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S.V.H. Haugan, P. Brekke (ESA/GSFC), T. Fredvik, O. Kjeldseth-Moe (ITA, Oslo), K. Wilhelm (MPIAe, Germany), J. Gurman (NASA/GSFC)
A series of 218 rasters taken with the Coronal Diagnostic Spectrometer (CDS) on SOHO demonstrates the strong time variability and dynamical state of the plasma in active region loops at transition region temperatures, i.e. 10~000 K to 500~000 K, first reported by Kjeldseth-Moe and Brekke (1998). The continuous raster series, which covered 39 hours, show how transition region loops or sections of loops, 50-200 Mm in length, appear and disappear in intervals as short as 10 minutes, the observing cadence. At the same temperatures plasma velocities of 20 km s-1 to 100 km s-1 are indicated from observed Doppler shifts. Siphon flows may occur in some of the loops, but in other loops patterns are less obvious. High velocities are frequently seen where the emitted intensities are weak, often on the ``outside'' of the loops as defined by the emission in that particular spectral line. At coronal temperatures the emission is less time variable, but significant changes are seen. Systematic loop velocities occur only occasionally in the corona. Simultaneous observations with EIT and SUMER were made during part of the raster series and is compared with the CDS result.
The author(s) of this abstract have provided an email address for comments about the abstract: olavm@astro.uio.no