Authors: Jia Huang (Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109, USA), Justin C. Kasper (Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109, USA; BWX Technologies, Inc., Washington DC 20001, USA), the SWEAP/FIELDS team
The Radial Evolution of Solar Wind Plasma in the Inner Heliosphere: PSP, Helios and Wind Observations
Jia Huang1, Justin C. Kasper1,2, the SWEAP/FIELDS team
1, Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109, USA. 2, BWX Technologies, Inc., Washington DC 20001, USA.
The evolution of solar wind is important to shed light on the heating and acceleration of solar wind. Previously, the radial evolution of solar wind was investigated mainly beyond 0.3 AU. As the Parker Solar Probe (PSP) has completed eleven encounters’ measurements in the inner heliosphere, with the closest perihelion being about 13.3 solar radii (Rs), it is timely to extend the study from beyond 0.3 AU to about 0.062 AU. Therefore, we combine the datasets from the PSP, Helios, and Wind to derive the radial trend of solar wind plasma in the inner heliosphere, and the differences between slow and fast solar winds are also compared. In this work, we have investigated the radial evolution indices for the density and temperature of electron, proton, and alpha particles, and we also check the evolution of alpha-proton differences, the pressure components, and the mass and momentum fluxes. As a result, we find 1) the PSP data have good quality; 2) stronger perpendicular heating and weaker parallel cooling of protons in the inner heliosphere; 3) the alpha shows more active characteristics when close to the Sun; 4) the mass and momentum fluxes imply the slow solar wind is still under expansion.