2D histograms of Solar Orbiter HIS (left column) and ACE/SWICS (right column) measurements of C⁶⁺/C⁵⁺ versus O⁷⁺/O⁶⁺ ion ratios and O⁶⁺ thermal velocity against O⁶⁺ over Solar Orbiter’s first science orbit from January–June 2022 and ACE measurements collected between 1998–2011. The red solid and dashed lines in the plots of the top row show the linear fit of all 2007 SWICS data and an empirically selected offset below of the same slope, respectively, as done for Zhao et al. (2017b). The dashed line indicates periods in the solar wind where C⁶⁺/C⁵⁺ ratios fall outside of the typical correlated trend expected to O⁷⁺/O⁶⁺. The solar wind with C⁶⁺/C⁵⁺ values below the dashed line is the so-called “outlier wind”, whose value is lower than expected given an anonymously low C⁶⁺ abundance (see details in Sect. 5).