Solar wind minor ions: Departures from thermal conditions

University of Michigan, Ann Arbor, Michigan, USA

Solar wind distribution functions in the heliosphere have been studied using ACE and Wind data. Departures from thermal equilibrium conditions are observed in both, coronal hole associated fast, and in low-speed solar wind. These deviations are indicative of wave-particles interactions at very high wave number. They are therefore of interest in the context of isotropisation of particles of higher energy, i.e., pickup ions. We present observations of velocity distribution functions of solar wind minor ions and interpret their non-thermal properties in the framework of statistical acceleration in the solar wind. We also discuss the implications for their injection into shock acceleration in CIR associated shocks.