EUV Analysis of a Quasi-static Coronal Loop Structure

Abstract

Decaying active region 10942 is investigated from 4:00 – 16:00 UT on 24 February 2007 using a suite of EUV observing instruments. Results from Hinode/EIS, STEREO and TRACE show that, although the active region has decayed and no sunspot is present, the physical mechanisms that produce distinguishable loop structures, spectral line broadening, and plasma flows still occur. A coronal loop that appears as a blue-shifted structure in Doppler maps is apparent in intensity images of log(T)=6.0 – 6.3 ions. The loop structure is found to be anti-correlated with spectral line broadening generally attributed to non-thermal velocities. This coronal loop structure is investigated physically (temperature, density, geometry) and temporally. Light curves created from imaging instruments show brightening and dimming of the loop structure on two different time scales; short pulses of 10 – 20 min and long duration dimming of two – four hours until its disappearance. The coronal loop structure, formed from relatively blue-shifted material that is anti-correlated with spectral line broadening, shows a density of 10¹⁰ to 10^9.3 cm⁻³ and is visible for longer than characteristic cooling times. The maximum non-thermal spectral line broadenings are found to be adjacent to the footpoint of the coronal loop structure.