Observations of energy conversion in the solar flare plasma

Abstract

Soft x-ray spectroscopic observations give evidence for magnetic energy conversion in the solar atmosphere during flares. Non-thermal broadenings and blue-shifted components, observed in hot emission lines during the impulsive phase of flares, can be interpreted as a manifestation of magnetic energy conversion and of energy transport from the primary energy release site to the chromosphere, respectively. Large non-thermal broadenings in soft x-ray lines emitted from the coronal plasma are observed in the period immediately preceding the onset of solar flares and during the flare impulsive phase, suggesting a relation to the initiation of the primary process of energy release and particle acceleration. Non-thermal broadenings can be interpreted as turbulent mass motions in the regions where magnetic reconnection occurs. Blue wings in soft x-ray lines appear at the onset of flares, as evidence for chromospheric evaporation, in coincidence with the onset of the impulsive phase of energy release. The dynamics of the evaporating plasma depends on the mechanism of chromospheric heating, and, in turn, on the form of energy which is predominant in the coronal loops as a result of the primary energy release. The observed evaporation velocities suggest that particle beams play a dominant role in transferring energy along the loop, at least in large flares.