Plasma diagnostics of active-region evolution and implications for coronal heating
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 SiX (356.03 Å/347.41 Å) show that the density varies from ~1010cm-3 in the active-region core to ~7 × 108cm-3 at the region boundaries. Over the 5d of observations, the average electron density fell by ~30 per cent. Temperature maps formed using FeXVI (335.41 Å)/FeXIV (334.18 Å) show electron temperatures of ~2.34 × 106 K in the active-region core and ~2.10 × 106 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 (PH). 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 , yielding a power law of the form PH~Φ0.81+/-0.32tot. This result suggests that waves rather than nanoflares may be the dominant heating mechanism in this active region.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 2005
- DOI:
- 10.1111/j.1365-2966.2005.09446.x
- arXiv:
- arXiv:astro-ph/0509219
- Bibcode:
- 2005MNRAS.363..259M
- Keywords:
-
- Sun: activity;
- Sun: corona;
- Sun: evolution;
- Sun: UV radiation;
- Astrophysics
- E-Print:
- 9 pages, 11 figures. MNRAS, In Press