Source-dependent properties of two slow solar wind states

Abstract

Two states of the slow solar wind are identified from in-situ measurements by Parker Solar Probe (PSP) inside 50 solar radii from the Sun. At such distances the wind measured at PSP has not yet undergone significant transformation related to the expansion and propagation of the wind. We focus in this study on the properties of the quiet solar wind with no magnetic switchbacks. The two states differ by their plasma beta, flux and magnetic pressure. PSP's magnetic connectivity established with Potential Field Source Surface (PFSS) reconstructions, tested against extreme ultraviolet (EUV) and white-light imaging, reveals the two states correspond to a transition from a streamer to an equatorial coronal hole. The expansion factors of magnetic field lines in the streamer are 20 times greater than those rooted near the center of the coronal hole. The very different expansion rates of the magnetic field result in different magnetic pressures measured by PSP in the two plasma states. Solar wind simulations run along these differing flux tubes reproduce the slower and denser wind measured in the streamer and the more tenuous wind measured in the coronal hole. Plasma heating is more intense at the base of the streamer field lines rooted near the boundary of the equatorial hole than those rooted closer to the center of the hole. This results in a higher wind flux driven inside the streamer than deeper inside the equatorial hole.

arXiv commentAccepted for publication in the Astrophysical Journal on Feb 4, 2021

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• Total Electron Temperature Derived from Quasi-Thermal Noise Spectroscopy In the Pristine Solar Wind: Parker Solar Probe Observations
• Parker Solar Probe Observations of High Plasma Beta Solar Wind from Streamer Belt
• The S-Web Origin of Composition Enhancement in the Slow-to-Moderate Speed Solar Wind
• Solar wind rotation rate and shear at coronal hole boundaries, possible consequences for magnetic field inversions
• Flux-tube-dependent propagation of Alfvén waves in the solar corona
• Domains of Magnetic Pressure Balance in Parker Solar Probe Observations of the Solar Wind
• Testing the flux tube expansion factor -- solar wind speed relation with Solar Orbiter data