DISCOVERY OF FINELY STRUCTURED DYNAMIC SOLAR CORONA OBSERVED IN THE Hi-C TELESCOPE

Abstract

In the Summer of 2012, the High-resolution Coronal Imager (Hi-C) flew on board a NASA sounding rocket and collected the highest spatial resolution images ever obtained of the solar corona. One of the goals of the Hi-C flight was to characterize the substructure of the solar corona. We therefore examine how the intensity scales from AIA resolution to Hi-C resolution. For each low-resolution pixel, we calculate the standard deviation in the contributing high-resolution pixel intensities and compare that to the expected standard deviation calculated from the noise. If these numbers are approximately equal, the corona can be assumed to be smoothly varying, i.e., have no evidence of substructure in the Hi-C image to within Hi-C's ability to measure it given its throughput and readout noise. A standard deviation much larger than the noise value indicates the presence of substructure. We calculate these values for each low-resolution pixel for each frame of the Hi-C data. On average, 70% of the pixels in each Hi-C image show no evidence of substructure. The locations where substructure is prevalent is in the moss regions and in regions of sheared magnetic field. We also find that the level of substructure varies significantly over the roughly 160 s of the Hi-C data analyzed here. This result indicates that the finely structured corona is concentrated in regions of heating and is highly time dependent.

The Width Distribution of Loops and Strands in the Solar Corona—Are We Hitting Rock Bottom?

“…Most interestingly, Brooks et al (2013) show an occurrence distribution of 91 hand-picked loops observed with Hi-C with a minimum Gaussian width of σ w = 90 km (FWHM=212 km) and an average Gaussian width of σ w = 272 km (FWHM=640 km), which is fully consistent with our result of a peak width (FWHM) of w p ≈ 550 km based on three orders of magnitude larger statistics. Winebarger et al (2014) conducted a statistical analysis of the noise characteristics of a Hi-C image and concluded that 70% of the pixels in each Hi-C image do not show evidence for significant substructures, which confirms the scarcity of thinner loop strands than observed so far (see also Fig. 11b, where no structures except data noise is visible).…”

Miniature loops in the solar corona

“…In the context of coronal imaging, HiC has an unprecedented plate scale of 0.1 pixel −1 , which corresponds to 73 km pixel −1 on the Sun. The image resolution estimated by Winebarger et al (2014) is 0.3 to 0.4 . The 4k×4k full-frame images were recorded with an exposure time of 2 s at a cadence of 5.5 s. The unprecedented spatial and temporal resolution achieved by the Hi-C allows us to carry out the detailed analysis of the small-scale arcsec-size structures discussed in the introduction that were not resolved by previous instruments.…”

A GLOBAL VIEW OF VELOCITY FLUCTUATIONS IN THE CORONA BELOW 1.3 R⊙ WITH CoMP

“…Current instrumentation indicates that the chromosphere and corona is finely structured, with typical transverse scales of ∼ 400 km (De Pontieu et al 2007a, Morton et al 2012, Brooks et al 2013, Morton & McLaughlin 2013, 2014, Winebarger et al 2014. The fine-scale structure is seen to support MHD waves, and theoretical considerations demonstrate that these (likely) over dense magnetic flux tubes act as waveguides, funnelling the wave energy through the solar atmosphere.…”