On the Unresolved Fine Structures of the Solar Atmosphere. III. Elemental Abundances Consideration

Abstract

Results from high-quality solar upper atmosphere observations in the 104-106 K range contradict predictions made by models that assume that a single class of structures stretching throughout the entire temperature domain, from the cold chromosphere to the hot corona, is responsible for all the radiation we see. As a result, I proposed that new types of structures—the unresolved fine structures (UFSs)—are responsible for most of the detected emission in the 3 × 106 ≤ Te ≤ 8 × 106 K. In a recent paper Wikstol, Judge, & Hansteen challenged the presence of UFSs by claiming that the interpretation of the data in terms of UFSs is not unique and is likely to be incorrect in the presence of plasmas with unresolved dynamics. Further, they claim that most or all of the evidence that was brought in support of the UFSs is amenable to a different, equally reasonable interpretation in which the transition region emission is at all times formed in the time-varying thermal interface between the corona and chromosphere. In this paper I discuss some of the assertions made by Wikstol and collaborators. I also bring evidence from elemental abundance studies that would be difficult to support with the Wikstol model. In contrast, the existence of UFSs is not contradicted by any of the new observations.