Other
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsh53a1059d&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SH53A-1059
Other
7509 Corona, 7549 Ultraviolet Emissions
Scientific paper
Optically thin ultraviolet, extreme-ultraviolet (EUV), and X-ray spectral lines emitted by ions in the solar transition region and corona usually have Gaussian widths in excess of the ion temperature thermal Doppler width expected assuming the ions are formed in ionization equilibrium. Also, because of the densities in the lower solar corona and transition region, the electron temperature is assumed to be equal to the ion temperature. The excess line widths do not produce asymmetries in the line profiles and are interpreted as a non-thermal random Doppler motion in the plasma producing the lines. First discovered in 1975, these mysterious motions are still unexplained. They may be a signature of wave propagation, magnetic reconnection, random unresolved bulk flows, or some other as yet unspecified physical mechanism. Up to the present, it has not been possible to relate these motions spatially to coronal structures in active regions in considerable detail. However, the recent launch of the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode spacecraft has made it now possible to establish detailed relationships. We analyze EUV coronal (i.e., lines from ions such as Fe XII) spectral lines obtained from EIS spectra of two active regions and discuss the relationship of the non-thermal line widths to the temperatures, densities, and positions in the active region loops and inter-loop regions. We also discuss the relationship of the line widths to line-of-sight flows in the active regions as determined from the centroid wavelengths of the spectral lines.
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