Different solar wind types reflected in pick-up ion spectral signatures

Abstract

In the more recent years several papers have been published which presented theoretical results concerning the phase-space behaviour of pick-up ions (PUIs) after their injection into the supersonic solar wind. PUI spectra thereby were obtained which revealed detailed spectral properties that could well be compared with observational data. Effects of convection, adiabatic deceleration, pitch-angle diffusion, and even of energy diffusion could clearly be identified. It was, however, becoming evident in the data that specific spectral differences between pick-up spectra in slow solar wind streams and in fast solar wind streams can be found. For instance, the high-energy shoulders of pick-up spectra beyond the injection energy were less pronounced in fast compared to slow solar wind streams. In order to come up with a more quantitative theoretical representation of this phenomenon we shall study in this paper the specifically different conditions for PUI phase-space transports in fast and in slow solar wind streams taking into account the type-specific main quantities governing pick-up ion phase-space motions like the injection velocities, the turbulence levels, and the exposure times.