A Spectroscopic Study of the Solar Corona from Norikura and SOHO data

Abstract

We report the results from a spectroscopic study of the solar corona using both ground-based and space-based data. Some of the current topics in coronal physics, such as the plume-interplume differences in coronal holes and wave propagation in the corona have been examined. The distribution of emission line intensities, Doppler velocities and line widths were obtained from the spectroscopic observations from Norikura Solar Observatory of National Astronomical Observatory of Japan. The coronal images in Fe IX,X 171 Å and Fe XII 195 Å from SOHO EIT were used to get the temperature map of the corona. Combining both results, we have obtained the nonthermal velocities in the coronal hole region, without the usual assumption of a uniform ion temperature. It has been found that the histogram distributions of Doppler velocities and nonthermal velocities for coronal hole and quiet regions are markedly different. The nonthermal velocities have been found to be larger by about 27 %at the interplume regions as compared to plumes which supports the view that the interplume regions are the source regions of the fast solar wind. The analysis of the time sequence spectral data shows signatures of coronal oscillations at localized regions. Periods of the order of a few minutes have been found mainly in Doppler velocities.