Magnetic twist and writhe of active regions. On the origin of deformed flux tubes

We study the long term evolution of a set of 22 bipolar active regions (ARs) in which the main photospheric polarities are seen to rotate one around the other during several solar rotations. We first show that differential rotation is not at the origin of this large change in the tilt angle. A possi...

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Autores principales: López Fuentez, M.C., Démoulin, P., Mandrini, C.H., Pevtsov, A.A., Van Driel-Gesztelyi, L.
Formato: JOUR
Materias:
Magnetic fields
Methods: data analysis
Sun: interior
Sun: magnetic fields
Sun: photosphere
Extraterrestrial atmospheres
Mathematical models
Space research
Sun
Bipolar active regions
Magnetic twist
Photosphere
Astrophysics
Acceso en línea:http://hdl.handle.net/20.500.12110/paper_00046361_v397_n1_p305_LopezFuentez
Aporte de:
Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
id todo:paper_00046361_v397_n1_p305_LopezFuentez
record_format dspace
spelling todo:paper_00046361_v397_n1_p305_LopezFuentez2023-10-03T14:00:01Z Magnetic twist and writhe of active regions. On the origin of deformed flux tubes López Fuentez, M.C. Démoulin, P. Mandrini, C.H. Pevtsov, A.A. Van Driel-Gesztelyi, L. Magnetic fields Methods: data analysis Sun: interior Sun: magnetic fields Sun: photosphere Extraterrestrial atmospheres Magnetic fields Mathematical models Space research Sun Bipolar active regions Magnetic twist Photosphere Astrophysics We study the long term evolution of a set of 22 bipolar active regions (ARs) in which the main photospheric polarities are seen to rotate one around the other during several solar rotations. We first show that differential rotation is not at the origin of this large change in the tilt angle. A possible origin of this distortion is the nonlinear development of a kink-instability at the base of the convective zone; this would imply the formation of a non-planar flux tube which, while emerging across the photosphere, would show a rotation of its photospheric polarities as observed. A characteristic of the flux tubes deformed by this mechanism is that their magnetic twist and writhe should have the same sign. From the observed evolution of the tilt of the bipoles, we derive the sign of the writhe of the flux tube forming each AR; while we compute the sign of the twist from transverse field measurements. Comparing the handedness of the magnetic twist and writhe, we find that the presence of kink-unstable flux tubes is coherent with no more than 35% of the 20 cases for which the sign of the twist can be unambiguously determined. Since at most only a fraction of the tilt evolution can be explained by this process, we discuss the role that other mechanisms may play in the inferred deformation. We find that 36% of the 22 cases may result from the action of the Coriolis force as the flux tube travels through the convection zone. Furthermore, because several bipoles overpass in their rotation the mean toroidal (East-West) direction or rotate away from it, we propose that a possible explanation for the deformation of all these flux tubes may lie in the interaction with large-scale vortical motions of the plasma in the convection zone, including also photospheric or shallow sub-photospheric large scale flows. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_00046361_v397_n1_p305_LopezFuentez
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic Magnetic fields
Methods: data analysis
Sun: interior
Sun: magnetic fields
Sun: photosphere
Extraterrestrial atmospheres
Magnetic fields
Mathematical models
Space research
Sun
Bipolar active regions
Magnetic twist
Photosphere
Astrophysics
spellingShingle Magnetic fields
Methods: data analysis
Sun: interior
Sun: magnetic fields
Sun: photosphere
Extraterrestrial atmospheres
Magnetic fields
Mathematical models
Space research
Sun
Bipolar active regions
Magnetic twist
Photosphere
Astrophysics
López Fuentez, M.C.
Démoulin, P.
Mandrini, C.H.
Pevtsov, A.A.
Van Driel-Gesztelyi, L.
Magnetic twist and writhe of active regions. On the origin of deformed flux tubes
topic_facet Magnetic fields
Methods: data analysis
Sun: interior
Sun: magnetic fields
Sun: photosphere
Extraterrestrial atmospheres
Magnetic fields
Mathematical models
Space research
Sun
Bipolar active regions
Magnetic twist
Photosphere
Astrophysics
description We study the long term evolution of a set of 22 bipolar active regions (ARs) in which the main photospheric polarities are seen to rotate one around the other during several solar rotations. We first show that differential rotation is not at the origin of this large change in the tilt angle. A possible origin of this distortion is the nonlinear development of a kink-instability at the base of the convective zone; this would imply the formation of a non-planar flux tube which, while emerging across the photosphere, would show a rotation of its photospheric polarities as observed. A characteristic of the flux tubes deformed by this mechanism is that their magnetic twist and writhe should have the same sign. From the observed evolution of the tilt of the bipoles, we derive the sign of the writhe of the flux tube forming each AR; while we compute the sign of the twist from transverse field measurements. Comparing the handedness of the magnetic twist and writhe, we find that the presence of kink-unstable flux tubes is coherent with no more than 35% of the 20 cases for which the sign of the twist can be unambiguously determined. Since at most only a fraction of the tilt evolution can be explained by this process, we discuss the role that other mechanisms may play in the inferred deformation. We find that 36% of the 22 cases may result from the action of the Coriolis force as the flux tube travels through the convection zone. Furthermore, because several bipoles overpass in their rotation the mean toroidal (East-West) direction or rotate away from it, we propose that a possible explanation for the deformation of all these flux tubes may lie in the interaction with large-scale vortical motions of the plasma in the convection zone, including also photospheric or shallow sub-photospheric large scale flows.
format JOUR
author López Fuentez, M.C.
Démoulin, P.
Mandrini, C.H.
Pevtsov, A.A.
Van Driel-Gesztelyi, L.
author_facet López Fuentez, M.C.
Démoulin, P.
Mandrini, C.H.
Pevtsov, A.A.
Van Driel-Gesztelyi, L.
author_sort López Fuentez, M.C.
title Magnetic twist and writhe of active regions. On the origin of deformed flux tubes
title_short Magnetic twist and writhe of active regions. On the origin of deformed flux tubes
title_full Magnetic twist and writhe of active regions. On the origin of deformed flux tubes
title_fullStr Magnetic twist and writhe of active regions. On the origin of deformed flux tubes
title_full_unstemmed Magnetic twist and writhe of active regions. On the origin of deformed flux tubes
title_sort magnetic twist and writhe of active regions. on the origin of deformed flux tubes
url http://hdl.handle.net/20.500.12110/paper_00046361_v397_n1_p305_LopezFuentez
work_keys_str_mv AT lopezfuentezmc magnetictwistandwritheofactiveregionsontheoriginofdeformedfluxtubes
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AT mandrinich magnetictwistandwritheofactiveregionsontheoriginofdeformedfluxtubes
AT pevtsovaa magnetictwistandwritheofactiveregionsontheoriginofdeformedfluxtubes
AT vandrielgesztelyil magnetictwistandwritheofactiveregionsontheoriginofdeformedfluxtubes
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