Robert Walsh

The High-Resolution Coronal Imager (Hi-C) was launched for a third time on 29th May 2018, resulting in 329 s of 17.2 nm data of target active region AR 12712 were captured with a cadence of approx. 4 s, and a plate scale of 0.129 arcsec^2/pixel. Using this data co-aligned with SDO/AIA 17.1nm observations, this presentation will outline results from investigating the widths of 49 coronal structures. Firstly, evidence of substructure within the loops that is not detected by AIA will be outlined. It is found that Hi-C 2.1 can resolve individual sub-loop strands as small as approx. 202 km, though the more typical strand widths seen are around 513 km. With the aid of multi-scale Gaussian normalization, strands from a region of low emission that can only be visualized against the contrast of the darker, underlying moss – this part of the corona is filled with ubiquitous, low emission, low density magnetic strands. Secondly, even at these superior spatial scales there may be evidence for further substructuring within the HiC strands themselves. Thus, the width profile intensity variations are reproduced by simultaneously fitting multiple Gaussian profiles using a nonlinear least-squares curve-fitting method. In total, 183 Gaussian profiles are examined and the full width at half maximum determined with most frequent structural widths about 450–575 km with 47% of the strand widths beneath SDO/AIA 17.1nm resolution. These appear to be the result of multiple strands along the integrated line of sight that can be resolved, rather than being the consequence of even finer sub-resolution elements. Finally, the change of strand width along strand length is examined – open fan magnetic strand structures display an observational width increase from the base while closed structures show little variation. The implications of these results on coronal loop modelling will be discussed.