Empirical Functions for Highly Charged Ion Abundances in Solar Wind Charge Exchange Models: Addressing Post-2011 ACE Data Limitations

Upcoming imaging missions - NASA’s LEXI and ESA/CAS’s SMILE - will target solar wind charge exchange X-ray (SWCX) emission from Earth’s magnetosheath. This emission is generated by highly charged ions colliding with neutrals in Earth’s exosphere. Accurate SWCX models require data on exospheric neutral densities, as well as solar wind flux and composition. The Advanced Composition Explorer (ACE) Solar Wind Ionic Composition Spectrometer (SWICS) provided the needed solar wind composition data from 1998 until an instrument anomaly in 2011 limited its outputs. To address this, we developed empirical functions using ion ratios (O 7+ /O 6+ , O 8+ /O 6+ , C 6+ /C 5+ ) still available from ACE, partially compensating for missing composition data. The results underscore the need for a new mission to measure solar wind composition and support future SWCX analysis efforts.