-Scale Dynamo in Shear Flows. PHYSICAL REVIEW LETTERS 2015; 115:175003. [PMID: 26551120 DOI: 10.1103/physrevlett.115.175003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2015] [Indexed: 06/05/2023]
Abstract
We propose a new mechanism for a turbulent mean-field dynamo in which the magnetic fluctuations resulting from a small-scale dynamo drive the generation of large-scale magnetic fields. This is in stark contrast to the common idea that small-scale magnetic fields should be harmful to large-scale dynamo action. These dynamos occur in the presence of a large-scale velocity shear and do not require net helicity, resulting from off-diagonal components of the turbulent resistivity tensor as the magnetic analogue of the "shear-current" effect. Given the inevitable existence of nonhelical small-scale magnetic fields in turbulent plasmas, as well as the generic nature of velocity shear, the suggested mechanism may help explain the generation of large-scale magnetic fields across a wide range of astrophysical objects.
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Affiliation(s)
- J Squire
- Max Planck and Princeton Center for Plasma Physics, Department of Astrophysical Sciences and Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543, USA
- TAPIR, Mailcode 350-17, California Institute of Technology, Pasadena, California 91125, USA
| | - A Bhattacharjee
- Max Planck and Princeton Center for Plasma Physics, Department of Astrophysical Sciences and Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543, USA
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