Abstract
We studied the EUV line spectra of three flare observed with the NRL slit spectrograph on Skylab. The electron densities in the flare transition-zone plasmas are determined from density-sensitive lines of Si iii and O iv. The electron densities in all three flares studied were greatest during the flare maximum with values of the order of 1012 cm−3. The density decreases by a factor of 2 to 3 in the decay phase of the flares. The intensities of EUV lines from the flare chromospheric and transition-zone plasmas all are greatly enhanced. In contrast to lines for Oi, Ci, Feii and other chromospheric ions, the lines of Oiv and Nv and other transition-zone lines are not only enhanced but also very much broadened.
Fitting of the N v 1242 Å line with a two-gaussian model shows that for two of the flares studied, there is a red-shifted component in addition to an unshifted component. The shifted component in the N v line profiles is interpreted as due to a dynamic and moving plasma with a bulk motion velocity of 12 km s−1 for one flare and more than 70 km s−1 for the other. The broadened line profiles indicate that there are large turbulent mass motions with random velocities ranging from 30 to 80 km s−1.
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Ball Corporation. Now with NASA/Marshall Space Flight Center.
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Cheng, CC. Densities and mass motions in transition-zone plasmas in solar flares observed from Skylab. Sol Phys 65, 283–298 (1980). https://doi.org/10.1007/BF00152795
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DOI: https://doi.org/10.1007/BF00152795