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Title: On the area expansion of magnetic flux tubes in solar active regions

We calculated the three-dimensional (3D) distribution of the area expansion factors in a potential magnetic field, extrapolated from the high-resolution Hinode/SOT magnetogram of the quiescent active region NOAA 11482. Retaining only closed loops within the computational box, we show that the distribution of area expansion factors show significant structure. Loop-like structures characterized by locally lower values of the expansion factor are embedded in a smooth background. These loop-like flux tubes have squashed cross-sections and expand with height. The distribution of the expansion factors show an overall increase with height, allowing an active region core characterized by low values of the expansion factor to be distinguished. The area expansion factors obtained from extrapolation of the Solar Optical Telescope magnetogram are compared to those obtained from an approximation of the observed magnetogram by a series of 134 submerged charges. This approximation retains the general flux distribution in the observed magnetogram, but removes the small-scale structure in both the approximated magnetogram and the 3D distribution of the area expansion factors. We argue that the structuring of the expansion factor can be a significant ingredient in producing the observed structuring of the solar corona. However, due to the potential approximation used, these results maymore » not be applicable to loops exhibiting twist or to active regions producing significant flares.« less
Authors:
 [1] ;  [2] ;  [3]
  1. DAMTP, CMS, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA (United Kingdom)
  2. Astronomical Institute of the Academy of Sciences of the Czech Republic, Fričova 298, 251 65 Ondřejov (Czech Republic)
  3. NASA Marshall Space Flight Center, VP 62, Huntsville, AL 35812 (United States)
Publication Date:
OSTI Identifier:
22370207
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 796; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; APPROXIMATIONS; COMPUTERIZED SIMULATION; CROSS SECTIONS; DISTRIBUTION; EXPANSION; EXTRAPOLATION; GAMMA RADIATION; MAGNETIC FIELDS; MAGNETIC FLUX; RESOLUTION; SOLAR CORONA; SUN; TELESCOPES; THREE-DIMENSIONAL CALCULATIONS; ULTRAVIOLET RADIATION; X RADIATION