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Abstract 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 () 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. 

Abstract Geocoronal Solar Wind Charge Exchange (SWCX) is the process by which heavy ions from the solar wind undergo charge exchange with neutral hydrogen atoms from the Earth's exosphere, releasing photons at discrete energies characteristic of the solar wind ions. This paper investigates the solar wind types driving geocoronal SWCX. We find that during periods of time‐variable SWCX, higher fractions of every ion species are recorded by ACE compared to the averages. Notably, a subset of the slow solar wind characterized by a systematic lower temperature and higher proton flux is surprisingly effective for producing SWCX. Given the degradation of the solar wind composition spectrometer on ACE in 2011, we explore the capabilities of XMM‐Newton as an alternative sensor to monitor heavy ion composition in the solar wind. Unlike the distributions of other ion line fluxes analyzed, only OVIII, extracted via spectral analysis of XMM‐Newton observations, display patterns similar to the corresponding parent ion abundances from ACE . Finally, we employ a Random Forest Classifier model to predict solar wind types based on literature results. When combining proton data with XMM‐Newton features, the model performance improves significantly, achieving a macro‐averaged F1 score of 0.80 (with a standard deviation of 0.06). 

Abstract The Earth's magnetosheath and cusps emit soft X‐rays due to the charge exchange between highly charged solar wind ions and exospheric hydrogen atoms. The Lunar Environment Heliospheric X‐ray Imager and Solar wind Magnetosphere Ionosphere Link Explorer missions are scheduled to image the Earth's dayside magnetosphere system in soft X‐rays to investigate global‐scale magnetopause reconnection modes under varying solar wind conditions. The exospheric neutral hydrogen density distribution, especially the value of this density at the subsolar magnetopause is of particular interest for understanding X‐ray emissions near this boundary. This paper estimates the exospheric density during solar minimum using the X‐ray Multimirror Mission (XMM) astrophysics observatory. We selected an event on 12 November 2008 from the XMM data archive, which detects soft X‐rays of magnetosheath origin while solar wind and interplanetary magnetic field conditions are relatively constant. During the event the location of the magnetopause was measured in situ by the THEMIS mission, thus the location of the solar wind ions responsible for the magnetosheath emission is well constrained by observation. We estimated the exospheric density using the Open Geospace Global Circulation Model (OpenGGCM) and a spherically symmetric exosphere model. The ratio of the magnetosheath plasma flux between the OpenGGCM model and the THEMIS, was nearly 1, which means the magnetohydrodynamic model reasonably reproduces the magnetosheath plasma conditions. The OpenGGCM magnetosheath parameters were used to deconvolve soft X‐rays of exospheric origin from the XMM signal. The lower‐limit of the exospheric density of this solar minimum event is 36.8 ± 11.7 cm⁻³at 10 R_Esubsolar location.