The Ly-α profile and the downflow

Spectrometers can measure the motion along the line-of-sight, if the light-emitting atom is not at rest. Line profiles of Lyman-α (top) and Lyman-β (bottom) have been sorted by their plasma flow into six velocity bins, negative values (lower curves) correspond to upflows, positive values (upper curves) to downflows.

It is most obvious that the asymmetries of both lines are reversed, and there is a clear correspondence between asymmetry and downflows: the higher the downflow, the brighter the emission and the more asymmetric the profile. This indicates the presence of a persistent downflow in the magnetically structured atmosphere that plays a dominating role in the line profile formation.