Active Region Loops Observed with SUMER on board

We study the structure and dynamics of active region magnetic loops at transition region temperatures by analyzing high resolution observations of the active region NOAA 7962 at the limb on 1996 May 6. During the decay phase of a B-class are which occurred at the active region, the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrograph on board the Solar and Heliospheric Observatory (SOHO) produced one set of raster scan data of the active region, in the four lines, The data were used to construct the intensity, velocity, and line width maps of the active region. From these maps, more than ten well-resolved loops are identiied and classiied into four diierent groups. We determine physical parameters of the loops such as diameter, length, density, temperature, line-of-sight velocity, and nonthermal broadening. It turns out that there is a distinction between stationary loops and dynamic loops. Dynamic loops have large bulk motions and large nonthermal broadenings. Some of dynamic loops appear to be erupting, and display rotational motions around the loop axes. The rotational velocities reach up to 50 km s ?1 , which may imply the existence of magnetic twist with B ' 1G. We also get some results which support that nonthermal broadenings are the result of magnetohydrodynamic turbulence in loops. Based on our observations, we postulate that when loops erupt, some of rotational and magnetic twist energy cascade down to turbulent energy which would be dissipated as heat. GOES X−ray Flux B C Fig. 1.| The spatial and temporal coverage of the SUMER observation as compared with a Yohkoh full disk image (box on left) and GOES low energy band X-ray data (shaded area on right).