Properties of Suprathermal Ions in Solar Wind Compression Regions

Abstract:

Corotating interaction regions (CIRs) or more generally solar wind compression regions are believed to draw their source material from persistent but highly dynamic population of suprathermal (ST) particles with energies from a few keV up to 100’s of keV. Additionally, the suprathermal particle population is observed as an inverse power-law “tail” that smoothly connects to the thermal solar wind. Despite the prevalence of ST ions in interplanetary space, their origin is highly controversial primarily because many local and remote sources can contribute and cause large variations in tail properties such as intensity, density, spectral indices, and ion composition. Using solar wind, magnetic field, and suprathermal ion data (.02 -2 MeV/nuc) obtained by the Wind spacecraft, we perform a comprehensive study of the properties of ST ion populations associated with compression regions observed near Earth orbit from 1994 to 2014. This continuous, multi-year dataset has provided us with measurements over nearly two solar cycles (23 and 24) through differing solar wind and sunspot activity conditions. Our preliminary survey shows that the heavy ion spectral indices exhibit large variations on short (<1 year) and long (>1 year) timescales. We also investigate the relationships between the spectral indices, peak intensities, maximum energies, and various plasma properties such as compression ratios and solar wind speed changes, and use these statistical correlations to determine a set of new observational constraints for current acceleration models of suprathermal ions.