# In situ measurement of slow solar wind emerging from a pseudostreamer: a conjunction study with Parker Solar Probe and Solar Orbiter

**Authors:** Tamar Ervin, Stuart D. Bale, Samuel T. Badman, Yeimy J. Rivera, Orlando Romeo, Jia Huang, Pete Riley, Trevor A. Bowen, Susan T. Lepri, Ryan M. Dewey  
**arXiv:** [2309.07949](https://arxiv.org/abs/2309.07949)  
**Date:** 2023-09-14  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2309.07949v1/

## Key points

- Researchers aim to identify the source regions of the slow solar wind (SSW)
- They combine models with in situ observations
- Compositional diagnostics from the Solar Orbiter heavy ion sensor (HIS) are used
- Variations in composition provide insights into the origin and nature of the solar wind
- Potential Field Source Surface (PFSS) and Magnetohydrodynamic (MHD) models are used to connect observed plasma to its origin footpoint
- Comparison between model results and in situ measurements validate the study's techniques
- Heliospheric current sheet (HCS) crossing is evident, indicated by enhancements in various factors
- Fast wind from a small equatorial coronal hole (CH) exhibits specific characteristics
- Anomalously low alpha particle abundance is observed in fast wind from a CH
- Slow wind from different sources with variation in composition and Alfvenicity is identified
- Distinguishing between classical non-Alfvenic and high-Alfvenicity SSW is done based on specific factors
- Comprehensive analysis highlights the power of multi-instrument conjunction studies in assessing sources of solar wind

## Summary

In this study, the researchers aim to identify the source regions of the slow solar wind (SSW) by combining models with in situ observations. They take advantage of a fortuitous conjunction between the Solar Orbiter and Parker Solar Probe (PSP) during PSP Encounter 11 to include compositional diagnostics from the Solar Orbiter heavy ion sensor (HIS). These variations in composition provide crucial insights into the origin and nature of the solar wind. To connect the observed plasma at PSP and Solar Orbiter to its origin footpoint in the photosphere, the researchers use Potential Field Source Surface (PFSS) and Magnetohydrodynamic (MHD) models. They compare these model results with in situ measurements obtained by both spacecraft. The analysis reveals a very clear signature of a heliospheric current sheet (HCS) crossing, evidenced by enhancements in low first ionization potential (FIP) elements, ion charge state ratios, proton density, low-Alfvenicity, and polarity estimates. This validates the combination of modeling, data collection and mapping techniques used in this study. The researchers also investigate fast wind from a small equatorial coronal hole (CH), which exhibits characteristics such as low ion charge state ratios, low FIP bias, high-Alfvenicity and low footpoint brightness. While most of these characteristics fit together well for fast wind from a CH, there is an anomalously low alpha particle abundance observed. Furthermore, this study identifies slow wind from various different sources with broad variation in composition and Alfvenicity. The researchers distinguish between classical non-Alfvenic and high-Alfvenicity SSW. They associate low-Alfvenicity with decreased alpha-to-proton abundance; high charge state ratios; and FIP bias with streamer wind while intermediate alpha abundance; high-Alfvenicity; and dips in ion charge state ratios correspond to CH boundaries. Through this comprehensive analysis, the researchers highlight the power of multi-instrument conjunction studies in assessing sources of solar wind. By combining models with in situ observations and compositional diagnostics they are able to gain crucial insights into origin and nature of different types of solar wind. This study contributes to our understanding of complex dynamics and processes occurring within Sun's atmosphere as well as heliosphere.