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Fig. 2


Zoomed images of the TRACE field-of-view contained within the white box in Fig. 1. The upper-left image displays a true intensity image, while the upper-right panel reveals the corresponding loop-edge binary map used in the tracking algorithm of Jess et al. (2008). Locations of the loop footpoints are highlighted with green boxes in the left panel, giving an approximate loop length, L = 72.9  ± 2.8 Mm. An 11 000 km segment, incorporating a brightly emitting section of the loop edge, which is used in the search for higher harmonics is contained within the green dashed lines plotted in the upper panels. The lower-left panel displays an emission measure map, derived from near-simultaneous 171 Å and 195 Å TRACE images, with the corresponding colour scale in units of cm-5. Black boxes and dashed lines represent characteristics identical to those described above for the upper-left panel. The loop arcade intensity ( + ), averaged between the green dashed lines in the upper-left panel, is plotted in the lower-right panel as a percentage above the quiescent background. A Gaussian fit to the coronal loop under investigation is displayed using a solid black line. Green shading represents loop intensities greater than the fitted half-maximum, while cross-hatched red shading indicates regions of the loop structure with intensities below the half-maximum. Arrows mark the full-width at half-maximum, chosen to represent an estimate of the loop depth, found here to be ≈ 8 pixels, or ≈ 3000 km.

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