AAS 204th Meeting, June 2004
Session 47 When the Sun Went Wild
Topical Session, Tuesday, June 1, 2004, 2:30-4:00pm, 4:15-6:00pm, 702/704/706

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[47.01] Solar Flares as Probes of Particle Acceleration Processes

A.G. Emslie (UAH)

It has been established for some time now that solar flares accelerate copious quantities of charged particles, both electrons and ions. However, the number of particles accelerated and their associated current and energy fluxes, coupled with the relatively short time needed to accomplish the acceleration, continue to offer fundamental challenges to our understanding of the underlying physics. Such challenges include: How can the energy stored in sheared magnetic fields be dissipated on timescales that are orders of magnitude shorter than the classical resistive diffusion time? How can such a large fraction of the stored magnetic energy be converted into low-entropy acceleration rather than high-entropy heating? How can the huge electric currents involved be ``turned on'' in such a short time and without generating unacceptably large magnetic fields? How are the accelerated particles recycled many times through the acceleration process?

A variety of theoretical models for particle acceleration in solar flares, ranging from large-scale weak electric fields to small-scale strong electric fields to cascading hydromagnetic turbulence, have been proposed. Each of these models has its particular answers to the above questions and each has its particular predictions regarding the spectrum, directivity, and spatial distribution of the accelerated particles. Discrimination amongst models is, therefore, possible, but only through analysis of the associated radiation fields on time and size scales of physical interest. The Ramaty High Energy Solar Spectroscopic Imager (RHESSI) was designed to perform just this analysis of the X-ray and gamma-ray emissions, and it has indeed started to offer new insights into particle acceleration and transport processes in solar flares.

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