Variations in solar wind fractionation as seen by ACE/SWICS over a solar cycle and the implications for Genesis Mission results

TL;DR

This study analyzes ACE/SWICS data over a solar cycle to understand solar wind fractionation variations, revealing that high-FIP element fractionation varies with the cycle and correlates with solar wind speed, impacting Genesis mission results.

Contribution

It provides a detailed comparison of solar wind fractionation across different solar cycle phases and regimes, highlighting the mass-dependent nature of fractionation and its implications for solar composition measurements.

Findings

High-FIP element fractionation varies significantly over the solar cycle.

Fractionation correlates strongly with solar wind speed and mass.

Results impact correction methods for Genesis solar wind samples.

Abstract

We use ACE/SWICS elemental composition data to compare the variations in solar wind fractionation as measured by SWICS during the last solar maximum (1999-2001), the solar minimum (2006-2009) and the period in which the Genesis spacecraft was collecting solar wind (late 2001 - early 2004). We differentiate our analysis in terms of solar wind regimes (i.e. originating from interstream or coronal hole flows, or coronal mass ejecta). Abundances are normalized to the low-FIP ion magnesium to uncover correlations that are not apparent when normalizing to high-FIP ions. We find that relative to magnesium, the other low-FIP elements are measurably fractionated, but the degree of fractionation does not vary significantly over the solar cycle. For the high-FIP ions, variation in fractionation over the solar cycle is significant: greatest for Ne/Mg and C/Mg, less so for O/Mg, and the least for He/Mg. When abundance ratios are examined as a function of solar wind speed, we find a strong correlation, with the remarkable observation that the degree of fractionation follows a mass-dependent trend. We discuss the implications for correcting the Genesis sample return results to photospheric abundances.