Magnetic field kinks and folds in the solar wind

TL;DR

This study uses numerical MHD simulations to investigate the evolution and persistence of magnetic switchbacks and radial jets in the solar wind, showing they can originate near the Sun and survive over large distances under certain conditions.

Contribution

It demonstrates through simulations that large amplitude Alfvénic fluctuations, including switchbacks and jets, can originate in the lower corona and persist in the solar wind for extended periods.

Findings

Switchbacks can last for hundreds of Alfvén crossing times before decay.

Persistence of switchbacks depends on a calm background solar wind.

Simulations align with PSP observations of magnetic field perturbations.

Abstract

Parker Solar Probe (PSP) observations during its first encounter at 35.7 $R_\odot$ have shown the presence of magnetic field lines which are strongly perturbed to the point that they produce local inversions of the radial magnetic field, known as switchbacks. Their counterparts in the solar wind velocity field are local enhancements in the radial speed, or jets, displaying (in all components) the velocity-magnetic field correlation typical of large amplitude Alfv\'en waves propagating away from the Sun. Switchbacks and radial jets have previously been observed over a wide range of heliocentric distances by Helios, WIND and Ulysses, although they were prevalent in significantly faster streams than seen at PSP. Here we study via numerical MHD simulations the evolution of such large amplitude Alfv\'enic fluctuations by including, in agreement with observations, both a radial magnetic field inversion and an initially constant total magnetic pressure. Despite the extremely large excursion of magnetic and velocity fields, switchbacks are seen to persist for up to hundreds of Alfv\'en crossing times before eventually decaying due to the parametric decay instability. Our results suggest that such switchback/jet configurations might indeed originate in the lower corona and survive out to PSP distances, provided the background solar wind is sufficiently calm, in the sense of not being pervaded by strong density fluctuations or other gradients, such as stream or magnetic field shears, that might destabilize or destroy them over shorter timescales.