Loop Structures at East Limb observed by SUMER 06.May.96

Oxygen VI

SUMER's high spatial resolution capability makes it possible to study the structure of magnetic loops comprising an active region. The pictures are taken in H Lyman beta (15 000 K) and O VI 1037 (300 000 K) simultaneously, with an exposure time of 7 seconds per raster and a raster step of 0.757 arcsec (oversampling). The pictures show intensity and Doppler shift of an active region at the east limb. The spatial average of Doppler shift is taken to be zero for reference; the Lyman line profile is assumed to be Gaussian for simplicity, even though it is not optically thin.

The inclined bright loop of the Lyman beta images is barely visible in the higher temperature O VI line images, meaning that it is cool. Interestingly, the Lyman beta Doppler shift of this loop changes its sign across the loop and has maxima of about 50 km/s at both edges. This indicates that the loop has strong whirling motions around it and is now underging a dynamic process. Hot loops well visible in the O VI line are usually extended higher than cool loops seen in the Lyman beta line and have Doppler shifts of about 20 km/s. It seems quite probable that there exists some dynamical connection between cool loops and hot loops.
Jongchul Chae

IED, 29.Jan.97