16th AIAC: “Turbulence, Structures, and Particle Acceleration Throughout the Heliosphere and Beyond”

Preface The 16th Annual International Astrophysics Conference was held at the La Posada de Santa Fe hotel, Santa Fe, New Mexico, USA from March 6 to 10, 2017. The meeting entitled, "Turbulence, Structures, and Particle Acceleration Throughout the Heliosphere and Beyond", addressed the remarkable ability of nature to accelerate charged particles to extraordinarily high energies. This problem remains, after 100 years, one of the outstanding puzzles of solar and astrophysical plasmas. Diffusive shock acceleration (DSA) is thought to energize charged particles at shock waves. Steady-state DSA predictions include the particle intensity peaking at the shock, after which it is constant, and that the accelerated particle distribution is a power law with an index depending only on the shock compression ratio. DSA predictions are often but not always met. The anomalous cosmic ray spectrum was observed to peak behind the heliospheric termination shock and to possess a spectrum far harder than predicted by classical DSA theory. This is frequently true of shocks in the inner heliosphere and in astrophysical settings. Shocks are effective in generating magnetic turbulence and structures downstream and amplifying pre-existing turbulence, all factors in the further energization of charged particles. Furthermore, certain regions such as the heliospheric current sheet naturally produce complex turbulent environments in which numerous structures are present. Not surprisingly, in these regions observed energetic particle events, sometimes called anomalous solar energetic particle events, have characteristics quite unlike those predicted of typical impulsive or gradual solar energetic particle events. The purpose of this meeting was to explore the role of turbulence and structures (including magnetic reconnection-related processes, shock waves, etc.), in the acceleration of particles throughout the heliosphere and beyond. The meeting addressed current and past observations from spacecraft in the inner heliosphere, the distant heliosphere and very local interstellar medium, explored expectations and predictions for missions such as Solar Orbiter and Solar Probe Plus, now renamed as the Parker Solar Probe, and of course remote observations. Finally, we thank Adele Corona and ICNS for her continued excellent organization of the AIAC meetings and her help in providing the logistical support for this volume of papers.