Cool Plasma Observed in the FUV using IRIS

Abstract:

Cool plasma in the outer solar atmosphere is commonly observed in prominences and coronal rain. Theory suggests that these phenomena are related to cooling, and analysis of observations provides a constraint on the time-dependent energetics of the chromosphere and corona. Using the IRIS SG and SJI datasets, we discuss new observations of molecular absorption features in the Si IV emission lines near 1400A. The presence of molecules above the transition region provides an extreme example of complex structure and dynamics at the chromosphere-corona interface. There are two morphological models that can explain the absorption features: cool plasma hundreds of kilometers above the photosphere or a localized transition region deeply embedded in the photosphere. We discuss the merit of these scenarios and introduce complementary IRIS observations of inverted temperature structure in Ellerman bombs and diffuse Si I continuum absorption above active region loops.