Switchbacks: statistical properties and deviations from alfv\'enicity

TL;DR

This study analyzes the statistical properties and boundaries of solar wind switchbacks, revealing their mostly alfvénic nature, compressibility, and potential links to instabilities like the firehose, providing insights into their generation mechanisms.

Contribution

It offers a detailed statistical and boundary analysis of switchbacks, highlighting their alfvénic and compressible features and proposing possible generation mechanisms.

Findings

73% of switchbacks are alfvénic

27% are compressible

Boundaries resemble rotational or tangential discontinuities

Abstract

{Parker Solar Probe's first solar encounter has revealed the presence of sudden magnetic field deflections that are called switchbacks and are associated with proton velocity enhancements in the slow alfv\'{e}nic solar wind.} {We study their statistical properties with a special focus on their boundaries.} {Using data from SWEAP and FIELDS we investigate particle and wavefield properties. The magnetic boundaries are analyzed with the minimum variance technique.} {Switchbacks are found to be alfv\'{e}nic in 73\% of the cases and compressible in 27\%. The correlations between magnetic field magnitude and density fluctuations reveal the existence of both positive and negative correlations, and the absence of perturbations of the magnetic field magnitude. Switchbacks do not lead to a magnetic shear in the ambient field. Their boundaries can be interpreted in terms of rotational or tangential discontinuities. The former are more frequent.} {Our findings provide constraints on the possible generation mechanisms of switchbacks, which has to be able to account also for structures that are not purely alfv\'{e}nic. One of the possible candidates, among others, manifesting the described characteristics is the firehose instability.}