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Paper: The Time Variable Solar Atmosphere - Dynamical and Variable Active Region Loops Observed with CDS on SOHO.
Volume: 184, Third Advances in Solar Physics Euroconference: Magnetic Fields and Oscillations
Page: 286
Authors: Kjeldseth-Moe, O.; Brekke, P.
Abstract: The Coronal Diagnostic Spectrometer, CDS, on SOHO has detected an upper solar atmosphere that is much more dynamic and time variable than previously expected. Loops in active regions, particularly in emission lines formed at temperatures 105 K to 1 MK, traditionally thought of as the transition region, are seen to change significantly over an hour. Loops appear or disappear, the emission along their length change, or they change shape or expand outward, all on time scales of 10-20 minutes. The structural variability is accompanied by high Doppler shifts, especially in the 2-5x105 K temperature range. Velocities corresponding to the shifts typically amount to +/- 50-100 km-1. We find that existing theoretical models for loops cannot explain the observations. However, models with extreme fine structure, combined with episodic heating and magneto-acoustic wave disturbances propagating in the loop legs seem promising. The rapidly changing conditions that we observe give a new conception of loop systems that has never before been seriously considered.
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