The Sun’s Open–Closed Flux Boundary and the Origin of the Slow Solar Wind

Wilkins, Chloe P.; Pontin, David I.; Yeates, Anthony R.; Antiochos, Spiro K.; Schunker, Hannah; Lamichhane, Bishnu

Abstract

The Sun’s open–closed flux boundary (OCB) separates closed and open magnetic field lines, and is the site for interchange magnetic reconnection processes thought to be linked to the origin of the slow solar wind (SSW). We analyze the global magnetic field structure and OCB from 2010 December to 2019 December using three coronal magnetic field models: a potential-field source-surface (PFSS) model, a static equilibrium magnetofrictional model, and a time-dependent magnetofrictional model. We analyze the model and cycle dependence of the OCB length on the photosphere, as well as the magnetic flux in the vicinity of the OCB. Near solar maximum, the coronal magnetic field for each model consists predominantly of long, narrow coronal holes, and nearly all the open flux lies within 1 supergranule diameter (25 Mm) of the OCB. By comparing to interplanetary scintillation measurements of SSW speeds, we argue that the fraction of open flux within this 25 Mm band is a good predictor of the amount of SSW in the heliosphere. Importantly, despite its simplicity, we show that the PFSS model estimates this fraction as well as the time-dependent model. We discuss the implications of our results for understanding SSW origins and interchange reconnection at the OCB.

Citation

Wilkins, C. P., Pontin, D. I., Yeates, A. R., Antiochos, S. K., Schunker, H., & Lamichhane, B. (2025). The Sun’s Open–Closed Flux Boundary and the Origin of the Slow Solar Wind. The Astrophysical Journal, 985(2), Article 190. https://doi.org/10.3847/1538-4357/adcd65

• Journal Article Type: Article
• Acceptance Date: Apr 14, 2025
• Online Publication Date: May 23, 2025
• Publication Date: Jun 1, 2025
• Deposit Date: May 27, 2025
• Publicly Available Date: May 27, 2025
• Journal: The Astrophysical Journal
• Electronic ISSN: 1538-4357
• Peer Reviewed: Peer Reviewed
• Volume: 985
• Issue: 2
• Article Number: 190
• DOI: https://doi.org/10.3847/1538-4357/adcd65
• Keywords: Solar magnetic fields, Slow solar wind, Solar coronal holes, Solar corona
• Public URL: https://durham-repository.worktribe.com/output/3963599