Plasma diagnostics of active-region evolution and implications for coronal heating

R Milligan, Pat Gallagher, Michail Mathioudakis, Francis Keenan, Shaun Bloomfield

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

A detailed study is presented of the decaying solar-active region NOAA 10103 observed with the Coronal Diagnostic Spectrometer (CDS), the Michelson Doppler Imager (MDI) and the Extreme-ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). Electron-density maps formed using Si x (356.03 angstrom/347.41 angstrom) show that the density varies from similar to 10(10) cm(-3) in the active-region core to similar to 7 x 108 cm-3 at the region boundaries. Over the 5 d of observations, the average electron density fell by similar to 30 per cent. Temperature maps formed using Fe XVI (335.41 angstrom)/Fe XIV (334.18 angstrom) show electron temperatures of similar to 2.34 x 10(6) K in the active-region core and similar to 2.10 x 10(6) K at the region boundaries. Similarly to the electron density, there was a small decrease in the average electron temperature over the 5-d period. The radiative, conductive and mass-flow losses were calculated and used to determine the resultant heating rate (P-H). Radiative losses were found to dominate the active-region cooling process. As the region decayed, the heating rate decreased by almost a factor of 5 between the first and last day of observations. The heating rate was then compared to the total unsigned magnetic flux (Phi(tot) = integral dA vertical bar B-z vertical bar), yielding a power law of the form P-H similar to Phi(0.81 +/- 0.32)(tot) This result suggests that waves rather than nanoflares may be the dominant heating mechanism in this active region.
Original languageEnglish
Pages (from-to)259-267
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Volume363
Issue number1
DOIs
Publication statusPublished - 11 Oct 2005

Keywords

  • Sun: activity
  • Sun: corona
  • Sun: evolution
  • Sun: UV radiation
  • Astrophysics

ASJC Scopus subject areas

  • Space and Planetary Science

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