Spectroscopic Property of Solar Flares in Different Lines

Using the data from the Multi-channel Infrared Solar Spectrograph (MISS) at Purple Mountain Observatory (PMO), we studied the spectroscopic property of solar flares in the H-alpha, Ca II 8542 and He I 10830 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 H-alpha line displays red-shift only and no wide-wing in the initial phase of a flare. Large broadening of the H-alpha line are observed in few minutes after flare onset within small regions of 3 –5 arcsec in both disk and limb flares with/without non-thermal process. Far wings similar to those with damping broadening appear not only in the H-alpha line but in the He I 10830 line as well in flares with non-thermal process. We sometimes detect weak far wings in the Ca II 8542 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 H-alpha profile is not a sufficient condition to distinguish whether a non-thermal electron process exists in a flare. The Ca II 8542 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 10830 line are detected only in small regions with strong X-ray emissions and away from sunspot umbrae. Meanwhile, the He I 10830 line is sensitive to the structure of flare plasma. Therefore, this line is suitable for discriminating the X-ray emission in regions above flaring plasma and valuable in profile simulations.