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Paper: Spectroscopic Properties of Solar Flares in Different Lines
Volume: 368, The Physics of Chromospheric Plasmas
Page: 447
Authors: Li, H.; You, J.
Abstract: Using the data from the Multi-channel Infrared Solar Spectrograph (MISS) at Purple Mountain Observatory (PMO), we studied the spectroscopic properties of solar flares in the Hα, Ca II, and He I lines in different phases of flares, in diverse layers of flaring atmosphere, and in various locations of flares on the Sun. Our results show that the Hα line displays red-shift only and no wide-wing in the initial phase of a flare. Large broadening of the Hα line are observed in few minutes after flare onset within small regions of 3 – 5″ in both disk and limb flares with/without non-thermal process. Far wings similar to those with damping broadening appear not only in the Hα line but in the He I line as well in flares with non-thermal process. We sometimes detect weak far wings in the Ca II line in disk flares. Such large broadenings are observed in both the footpoints and the tops of flare loops, and possibly result from strong turbulence and/or macroscopic motion. Therefore, the so-called non-thermal wing of Hα profile is not a sufficient condition to distinguish whether a non-thermal electron process exists in a flare. The Ca II line shows lower intensity on the loop-tops and higher intensity in the parts of loops close to the solar surface. Emissions larger than continuum in the He I line are detected only in small regions with strong X-ray emissions and away from sunspot umbrae. Meanwhile, the He I line is sensitive to the structure of flare plasma. Therefore, this line is suitable for discriminating the X-ray emission in regions above flring plasma and valuable in profile simulations.
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