Abstract
The discovery of active region moss, i.e., dynamic and bright upper transition region (TR) emission at chromospheric heights above active region plage, provides a powerful diagnostic to probe the structure, dynamics, energetics, and coupling of the magnetized solar chromosphere and TR. Here we present an observational study of the interaction of the chromosphere with the upper TR, by studying correlations (or lack thereof) between emission at varying temperatures: from the low chromosphere (Ca II K line), to the middle and upper chromosphere (H?), to the low TR (C IV ?1550 at 0.1 MK) and the upper TR (Fe IX/X ?171 at 1 MK and Fe XII ?195 at 1.5 MK). We use several data sets at high cadence (24-42 s) obtained with the Swedish Vacuum Solar Telescope (SVST, La Palma) and the Transition Region and Coronal Explorer (TRACE). This correlation analysis from low chromosphere to upper TR in active region plage quantifies and considerably expands on previous studies. Our results elucidate various issues, such as (1) how the heating mechanisms of the chromosphere and lower and upper TR are related (if at all), (2) how important heating of spicular jets is for the energy balance of the lower TR, (3) which timescales dominate the dynamic behavior of the active region TR, and (4) whether the spatial and temporal variability of moss can be used as a diagnostic for coronal heating.
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