Formation of Magnetic Switchbacks Observed by Parker Solar Probe

TL;DR

This paper presents a theory explaining the formation of magnetic switchbacks in the solar wind as resulting from shear of Alfvén waves, supported by analytic expressions and realistic solar wind scenarios.

Contribution

It introduces a simple, predictive theory for magnetic switchback formation based on shear of circularly polarized Alfvén waves, validated with analytic and realistic models.

Findings

Magnetic switchbacks are caused by shear of Alfvén waves.

Analytic expression for magnetic field variation is provided.

The mechanism is effective in realistic solar wind conditions.

Abstract

Magnetic switchbacks are rapid high amplitude reversals of the radial magnetic field in the solar wind that do not involve a heliospheric current sheet crossing. First seen sporadically in the seventies in Mariner and Helios data, switchbacks were later observed by the Ulysses spacecraft beyond 1 au and have been recently identified as a typical component of solar wind fluctuations in the inner heliosphere by the Parker Solar Probe spacecraft. Here we provide a simple yet predictive theory for the formation of these magnetic reversals: the switchbacks are produced by the shear of circularly polarized Alfv\'en waves by a transversely varying radial wave propagation velocity. We provide an analytic expression for the magnetic field variation, establish the necessary and sufficient conditions and show that the mechanism works in a realistic solar wind scenario.