Ion collisional transport coefficients in the solar wind at 1 AU

TL;DR

This study quantifies ion collisional transport coefficients in the solar wind at 1 AU using WIND/SWE data, highlighting the importance of Coulomb collisions in slow solar wind streams for temperature anisotropies and particle deceleration.

Contribution

It provides detailed measurements of proton and alpha particle collisional coefficients at 1 AU, emphasizing their role in solar wind dynamics and the necessity of considering temperature anisotropies and differential streaming.

Findings

Coulomb collisions are significant in slow solar wind streams.

Collisions reduce temperature anisotropies and differential streaming.

Ion temperature anisotropies influence collisional transport coefficients.

Abstract

Proton and alpha particle collisional transport coefficients (isotropization, relative deceleration frequencies and heating rates) at 1 AU are quantified using the WIND/SWE data. In agreement with previous studies the ion-ion Coulomb collisions are generally important for slow solar wind streams and tend to reduce the temperature anisotropies, the differential streaming and the differences between proton and alpha particle temperatures. In slow solar wind streams the Coulomb collisions between protons and alpha particles are important for the overall proton energetics as well as for the relative deceleration between the two species. It is also shown that ion temperature anisotropies and differential streaming need to be generally taken into account for evaluation of the collisional transport coefficients.