Observations and modelling of the solar wind composition variations

Abstract

The physical mechanisms that regulate the abundance of heavy ions in the solar wind are not well understood. Variations in composition are measured in the charge state of heavy ions as well as the abundance of alpha particles and of elements with low first ionisation potential (FIP). The ionisation state and the abundance of heavy ions remain unchanged beyond the solar corona in the solar wind. Since the slow and fast solar winds have very different compositions, the slow wind being enriched in low-FIP elements, it has been argued that they must form through different processes in the solar corona. We analyse solar wind data taken in situ at different points in the inner heliosphere by Parker Solar Probe, Solar Orbiter and ACE to study the relation between ion abundances and solar wind properties (focusing on plasma moments, cross-helicity and non-thermal particles). This leads us to classify the different solar wind types according their composition and Alfvénicity during the different phases of the solar cycle. We then compare this classification with recent results of a new multi-species model of the solar corona and solar wind to study the various mechanisms potentially controlling solar wind composition, including diffusion processes and wave-particle interactions, to regulate heavy ion abundances. This work was funded by the ERC SLOW SOURCE project.