What is the spatial distribution of magnetic helicity injected in a solar active region?

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What is the spatial distribution of magnetic helicity injected in a solar active region?

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dc.contributor.author Pariat, E. en_GB
dc.contributor.author Nindos, A. en_GB
dc.contributor.author Démoulin, P. en_GB
dc.contributor.author Berger, M.A. en_GB
dc.date.accessioned 2008-02-22T15:35:56Z en_GB
dc.date.accessioned 2011-01-25T10:33:47Z en_US
dc.date.accessioned 2013-03-20T12:31:45Z
dc.date.issued 2006 en_GB
dc.description.abstract Context. Magnetic helicity is suspected to play a key role in solar phenomena such as flares and coronal mass ejections. Several investigations have recently computed the photospheric flux of magnetic helicity in active regions. The derived spatial maps of the helicity flux density, called GA, have an intrinsic mixed-sign patchy distribution. Aims. Pariat et al. (2005) recently showed that GA is only a proxy of the helicity flux density, which tends to create spurious polarities. They proposed a better proxy, Gθ. We investigate here the implications of this new approach on observed active regions. Methods. The magnetic data are from MDI/SoHO instrument and the photospheric velocities are computed by local correlation tracking. Maps and temporal evolution of GA and Gθ are compared using the same data set for 5 active regions. Results. Unlike the usual GA maps, most of our Gθ maps show almost unipolar spatial structures because the nondominant helicity flux densities are significantly suppressed. In a few cases, the Gθ maps still contain spurious bipolar signals. With further modelling we infer that the real helicity flux density is again unipolar. On time-scales larger than their transient temporal variations, the time evolution of the total helicity fluxes derived from GA and Gθ show small differences. However, unlike GA, with Gθ the time evolution of the total flux is determined primarily by the predominant-signed flux while the nondominant-signed flux is roughly stable and probably mostly due to noise. Conclusions. Our results strongly support the conclusion that the spatial distribution of helicity injected into active regions is much more coherent than previously thought: on the active region scale the sign of the injected helicity is predominantly uniform. These results have implications for the generation of the magnetic field (dynamo) and for the physics of both flares and coronal mass ejections. en_GB
dc.identifier.citation 452 (2), pp. 623-630 en_GB
dc.identifier.doi 10.1051/0004-6361:20054643 en_GB
dc.identifier.uri http://hdl.handle.net/10036/19045 en_GB
dc.language.iso en en_GB
dc.publisher EDP Sciences en_GB
dc.relation.url http://dx.doi.org/10.1051/0004-6361:20054643 en_GB
dc.subject Sun: magnetic fields en_GB
dc.subject Sun: photosphere en_GB
dc.subject Sun: corona en_GB
dc.title What is the spatial distribution of magnetic helicity injected in a solar active region? en_GB
dc.type Article en_GB
dc.date.available 2008-02-22T15:35:56Z en_GB
dc.date.available 2011-01-25T10:33:47Z en_US
dc.date.available 2013-03-20T12:31:45Z
dc.identifier.issn 0004-6361 en_GB
dc.identifier.issn 1432-0746 en_GB
dc.description Copyright © 2006 EDP Sciences. This article appeared in Astronomy & Astrophysics 452 (2006) and may be found at http://www.aanda.org/index.php?option=article&access=doi&doi=10.1051/0004-6361:20054643 en_GB
dc.identifier.journal Astronomy and Astrophysics en_GB


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