Over the past few years, in great part due to the acquisition of data from spacecraft observatories such as the NASA Solar Maximum Mission (SMM) and the Japanese Hinotori, a global picture of the impulsive phase of solar flares has started to emerge, in which the radiation signatures in different spectral regions are all seen to reflect the same underlying physical processes. The spacecraft data show that the hard X-ray source evolves temporally and spatially in a manner which is consistent with the predicted response of the atmosphere to flare energy input by collisional degradation of energetic electron beams. Spectral line profiles in soft X-rays reveal plasma emission measures and velocities which are broadly consistent with the predictions of these electron beam energy transport calculations of the group funded here. These and other results are encouraging, because observations over a wide range of wavelengths can indeed be used to address two of the most fundamental questions of solar flare physics - the nature and cause of the primary energy release, and the physics of the energy transport processes. The interplay between theory and observation has progressed well beyond a simple comparison of qualitative pictures. We are now at a stage where theoretical predictions can be used to refine theoretical models and so increase our understanding of the basic physics at work. This grant will support a program of work to continue this profitable line of analysis. It will address diagnostics of flare energy transport processes, notably those resulting from the acceleration and degradation of suprathermal electrons, in hard X-rays, soft X-rays, and EUV. In addition, it will critically examine the physics of the energy release and transport in such a picture of the impulsive phase of flares, refining existing models to include effects which have hitherto received only scant attention, such as reverse currents, plasma collective processes and non-uniform magnetic field geometry.
