On The Doppler Velocity of Emission Line Profiles Formed in the "Coronal Contraflow" that is the Chromosphere-Corona Mass Cycle

TL;DR

This paper investigates the chromosphere-corona mass cycle using imaging and spectroscopic diagnostics, revealing temperature-dependent flows, propagating disturbances, and draining material that influence emission line profiles and flow interpretations.

Contribution

It introduces a detailed analysis of Doppler velocity patterns in emission lines, highlighting the role of cooling and draining flows in the coronal mass cycle, which advances understanding of coronal dynamics.

Findings

Hot lines show blue-shifts of 5-10 km/s indicating upward flows.

Cool lines exhibit red-shifts of similar magnitude indicating downward flows.

Propagating disturbances have apparent speeds of 50-150 km/s.

Abstract

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.