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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). 

The approximately 11-year solar cycle has been shown to impact the heavy ion composition of the solar wind, even when accounting for streams of differing speeds; however, the heavy ion composition observed between the same specific phases of a past solar cycle and the current cycle has rarely, if ever, been compared. Here, we compare the heavy ion composition of the solar wind, as measuredin situduring the solar cycle 23 and 25 ascending phases. We examine the mean iron and oxygen charge state composition and the O⁷⁺/O⁶⁺ratio in multiple ranges of associated bulk wind speeds. Then, we compare the iron and oxygen charge state composition and relative abundance of iron to oxygen in the traditionally defined fast and slow solar wind. Finally, to determine the impact of individual ion contributions on the solar wind iron abundance, we examine individual ratios of iron and oxygen ions. Although the charge state composition remained broadly similar between these two ascending phases, both the O⁷⁺/O⁶⁺ratio and iron fractionation in fast-speed streams were higher in the solar cycle 25 ascending phase than they were during the solar cycle 23 ascending phase, suggesting that equatorial coronal hole fields more frequently reconnected with helmet streamers or active regions in the latter of the two ascending phases; however, more work will need to be done to connect these observations back to their coronal origins. The individual ion ratios used in this work provided a spectrum to analyze the aggregate elemental abundances, and this work, as a whole, is an important step in determining how conditions in the corona may vary between solar cycles between the same phases. 

Abstract Connecting the solar wind observed throughout the heliosphere to its origins in the solar corona is one of the central aims of heliophysics. The variability in the magnetic field, bulk plasma, and heavy ion composition properties of the slow wind are thought to result from magnetic reconnection processes in the solar corona. We identify regions of enhanced variability and composition in the solar wind from 2003 April 15 to May 13 (Carrington Rotation 2002), observed by the Wind and Advanced Composition Explorer spacecraft, and demonstrate their relationship to the separatrix–web (hereafter, S-Web) structures describing the corona’s large-scale magnetic topology. There are four pseudostreamer (PS) wind intervals and two helmet streamer (HS) heliospheric current sheet/plasma sheet crossings (and an interplanetary coronal mass ejection), which all exhibit enhanced alpha-to-proton ratios and/or elevated ionic charge states of carbon, oxygen, and iron. We apply the magnetic helicity–partial variance of increments ( H m –PVI) procedure to identify coherent magnetic structures and quantify their properties during each interval. The mean duration of these structures are ∼1 hr in both the HS and PS wind. We find a modest enhancement above the power-law fit to the PVI waiting-time distribution in the HS-associated wind at the 1.5–2 hr timescales that is absent from the PS intervals. We discuss our results in the context of previous observations of the ∼90 minutes periodic density structures in the slow solar wind, further development of the dynamic S-Web model, and future Parker Solar Probe and Solar Orbiter joint observational campaigns. 

The exact coronal origin of the slow-speed solar wind has been under debate for decades in the Heliophysics community. Besides the solar wind speed, the heavy ion composition, including the elemental abundances and charge state ratios, are widely used as diagnostic tool to investigate the coronal origins of the slow wind. In this study, we recognize a subset of slow speed solar wind that is located on the upper boundary of the data distribution in the O7+/O6+ versus C6+/C5+ plot (O-C plot). In addition, in this wind the elemental abundances relative to protons, such as N/P, O/P, Ne/P, Mg/P, Si/P, S/P, Fe/P, He/P, and C/P are systemically depleted. We compare these winds (“upper depleted wind” or UDW hereafter) with the slow winds that are located in the main stream of the O-C plot and possess comparable Carbon abundance range as the depletion wind (“normal-depletion-wind”, or NDW hereafter). We find that the proton density in the UDW is about 27.5% lower than in the NDW. Charge state ratios of O7+/O6+, O7+/O, and O8+/O are decreased by 64.4%, 54.5%, and 52.1%, respectively. The occurrence rate of these UDW is anti-correlated with solar cycle. By tracing the wind along PFSS field lines back to the Sun, we find that the coronal origins of the UDW are more likely associated with quiet Sun regions, while the NDW are mainly associated with active regions and HCS-streamer.