Spectroscopic Studies of Solar Corona VII. Formation of a Coronal Loop by Evaporation

Details Spectroscopic Studies of Solar Corona VII. Formation of a Coronal Loop by Evaporation Spectroscopic Studies of Solar Corona VII. Formation of a Coronal Loop by Evaporation

Feb 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005soph..226..201s&link_type=abstract

Solar Physics, Volume 226, Issue 2, pp.201-221

Physics

5

Scientific paper

We obtained time-sequence spectroscopic observations in (Fe x) 6374 Å and (Fe xiv) 5303 Å lines successively with the 25-cm coronagraph, and narrow-band and Doppler images in 5303 Å line by the 2-D 10-cm Doppler coronagraph “NOGIS” at the Norikura Solar Observatory, of a coronal region for about 7 h on 9 19 20, 2001. The raster scans were obtained with a quasi-periodicity of about 14 min and “NOGIS” obtained the images with an interval of about 1 min. The coronal region observed showed the formation of a coronal loop by a high-speed surge in the 6374 Å line rising from one of the footpoints of the loop. Off the limb spectroscopic observations in the 6374 Å line showed large velocities along the line of sight and vertical to the solar limb at the time of formation of the loop. The 5303 Å line observations showed negligible line-of-sight velocities and low vertical velocities when compared to those in the 6374 Å line. A hump in the intensity plots in 5303 Å with height appears to move up with respect to the solar limb with an average velocity of 4km s-1. The FWHM of the 6374 Å showed a much smaller value of about 0.7 Å near the foot point as compared to a value of 1.2 Å at larger heights at the beginning of observations. Later as the loop developed, the FWHM of 6374 Å line showed a gradual decrease along the loop up to 70″ from the limb, reached a minimum value of about 0.5 Å and then increased with height during the formation of the loop; this trend lasted for about 2 h. About 3 h after the beginning of the formation of the loop, the FWHM of 6374 Å emission line showed normal values and normal rate of increase with height with some fluctuations. The FWHM of the 5303 Å line did not show such variations along the loop and showed normal decrease in FWHM with height found earlier (Singh et al., 2003a). These observations suggest that a relatively cooler plasma at a temperature of about 0.7 MK or less (corresponding to minimum value of FWHM of 0.5 Å) was ejected from the transition region with a large velocity of about 48km s-1, heated up in the corona by some process and formed a coronal loop with a height of about 200″ above the limb that had lifetime greater than 4 h. It appears that the plasma moved from one of the footpoints and the loop was formed by evaporation of chromospheric plasma. No large-scale brightening and Hα flare were observed in this region during the observational period of 7 h.

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