Solar wind rotation rate and shear at coronal hole boundaries, possible consequences for magnetic field inversions

TL;DR

This study investigates the origins of magnetic field rotations and shear in the solar wind, linking coronal structures and boundary regions to the formation of magnetic switchbacks observed by Parker Solar Probe.

Contribution

It combines spacecraft measurements with MHD modeling to identify coronal sources of solar wind shear and magnetic deflections, revealing structured rotation and shear regions near coronal hole boundaries.

Findings

Coronal rotation is highly structured with enhanced shear near boundary regions.

A significant fraction of magnetic switchbacks originate from these shear regions.

Shear regions influence large-scale solar wind variability and magnetic field deflections.

Abstract

In-situ measurements by several spacecraft have revealed that the solar wind is frequently perturbed by transient structures (magnetic folds, jets, waves, flux-ropes) that propagate rapidly away from the Sun over large distances. Parker Solar Probe has detected frequent rotations of the magnetic field vector at small heliocentric distances, accompanied by surprisingly large solar wind rotation rates. The physical origin of such magnetic field bends, the conditions for their survival across the interplanetary space, and their relation to solar wind rotation are yet to be clearly understood. We traced measured solar wind flows from the spacecraft position down to the surface of the Sun to identify their potential source regions and used a global MHD model of the corona and solar wind to relate them to the rotational state of the low solar corona. We identified regions of the solar corona for which solar wind speed and rotational shear are important and long-lived, that can be favourable to the development of magnetic deflections and to their propagation across extended heights in the solar wind. We show that coronal rotation is highly structured and that enhanced flow shear develops near the boundaries between coronal holes and streamers, around and above pseudo-streamers, even when such boundaries are aligned with the direction of solar rotation. A large fraction of the switchbacks identified by PSP map back to these regions, both in terms of instantaneous magnetic field connectivity and of the trajectories of wind streams that reach the spacecraft. These regions of strong shears are likely to leave an imprint on the solar wind over large distances and to increase the transverse speed variability in the slow solar wind. The simulations and connectivity analysis suggest they can be a source of the switchbacks and spikes observed by Parker Solar Probe.