Switchbacks and their role in the turbulent cascade: Solar Orbiter observations

Abstract

Context. Magnetic switchbacks are large-amplitude magnetic field deflections of Alfvénic nature that are characterized by a high degree of correlation between the velocity and the magnetic field that are routinely detected in the inner heliosphere. Their timescales vary between hundreds of seconds to up to few hours, so that their role within the turbulent transfer of energy from large to small scales in the solar wind is a key question.Aims. We investigate the contribution of switchbacks to the turbulence cascade in the magnetic and velocity fields. The considered interval was taken within the rarefaction region of the first stream of slow Afvénic wind observed by Solar Orbiter in the inner heliosphere.Methods. The analysis was based on full-cadence measurements for the magnetic field vector from the fluxgate magnetometer MAG and reprocessed ion data sampled at a resolution of 4 s from the Proton and Alpha particle sensor (PAS) of the Solar Wind Analyser (SWA) suite. Alfvénicity, structure functions, and intermittency were evaluated to investigate the turbulence ands kinetic parameters to study the reaction of the plasma to the switchbacks.Results. Switchbacks are observed as isolated structures or in well-localized patches that are generated by two (or more) interacting structures that cover a range from magnetohydrodynamic to kinetic scales. In this interval of the slow Afvénic wind, they mainly affect the magnetic cascade in the radial direction (which in this sample is almost parallel to the mean field direction) not only in terms of the energy content across the scales, but also in terms of the inhomogeneity (i.e., intermittency), which play a role in transferring magnetic and kinetic energies across scales. Moreover, switchbacks are characterized by a high anticorrelation between the magnetic and velocity field components, which implies that these structures are regions of a local alignment of v and b. Finally, no equipartition between kinetic and magnetic energy is found, which suggests that the emergence of magnetic structures is already well consolidated at about 0.6 au.Conclusions. Our results in this interval of slow Afvénic wind suggest that an important role is played by switchbacks in the magnetic and velocity turbulent cascade in the flow direction. Moreover, by confirming and expanding previous features observed for a single case-study, our results support the idea that switchbacks strongly influence the surrounding plasma and play a different role on protons and alpha particles.