Magnetic and rotational quenching of the Λ effect
Context. Differential rotation in stars is driven by the turbulent transport of angular momentum. Aims. Our aim is to measure and parameterize the non-diffusive contribution to the total (Reynolds plus Maxwell) turbulent stress, known as the Λ effect, and its quenching as a function of rotation and...
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ftpubman:oai:pure.mpg.de:item_3166691 2023-08-27T04:11:06+02:00 Magnetic and rotational quenching of the Λ effect Käpylä, M. 2019 http://hdl.handle.net/21.11116/0000-0006-5BAF-0 eng eng info:eu-repo/semantics/altIdentifier/doi/10.1051/0004-6361/201732519 http://hdl.handle.net/21.11116/0000-0006-5BAF-0 Astronomy and Astrophysics info:eu-repo/semantics/article 2019 ftpubman https://doi.org/10.1051/0004-6361/201732519 2023-08-02T00:17:12Z Context. Differential rotation in stars is driven by the turbulent transport of angular momentum. Aims. Our aim is to measure and parameterize the non-diffusive contribution to the total (Reynolds plus Maxwell) turbulent stress, known as the Λ effect, and its quenching as a function of rotation and magnetic field. Methods. Simulations of homogeneous, anisotropically forced turbulence in fully periodic cubes are used to extract their associated turbulent Reynolds and Maxwell stresses. The forcing is set up such that the vertical velocity component dominates over the horizontal ones, as in turbulent stellar convection. This choice of the forcing defines the vertical direction. Additional preferred directions are introduced by the imposed rotation and magnetic field vectors. The angle between the rotation vector and the vertical direction is varied such that the latitude range from the north pole to the equator is covered. Magnetic fields are introduced by imposing a uniform large-scale field on the system. Turbulent transport coefficients pertaining to the Λ effect are obtained by fitting. The results are compared with analytic studies. Results. The numerical and analytic results agree qualitatively at slow rotation and low Reynolds numbers. This means that vertical (horizontal) transport is downward (equatorward). At rapid rotation the latitude dependence of the stress is more complex than predicted by theory. The existence of a significant meridional Λ effect is confirmed. Large-scale vorticity generation is found at rapid rotation when the Reynolds number exceeds a threshold value. The Λ effect is severely quenched by large-scale magnetic fields due to the tendency of the Reynolds and Maxwell stresses to cancel each other. Rotational (magnetic) quenching of Λ occurs at more rapid rotation (at lower field strength) in the simulations than in the analytic studies. Conclusions. The current results largely confirm the earlier theoretical results, and also offer new insights: the non-negligible meridional Λ effect ... Article in Journal/Newspaper North Pole Max Planck Society: MPG.PuRe North Pole Astronomy & Astrophysics 622 A195 |
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Open Polar |
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Max Planck Society: MPG.PuRe |
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language |
English |
description |
Context. Differential rotation in stars is driven by the turbulent transport of angular momentum. Aims. Our aim is to measure and parameterize the non-diffusive contribution to the total (Reynolds plus Maxwell) turbulent stress, known as the Λ effect, and its quenching as a function of rotation and magnetic field. Methods. Simulations of homogeneous, anisotropically forced turbulence in fully periodic cubes are used to extract their associated turbulent Reynolds and Maxwell stresses. The forcing is set up such that the vertical velocity component dominates over the horizontal ones, as in turbulent stellar convection. This choice of the forcing defines the vertical direction. Additional preferred directions are introduced by the imposed rotation and magnetic field vectors. The angle between the rotation vector and the vertical direction is varied such that the latitude range from the north pole to the equator is covered. Magnetic fields are introduced by imposing a uniform large-scale field on the system. Turbulent transport coefficients pertaining to the Λ effect are obtained by fitting. The results are compared with analytic studies. Results. The numerical and analytic results agree qualitatively at slow rotation and low Reynolds numbers. This means that vertical (horizontal) transport is downward (equatorward). At rapid rotation the latitude dependence of the stress is more complex than predicted by theory. The existence of a significant meridional Λ effect is confirmed. Large-scale vorticity generation is found at rapid rotation when the Reynolds number exceeds a threshold value. The Λ effect is severely quenched by large-scale magnetic fields due to the tendency of the Reynolds and Maxwell stresses to cancel each other. Rotational (magnetic) quenching of Λ occurs at more rapid rotation (at lower field strength) in the simulations than in the analytic studies. Conclusions. The current results largely confirm the earlier theoretical results, and also offer new insights: the non-negligible meridional Λ effect ... |
format |
Article in Journal/Newspaper |
author |
Käpylä, M. |
spellingShingle |
Käpylä, M. Magnetic and rotational quenching of the Λ effect |
author_facet |
Käpylä, M. |
author_sort |
Käpylä, M. |
title |
Magnetic and rotational quenching of the Λ effect |
title_short |
Magnetic and rotational quenching of the Λ effect |
title_full |
Magnetic and rotational quenching of the Λ effect |
title_fullStr |
Magnetic and rotational quenching of the Λ effect |
title_full_unstemmed |
Magnetic and rotational quenching of the Λ effect |
title_sort |
magnetic and rotational quenching of the λ effect |
publishDate |
2019 |
url |
http://hdl.handle.net/21.11116/0000-0006-5BAF-0 |
geographic |
North Pole |
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North Pole |
genre |
North Pole |
genre_facet |
North Pole |
op_source |
Astronomy and Astrophysics |
op_relation |
info:eu-repo/semantics/altIdentifier/doi/10.1051/0004-6361/201732519 http://hdl.handle.net/21.11116/0000-0006-5BAF-0 |
op_doi |
https://doi.org/10.1051/0004-6361/201732519 |
container_title |
Astronomy & Astrophysics |
container_volume |
622 |
container_start_page |
A195 |
_version_ |
1775353600057278464 |