Twisted Flux Tube Emergence Evidenced in Longitudinal Magnetograms: Magnetic Tongues

Bipolar active regions (ARs) are thought to be formed by twisted flux tubes, as the presence of such twist is theoretically required for a cohesive rise through the whole convective zone. We use longitudinal magnetograms to demonstrate that a clear signature of a global magnetic twist is present, pa...

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Detalles Bibliográficos
Autores principales:	Luoni, Maria Luisa, Mandrini, Cristina Hemilse
Publicado:	2011
Materias:	Active regions, magnetic fields Corona, structures Helicity, magnetic Helicity, observations
Acceso en línea:	https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00380938_v270_n1_p45_Luoni http://hdl.handle.net/20.500.12110/paper_00380938_v270_n1_p45_Luoni
Aporte de:	Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires

id	paper:paper_00380938_v270_n1_p45_Luoni
record_format	dspace
spelling	paper:paper_00380938_v270_n1_p45_Luoni2023-06-08T15:02:45Z Twisted Flux Tube Emergence Evidenced in Longitudinal Magnetograms: Magnetic Tongues Luoni, Maria Luisa Mandrini, Cristina Hemilse Active regions, magnetic fields Corona, structures Helicity, magnetic Helicity, observations Bipolar active regions (ARs) are thought to be formed by twisted flux tubes, as the presence of such twist is theoretically required for a cohesive rise through the whole convective zone. We use longitudinal magnetograms to demonstrate that a clear signature of a global magnetic twist is present, particularly, during the emergence phase when the AR is forming in a much weaker pre-existing magnetic field environment. The twist is characterised by the presence of elongated polarities, called "magnetic tongues", which originate from the azimuthal magnetic field component. The tongues first extend in size before retracting when the maximum magnetic flux is reached. This implies an apparent rotation of the magnetic bipole. Using a simple half-torus model of an emerging twisted flux tube having a uniform twist profile, we derive how the direction of the polarity inversion line and the elongation of the tongues depend on the global twist in the flux rope. Using a sample of 40 ARs, we verify that the helicity sign, determined from the magnetic polarity distribution pattern, is consistent with the sign derived from the photospheric helicity flux computed from magnetogram time series, as well as from other proxies such as sheared coronal loops, sigmoids, flare ribbons and/or the associated magnetic cloud observed in situ at 1 AU. The evolution of the tongues observed in emerging ARs is also closely similar to the evolution found in recent MHD numerical simulations. We also found that the elongation of the tongue formed by the leading magnetic polarity is significantly larger than that of the following polarity. This newly discovered asymmetry is consistent with an asymmetric Ω-loop emergence, trailing the solar rotation, which was proposed earlier to explain other asymmetries in bipolar ARs. © 2011 Springer Science+Business Media B.V. Fil:Luoni, M.L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Mandrini, C.H. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. 2011 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00380938_v270_n1_p45_Luoni http://hdl.handle.net/20.500.12110/paper_00380938_v270_n1_p45_Luoni
institution	Universidad de Buenos Aires
institution_str	I-28
repository_str	R-134
collection	Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic	Active regions, magnetic fields Corona, structures Helicity, magnetic Helicity, observations
spellingShingle	Active regions, magnetic fields Corona, structures Helicity, magnetic Helicity, observations Luoni, Maria Luisa Mandrini, Cristina Hemilse Twisted Flux Tube Emergence Evidenced in Longitudinal Magnetograms: Magnetic Tongues
topic_facet	Active regions, magnetic fields Corona, structures Helicity, magnetic Helicity, observations
description	Bipolar active regions (ARs) are thought to be formed by twisted flux tubes, as the presence of such twist is theoretically required for a cohesive rise through the whole convective zone. We use longitudinal magnetograms to demonstrate that a clear signature of a global magnetic twist is present, particularly, during the emergence phase when the AR is forming in a much weaker pre-existing magnetic field environment. The twist is characterised by the presence of elongated polarities, called "magnetic tongues", which originate from the azimuthal magnetic field component. The tongues first extend in size before retracting when the maximum magnetic flux is reached. This implies an apparent rotation of the magnetic bipole. Using a simple half-torus model of an emerging twisted flux tube having a uniform twist profile, we derive how the direction of the polarity inversion line and the elongation of the tongues depend on the global twist in the flux rope. Using a sample of 40 ARs, we verify that the helicity sign, determined from the magnetic polarity distribution pattern, is consistent with the sign derived from the photospheric helicity flux computed from magnetogram time series, as well as from other proxies such as sheared coronal loops, sigmoids, flare ribbons and/or the associated magnetic cloud observed in situ at 1 AU. The evolution of the tongues observed in emerging ARs is also closely similar to the evolution found in recent MHD numerical simulations. We also found that the elongation of the tongue formed by the leading magnetic polarity is significantly larger than that of the following polarity. This newly discovered asymmetry is consistent with an asymmetric Ω-loop emergence, trailing the solar rotation, which was proposed earlier to explain other asymmetries in bipolar ARs. © 2011 Springer Science+Business Media B.V.
author	Luoni, Maria Luisa Mandrini, Cristina Hemilse
author_facet	Luoni, Maria Luisa Mandrini, Cristina Hemilse
author_sort	Luoni, Maria Luisa
title	Twisted Flux Tube Emergence Evidenced in Longitudinal Magnetograms: Magnetic Tongues
title_short	Twisted Flux Tube Emergence Evidenced in Longitudinal Magnetograms: Magnetic Tongues
title_full	Twisted Flux Tube Emergence Evidenced in Longitudinal Magnetograms: Magnetic Tongues
title_fullStr	Twisted Flux Tube Emergence Evidenced in Longitudinal Magnetograms: Magnetic Tongues
title_full_unstemmed	Twisted Flux Tube Emergence Evidenced in Longitudinal Magnetograms: Magnetic Tongues
title_sort	twisted flux tube emergence evidenced in longitudinal magnetograms: magnetic tongues
publishDate	2011
url	https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00380938_v270_n1_p45_Luoni http://hdl.handle.net/20.500.12110/paper_00380938_v270_n1_p45_Luoni
work_keys_str_mv	AT luonimarialuisa twistedfluxtubeemergenceevidencedinlongitudinalmagnetogramsmagnetictongues AT mandrinicristinahemilse twistedfluxtubeemergenceevidencedinlongitudinalmagnetogramsmagnetictongues
_version_	1768543551596003328

Twisted Flux Tube Emergence Evidenced in Longitudinal Magnetograms: Magnetic Tongues

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