Turbulent generation of magnetic switchbacks in the Alfv\'enic solar wind

TL;DR

This study uses 3D simulations of solar wind to show that magnetic switchbacks observed by the Parker Solar Probe can naturally form from Alfvén wave turbulence, matching many observed properties.

Contribution

It demonstrates that magnetic switchbacks can emerge from Alfvén wave turbulence in the solar wind, providing a plausible physical mechanism consistent with observations.

Findings

Simulated switchbacks match observed properties like Alfvénic correlations and polarization.

Switchbacks are large-amplitude nonlinear Alfvén waves with magnetic discontinuities.

Simulation results align with Parker Solar Probe observations.

Abstract

One of the most important early results from the Parker Solar Probe (PSP) is the ubiquitous presence of magnetic switchbacks, whose origin is under debate. Using a three-dimensional direct numerical simulation of the equations of compressible magnetohydrodynamics from the corona to 40 solar radii, we investigate whether magnetic switchbacks emerge from granulation-driven Alfv\'en waves and turbulence in the solar wind. The simulated solar wind is an Alfv\'enic slow-solar-wind stream with a radial profile consistent with various observations, including observations from PSP. As a natural consequence of Alfv\'en-wave turbulence, the simulation reproduced magnetic switchbacks with many of the same properties as observed switchbacks, including Alfv\'enic v-b correlation, spherical polarization (low magnetic compressibility), and a volume filling fraction that increases with radial distance. The analysis of propagation speed and scale length shows that the magnetic switchbacks are large-amplitude (nonlinear) Alfv\'en waves with discontinuities in the magnetic field direction. We directly compare our simulation with observations using a virtual flyby of PSP in our simulation domain. We conclude that at least some of the switchbacks observed by PSP are a natural consequence of the growth in amplitude of spherically polarized Alfv\'en waves as they propagate away from the Sun.