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T. Fredvik, O. Kjeldseth-Moe (ITA), P. Brekke (ESA), S.V.H. Haugan (ITA)
The emission from plasma filled loops, 104 K < T <1.5 MK, above active regions are much more time variable than previously considered. These loops, which define the solar atmosphere above active regions in this temperature range, appear or disappear, the emission along their length change, or they change shape or expand outward, all on time scales of 10-20 minutes. In this paper we report on an investigation with CDS on SOHO of 20 loop systems observed on the solar limb between September 1997 and May 1998. We describe the apparent isothermal appearance of many loops and discuss to what extent loops radiating in different emission lines, i.e. at different temperatures, are co-located within their recorded widths. Finally, we demonstrate the time variability of loop systems at different temperatures, and show how the rapidly changing conditions require a new conception of loop systems that has never before been seriously considered.
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