Flare energy release: observational consequences and signatures

Abstract

It is generally accepted, but not yet compellingly demonstrated, that the energy released in solar flares is stored in stressed magnetic fields. Little is known, at present, about how the most obvious manifestations of flare energy release — heating, mass motion, magnetic field reconfiguration and particle acceleration — are related to the spatial distribution of free energy within those fields. To address this issue we have underway at Mees Solar Observatory a programme of simultaneous polarimetric and spectroscopic observations that allow us to explore the spatial relation between active region currents, flare particle acceleration and flare heating. In this paper we discuss several days observations of two flare-productive active regions. By using the Haleakala Stokes polarimeter, we observed the spatial distribution of the Stokes profiles of two photospheric Fe 1 lines, from which we inferred the spatial distribution of the vector m agnetic field and the vertical current density. In flares that were observed on the same days, we then compared the locations of vertical currents to the sites of non-thermal electron precipitation and high coronal pressure inferred from Hα line profiles and spectroheliograms obtained with the Mees charge coupled device imaging spectrograph. Without exception we found that the sites of significant energetic electron precipitation into the chromosphere were at the edges of regions of vertical current, not within them. In contrast, we found that the footpoints of high-pressure flare plasmas during the main phase of the observed flares all coincided very well with such currents.