Evolution of Magnetic Helicity and Energy Spectra of Solar Active Regionsстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 20 апреля 2016 г.
Аннотация: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 30–60 Mm 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.
Key words: Sun: activity – dynamo – Sun: magnetic fields – Sun: photosphere