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Heavy Ion Composition

Heavy ions like carbon, oxygen, and iron in the solar wind offer clues about where the wind originated. These ions show clear differences between slow and fast solar wind, with transitions in their abundance patterns near 400 kilometers per second. This supports the idea of two broad types of wind, but also reveals possible mass- or charge-dependent effects that shape the ion mix, especially in fast wind. Helium, again, stands out with a distinct pattern compared to heavier ions.

Figure showing heavy ion composition data from the SWICS instrument onboard the ACE spacecraft and how it evolves with solar activity.
Heavy ion abundances in slow solar wind evolve with solar activity and the strength of this correlation increases with element mass. This suggests that the impact of gravitational settling at the Sun on heavy ions changes with solar activity. In fast wind, the correlations are weak, but we can't tell if this is because the time period of our observations is too short or there is no correlation between fast wind abundances and solar activity. From Alterman et al. (2025), Astronomy and Astrophysics.