E.L. Chupp and P.P. Dunphy

University of New Hampshire, Durham, NH 03824

E. Aprile, A.Curioni, and U. Oberlack

Columbia University, New York,NY 10027

A major challenge in high energy solar physics is to identify the mechanism(s) that accelerate ions and electrons to energies as high as 1 GeV with initiation time scales as short as seconds, producing emissions that can extend from minutes to several hours. Therefore, we describe the characteristics of the accelerated particles which produce gamma-ray lines and continua, meson-decay gamma-rays, and high- energy neutrons as deduced from observations of several intense solar flares during solar sunspot cycles 21 and 22. Typically, the events consist of an impulsive gamma-ray burst or bursts lasting minutes, followed by an extended emission lasting up to hours. The extended emission often results from ions lasting up to hours. The extended emission often results from ions accelerated to at least several hundred MeV. We discuss briefly scenarios which have been considered to explain these high-energy flare phenomena: acceleration of ions by 2nd order Fermi acceleration in a closed magnetic loop, acceleration of particles by transient reconnection in magnetic fields at the top of the loop, acceleration of ions at a coronal mass ejection (CME) shock front, and acceleration in a corona stressed by a passing CME. In particular, we finally focus on suborbital experiments that can extend flare observations to high energies ( > 20 MeV) during the forthcoming maximum of cycle 23. Such observations will provide crucial information on the acceleration of the highest energy flare particles and could be simultaneous with the lower energy HESSI observations.