A Simple Model for Ion Acceleration and Transport at an Evolving Coronal/Interplanetary Shock
M. A. Lee
    University of New Hampshire, Durham NH, USA

The major processes responsible for the acceleration and transport of ions at a coronal/interplanetary shock are first reviewed. These include injection out of the solar wind or other low-energy particle populations such as interstellar pickup ions; diffusive shock acceleration at the evolving shock with varying solar wind density, shock compression ratio, and magnetic field obliquity; hydromagnetic wave excitation by the accelerated protons; escape of some fraction of the ions beyond the turbulent sheath upstream of the shock; and nearly scatter-free transport of those ions through interplanetary space to the observing spacecraft. A simple analytical model of these processes is then presented. The stationary ion spectrum accelerated at the shock, including wave excitation by the protons, is first calculated based on local shock parameters. These parameters are allowed to vary in the ion distributions and wave intensities as the shock evolves. The escape rate of the ions from the sheath is determined by balancing the focusing of the ions in the spherical magnetic field geometry with the rate of pitch-angle scattering. Finally, transport to an observer is determined by scatter-free transport. The model will be compared with characteristic solar energetic particle energy spectra and time profiles, as obtained, for example, by ACE and WIND.