Elementary Energy Release Events in Solar Flares

Most theoretical investigations of particle acceleration during solar flares cannot be applied to observations for detailed study of the time evolution. We propose a phenomenological model for turbulence evolution and stochastic particle acceleration that links observations to the energy release and particle acceleration through two coefficients characterising particle interactions with turbulent electromagnetic fields. In the linear regime the particle distribution does not affect the turbulence energy cascade. It is shown that electron acceleration critically depends on the intensity of small-scale turbulence and an impulsive nonthermal component only appears near the peak of the gradually evolving turbulence intensity. The model naturally reproduces the soft-hard-soft pattern of hard X-ray pulses, and we attribute the observed change in flux and spectral index correlation from the rise to decay phase of some pulses to changes in the background plasma. Detailed modelling of well-observed individual events will probe the energy release processes. Subject headings: Sun: flares — Sun: particle emission — acceleration of particles — plasmas — turbulence