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Nordita, Sweden; Stockholm University, Sweden; University of Colorado, United States;.ORCID iD: 0000-0002-7304-021X
2016 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 819, no 2, 146Article in journal (Refereed) PublishedText
Abstract [en]

We adopt an isotropic representation of the Fourier-transformed two-point correlation tensor of the magnetic field to estimate the magnetic energy and helicity spectra as well as current helicity spectra of two individual active regions (NOAA. 11158 and NOAA. 11515) and the change of the spectral indices during their development as well as during the solar cycle. The departure of the spectral indices of magnetic energy and current helicity from 5/ 3 are analyzed, and it is found that it is lower than the spectral index of the magnetic energy spectrum. Furthermore, the fractional magnetic helicity tends to increase when the scale of the energy-carrying magnetic structures increases. The magnetic helicity of NOAA. 11515 violates the expected hemispheric sign rule, which is interpreted as an effect of enhanced field strengths at scales larger than 30-60Mm with opposite signs of helicity. This is consistent with the general cycle dependence, which shows that around the solar maximum the magnetic energy and helicity spectra are steeper, emphasizing the large-scale field.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2016. Vol. 819, no 2, 146
Keyword [en]
Sun: activity, dynamo, Sun: magnetic fields, Sun: photosphere
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:kth:diva-185061DOI: 10.3847/0004-637X/819/2/146ISI: 000372305700058ScopusID: 2-s2.0-84960956287OAI: diva2:920056

QC 20160415

Available from: 2016-04-15 Created: 2016-04-11 Last updated: 2016-04-15Bibliographically approved

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Brandenburg, Axel
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