Plasma Diagnostics of Active Region Evolution and Implications for Coronal Heating

Details Plasma Diagnostics of Active Region Evolution and Implications for Coronal Heating Plasma Diagnostics of Active Region Evolution and Implications for Coronal Heating

May 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004aas...204.9803m&link_type=abstract

American Astronomical Society Meeting 204, #98.03; Bulletin of the American Astronomical Society, Vol. 36, p.984

Physics

Scientific paper

The decaying solar active region NOAA 10103 was observed during 2002 September 10--14 using the Coronal Diagnostic Spectrometer (CDS) onboard the Solar and Heliospheric Observatory (SOHO). Electron density maps were created using the Si X (356Å/347Å) ratio, which show densities of ˜1010cm-3 in the active region core, and ˜7x108cm-3 in the region boundaries. Over the five days of observations, the average electron density fell by approximately a factor of two. Temperature maps were created using the Fe XVI (335.4Å)/Fe XIV (334.2Å) ratio, which show electron temperatures of ˜2.2x106K in the active region core, and ˜2.0x106K in the region boundaries. Similarly to the electron density, the average electron temperature decreased over the five days, but by only ˜3%. The radiative and conductive losses, and resultant heating rate, were then calculated and compared to the total unsigned magnetic flux (Φ tot = ∫ dA |Bz|) from Michelson Doppler Interferometer (MDI) magnetograms. Losses due to radiation were found to exceed conductive losses by a factor of ten. As the region decayed, the heating rate decreased by close to an order of magnitiude between the first and last day of observations. In line with several coronal heating theories, a power-law relationship of the form Ptot} ˜Φ {tot0.95±0.07 was found between the heating rate and the unsigned magnetic flux. This result provides further observational evidence for wave rather than nanoflare heating of solar active regions.
Ryan Milligan would like to thank the Solar Physics Division for being awarded an SPD Studentship.

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