Scott W. McIntosh, Hui Tian, Marybeth Sechler, Bart De Pontieu
This analysis begins to explore the complex chromosphere-corona mass cycle
using a blend of imaging and spectroscopic diagnostics. Single Gaussian fits to
hot emission line profiles (formed above 1MK) at the base of coronal loop
structures indicate material blue-shifts of 5-10km/s while cool emission line
profiles (formed below 1MK) yield red-shifts of a similar magnitude -
indicating, to zeroth order, that a temperature-dependent bifurcating flow
exists on coronal structures. Image sequences of the same region reveal weakly
emitting upward propagating disturbances in both hot and cool emission with
apparent speeds of 50-150km/s. Spectroscopic observations indicate that these
propagating disturbances produce a weak emission component in the blue wing at
commensurate speed, but that they contribute only a few percent to the
(ensemble) emission line profile in a single spatio-temporal resolution
element. Subsequent analysis of imaging data shows material "draining" slowly
(~10km/s) out of the corona, but only in the cooler passbands. We interpret the
draining as the return-flow of coronal material at the end of the complex
chromosphere-corona mass cycle. Further, we suggest that the efficient
radiative cooling of the draining material produces a significant contribution
to the red wing of cool emission lines that is ultimately responsible for their
systematic red-shift as derived from a single Gaussian fit when compared to
those formed in hotter (conductively dominated) domains. The presence of
counter-streaming flows complicates the line profiles, their interpretation,
and asymmetry diagnoses, but allows a different physical picture of the lower
corona to develop.
View original:
http://arxiv.org/abs/1202.1248
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