Alpha-to-proton Temperature Ratio Distributions Using Parker Solar Probe Measurements

Abstract

The distributions of the temperature excess of alphas to protons (ε) were studied using Parker Solar Probe measurements for Encounters 2 through 14. The distributions were mapped based on heliographic distance, Coulomb number, plasma β, and Alfvén Mach number (M A ). The importance of collisional effects in the thermalization of solar wind is observed for a wide range of Coulomb numbers. The distributions correlate better with N β and NM A than just N. Furthermore, evidence was found for a narrow region immediately above the Alfvén surface (1 < M A < 2) where ε has values much higher than the mass ratio.