Source-dependent properties of two slow solar wind states

TL;DR

This study identifies two distinct states of slow solar wind within 50 solar radii, linked to different magnetic structures and expansion rates, revealing how magnetic topology influences plasma properties close to the Sun.

Contribution

It demonstrates the source-dependent properties of slow solar wind states near the Sun and links them to magnetic topology and expansion factors using PSP data and simulations.

Findings

Two slow solar wind states differ by plasma beta, flux, and magnetic pressure.

The states correspond to a transition from streamer to coronal hole.

Magnetic expansion rates influence plasma heating and wind flux.

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.