Spectroscopic studies of the solar corona , using the high spatial and spectral resolution 25-cm coronagraph at the Norikura observatory for equatorial off-limb observations , indicated that the variation of radiance and line width with height is different for different temperature lines .
The line width of the forbidden red emission line [ Fe x ] 6374 Å was found to increase with height and that of the green emission line [ Fe xiv ] 5303 Å decrease with height .
This had been interpreted in terms of the interaction between different temperature plasma but needed to be confirmed .
Further observations were made on several days during 2004 , in two emission lines simultaneously covering the mid-latitude and polar regions to investigate the existence of the observed variation in other parts of the solar corona .
In this study , we have analysed several raster scans that cover mid- and high-latitude regions of the off-limb corona in all four bright emission lines [ Fe x ] 6374 Å , [ Fe xi ] 7892 Å , [ Fe xiii ] 10747 Å , and [ Fe xiv ] 5303 Å .
We find that the FWHM of the red line increases with height and that of the green line decreases with height similar to that observed in equatorial regions .
The line widths are found to be higher in polar regions for all of the observed emission lines except for the green line .
Higher values of FWHM in polar regions may imply higher non-thermal velocities which could be further linked to a non-thermal source powering the solar-wind acceleration , but the reason for the behaviour of the green emission line remains to be explored .