Active Region Loops and Microoares Seen by Sumer

A high resolution spectrograph observation of an active region at the limb, which was performed by Solar Ultraviolet Measurements of Emitted Radiation (SUMER) on board the Solar and Heliospheric Observatory (SOHO) on 1996 May 6, provides an unprecedented opportunity of studying the structures and dynamics of active region loops and microoares at transition region temperatures. The SUMER observation covered the main phase of a B-class are and produced one set of raster scan data in the lines O VI 1032, 1038, C II 1037 and H I Ly. The intensity, velocity, and line width maps of the active region which were constructed from the raster scan data reveal more than ten well-resolved loops. The loops can be categorized into four groups depending on temperature and dynamical state. The observation connrms that hot (T > 10 5 K) and cool (T < 10 5) loops exist in the active region. There is also a clear distinction between static loops and dynamical loops. Static loops are closed, form an arcade and have small bulk motions and small turbulent motions. On the other hand, dynamical loops are morphologically open and vertical, and have large bulk motions and large turbulent motions, so they appear to be under eruption. Interestingly the dynamical loops display rotating motions around the loop axes with rotating velocities up to 50 km s ?1. Microoares seen by SUMER are characterized by very bright kernels in the intensity maps. They occurred near the area where the static loops and the erupting loops are commonly rooted. The spectral prooles of the lines at the bright kernels are very broad and consist of three Doppler components: highly { 2 { blue-shifted, stationary, and highly red-shifted components. It is found that there are two kinds of bright kernels: hotter kernels which are very bright in the O VI and cooler kernels which are very bright in the Ly. The hotter bright kernels display very bright stationary components with two high velocity (red-shifted and blue-shifted) components whereas cooler kernels display only two high velocity components. The velocities of the high velocity components are from 60 to 120 km s ?1. The sizes of the bright kernels identiied from the intensity maps range from 1500 to 5000 km, but the sizes of coherent velocity structures identiied from spectrograms are found to be as large as 10000 km. Our results may shed light on our understanding of …