EUV Analysis of a Quasi-Static Coronal Loop Structure

TL;DR

This study analyzes a decayed solar active region using EUV observations, revealing persistent loop structures, plasma flows, and spectral characteristics, providing insights into coronal loop dynamics even after active region decay.

Contribution

It provides a detailed physical and temporal analysis of a coronal loop in a decayed active region, highlighting the relationship between plasma flows, spectral broadening, and loop evolution.

Findings

Coronal loop shows blue-shifted plasma with densities of 10^10 to 10^9.3 cm^-3.

Loop brightening and dimming occur on 10-20 min and 2-4 hour timescales.

Maximum spectral line broadening is near the loop footpoint.

Abstract

Decaying active region 10942 is investigated from 4:00-16:00 UT on February 24, 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 nonthermal velocities. This coronal loop structure is investigated physically (temperature, density, geometry) and temporally. Lightcurves 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 2-4 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 10^10 to 10^9.3 cm-3 and is visible for longer than characteristic cooling times. The maximum nonthermal spectral line broadenings are found to be adjacent to the footpoint of the coronal loop structure.