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.

Keywords

• Solar energetic particles
• Solar wind
• Space weather