MAGNETIC HELICITY AND ENERGY SPECTRA OF A SOLAR ACTIVE REGIONстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 30 апреля 2014 г.
Аннотация:We compute for the first time the magnetic helicity and energy spectra of the solar active region NOAA 11158 during
2011 February 11–15 at 20◦ southern heliographic latitude using observational photospheric vector magnetograms.
We adopt the isotropic representation of the Fourier-transformed two-point correlation tensor of the magnetic field.
The sign of the magnetic helicity turns out to be predominantly positive at all wavenumbers. This sign is consistent
with what is theoretically expected for the southern hemisphere. The magnetic helicity normalized to its theoretical
maximum value, here referred to asrelative helicity, is around 4% and strongest at intermediate wavenumbers of
k ≈ 0.4 Mm−1
, corresponding to a scale of 2π/k ≈ 16 Mm. The same sign and a similar value are also found for
the relative current helicity evaluated in real space based on the vertical components of magnetic field and current
density. The modulus of the magnetic helicity spectrum shows a k−11/3 power law at large wavenumbers, which
implies a k−5/3 spectrum for the modulus of the current helicity. A k−5/3 spectrum is also obtained for the magnetic
energy. The energy spectra evaluated separately from the horizontal and vertical fields agree for wavenumbers
below 3 Mm−1, corresponding to scales above 2 Mm. This gives some justification to our assumption of isotropy
and places limits resulting from possible instrumental artifacts at small scales.