What is the source of the magnetic helicity shed by CMEs? The long-term helicity budget of AR 7978

An isolated active region (AR) was observed on the Sun during seven rotations, starting from its birth in July 1996 to its full dispersion in December 1996. We analyse the long-term budget of the AR relative magnetic helicity. Firstly, we calculate the helicity injected by differential rotation at t...

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Guardado en:
Detalles Bibliográficos
Publicado: 2002
Materias:
Solar-terrestrial relations
Sun: corona
Sun: coronal mass ejections (CMEs)
Sun: magnetic fields
Magnetic field effects
Magnetic flux
Solar radiation
Sun
X rays
Coronal mass ejections (CME)
Magnetic clouds
Magnetic helicity
Solar rotations
Astrophysics
Acceso en línea:https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00046361_v382_n2_p650_Demoulin
http://hdl.handle.net/20.500.12110/paper_00046361_v382_n2_p650_Demoulin
Aporte de:
Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
id paper:paper_00046361_v382_n2_p650_Demoulin
record_format dspace
spelling paper:paper_00046361_v382_n2_p650_Demoulin2023-06-08T14:27:26Z What is the source of the magnetic helicity shed by CMEs? The long-term helicity budget of AR 7978 Solar-terrestrial relations Sun: corona Sun: coronal mass ejections (CMEs) Sun: magnetic fields Magnetic field effects Magnetic flux Solar radiation Sun X rays Coronal mass ejections (CME) Magnetic clouds Magnetic helicity Solar rotations Astrophysics An isolated active region (AR) was observed on the Sun during seven rotations, starting from its birth in July 1996 to its full dispersion in December 1996. We analyse the long-term budget of the AR relative magnetic helicity. Firstly, we calculate the helicity injected by differential rotation at the photospheric level using MDI/SoHO magnetograms. Secondly, we compute the coronal magnetic field and its helicity selecting the model which best fits the soft X-ray loops observed with SXT/Yohkoh. Finally, we identify all the coronal mass ejections (CMEs) that originated from the AR during its lifetime using LASCO and EIT/SoHO. Assuming a one to one correspondence between CMEs and magnetic clouds, we estimate the magnetic helicity which could be shed via CMEs. We find that differential rotation can neither provide the required magnetic helicity to the coronal field (at least a factor 2.5 to 4 larger), nor to the field ejected to the interplanetary space (a factor 4 to 20 larger), even in the case of this AR for which the total helicity injected by differential rotation is close to the maximum possible value. However, the total helicity ejected is equivalent to that of a twisted flux tube having the same magnetic flux as the studied AR and n number of turns in the interval [0.5, 2.0]. We suggest that the main source of helicity is the inherent twist of the magnetic flux tube forming the active region. This magnetic helicity is transferred to the corona either by the continuous emergence of the flux tube for several solar rotations (i.e. on a time scale much longer than the classical emergence phase), or by torsional Alfvén waves. 2002 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00046361_v382_n2_p650_Demoulin http://hdl.handle.net/20.500.12110/paper_00046361_v382_n2_p650_Demoulin
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic Solar-terrestrial relations
Sun: corona
Sun: coronal mass ejections (CMEs)
Sun: magnetic fields
Magnetic field effects
Magnetic flux
Solar radiation
Sun
X rays
Coronal mass ejections (CME)
Magnetic clouds
Magnetic helicity
Solar rotations
Astrophysics
spellingShingle Solar-terrestrial relations
Sun: corona
Sun: coronal mass ejections (CMEs)
Sun: magnetic fields
Magnetic field effects
Magnetic flux
Solar radiation
Sun
X rays
Coronal mass ejections (CME)
Magnetic clouds
Magnetic helicity
Solar rotations
Astrophysics
What is the source of the magnetic helicity shed by CMEs? The long-term helicity budget of AR 7978
topic_facet Solar-terrestrial relations
Sun: corona
Sun: coronal mass ejections (CMEs)
Sun: magnetic fields
Magnetic field effects
Magnetic flux
Solar radiation
Sun
X rays
Coronal mass ejections (CME)
Magnetic clouds
Magnetic helicity
Solar rotations
Astrophysics
description An isolated active region (AR) was observed on the Sun during seven rotations, starting from its birth in July 1996 to its full dispersion in December 1996. We analyse the long-term budget of the AR relative magnetic helicity. Firstly, we calculate the helicity injected by differential rotation at the photospheric level using MDI/SoHO magnetograms. Secondly, we compute the coronal magnetic field and its helicity selecting the model which best fits the soft X-ray loops observed with SXT/Yohkoh. Finally, we identify all the coronal mass ejections (CMEs) that originated from the AR during its lifetime using LASCO and EIT/SoHO. Assuming a one to one correspondence between CMEs and magnetic clouds, we estimate the magnetic helicity which could be shed via CMEs. We find that differential rotation can neither provide the required magnetic helicity to the coronal field (at least a factor 2.5 to 4 larger), nor to the field ejected to the interplanetary space (a factor 4 to 20 larger), even in the case of this AR for which the total helicity injected by differential rotation is close to the maximum possible value. However, the total helicity ejected is equivalent to that of a twisted flux tube having the same magnetic flux as the studied AR and n number of turns in the interval [0.5, 2.0]. We suggest that the main source of helicity is the inherent twist of the magnetic flux tube forming the active region. This magnetic helicity is transferred to the corona either by the continuous emergence of the flux tube for several solar rotations (i.e. on a time scale much longer than the classical emergence phase), or by torsional Alfvén waves.
title What is the source of the magnetic helicity shed by CMEs? The long-term helicity budget of AR 7978
title_short What is the source of the magnetic helicity shed by CMEs? The long-term helicity budget of AR 7978
title_full What is the source of the magnetic helicity shed by CMEs? The long-term helicity budget of AR 7978
title_fullStr What is the source of the magnetic helicity shed by CMEs? The long-term helicity budget of AR 7978
title_full_unstemmed What is the source of the magnetic helicity shed by CMEs? The long-term helicity budget of AR 7978
title_sort what is the source of the magnetic helicity shed by cmes? the long-term helicity budget of ar 7978
publishDate 2002
url https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00046361_v382_n2_p650_Demoulin
http://hdl.handle.net/20.500.12110/paper_00046361_v382_n2_p650_Demoulin
_version_ 1768542107571585024

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