Variation of Emission Line Width in Mid- and High-Latitude Corona

Abstract

Spectroscopic studies of the solar corona, using the high spatial and spectral resolution 25-cm coronagraph at the Norikura observatory for equatorial off-limb observations, indicated that the variation of radiance and line width with height is different for different temperature lines. The line width of the forbidden red emission line [\FeX] 6374 Åwas found to increase with height and that of the green emission line [\FeXIV] 5303 Ådecrease with height. This had been interpreted in terms of the interaction between different temperature plasma but needed to be confirmed. Further observations were made on several days during 2004, in two emission lines simultaneously covering the mid-latitude and polar regions to investigate the existence of the observed variation in other parts of the solar corona. In this study, we have analysed several raster scans that cover mid- and high-latitude regions of the off-limb corona in all four bright emission lines [\FeX] 6374 Å, [\FeXI] 7892 Å, [\FeXIII] 10747 Å, and [\FeXIV] 5303 Å. We find that the FWHM of the red line increases with height and that of the green line decreases with height similar to that observed in equatorial regions. The line widths are found to be higher in polar regions for all of the observed emission lines except for the green line. Higher values of FWHM in polar regions may imply higher non-thermal velocities which could be further linked to a non-thermal source powering the solar-wind acceleration, but the reason for the behaviour of the green emission line remains to be explored.

arXiv commentaccepted for publication in Solar physics

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Cited by in corpus (5)

• Solar UV and X-Ray Spectral Diagnostics
• MHD Waves in open coronal structures
• Thermal structure of coronal loops as seen with Norikura coronagraph
• Characteristics of the Solar Coronal Line Profiles from Fabry-Perot Interferometric Observations
• Investigating the Behavior and Spatiotemporal Variations of Green Line Emission in the Solar Corona