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Title: MAGNETIC HELICITY AND ENERGY SPECTRA OF A SOLAR ACTIVE REGION

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 as relative helicity, is around 4% and strongest at intermediate wavenumbers of k ≈ 0.4 Mm{sup –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 {sup –11/3} power law at large wavenumbers, which implies a k {sup –5/3} spectrum for the modulus of the current helicity. A k {sup –5/3} spectrum is also obtained for the magnetic energy. The energy spectra evaluated separately from the horizontal and vertical fields agree formore » wavenumbers below 3 Mm{sup –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.« less
Authors:
 [1] ;  [2] ;  [3]
  1. Key Laboratory of Solar Activity, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)
  2. Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, SE-10691 Stockholm (Sweden)
  3. Department of Physics, Moscow University, 119992 Moscow (Russian Federation)
Publication Date:
OSTI Identifier:
22365925
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 784; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CORRELATIONS; CURRENT DENSITY; ENERGY SPECTRA; FOURIER TRANSFORMATION; HELICITY; ISOTROPY; MAGNETIC FIELDS; SOUTHERN HEMISPHERE; SPACE; SUN; SUNSPOTS; TURBULENCE; VECTORS