Solar wind ion scattering by Alfvén-cyclotron fluctuations: ion temperature anisotropies versus relative alpha particle densities

Abstract

Analysis of plasma data from the ACE spacecraft for 4 months of solar wind observations shows negative statistical correlations between the T⊥/T∥ of alpha particles and the relative alpha particle density, as well as between the T⊥/T∥ of the protons and the relative alpha particle density. Here, the subscripts refer to directions perpendicular and parallel to the background magnetic field. Hybrid computer simulations of the interaction between an applied spectrum of steady Alfvén-cyclotron fluctuations and a solar-wind-like plasma also show negative correlations between the alpha particle and proton temperature anisotropies and the relative alpha particle density. These results imply that these correlations are signatures of ion scattering by Alfven-cyclotron fluctuations, and that such scattering occurs sporadically in the solar wind near Earth.