Turbulence characteristics of switchbacks and non-switchbacks intervals observed by \emph{Parker Solar Probe}

TL;DR

This study analyzes solar wind turbulence during Parker Solar Probe's first encounter, distinguishing switchback and non-switchback intervals, revealing differences in spectral indices, correlation lengths, and turbulence imbalance, shedding light on the nature of magnetic field foldings.

Contribution

It provides the first detailed comparison of turbulence characteristics between switchback and non-switchback intervals using in-situ measurements, highlighting their distinct spectral and correlation properties.

Findings

Magnetic power spectrum steeper in switchbacks (~-5/3) than non-switchbacks (~-3/2)

Backward Elsasser field decorrelation length larger in non-switchbacks

Switchbacks exhibit higher residual energy and sunward Alfvénic fluctuations

Abstract

We use \emph{Parker Solar Probe} (\emph{PSP}) in-situ measurements to analyze the characteristics of solar wind turbulence during the first solar encounter covering radial distances between $35.7R_\odot$ and $41.7R_\odot$. In our analysis we isolate so-called switchback (SB) intervals (folded magnetic field lines) from non-switchback (NSB) intervals, which mainly follow the Parker spiral field. Using a technique based on conditioned correlation functions, we estimate the power spectra of Elsasser, magnetic and bulk velocity fields separately in the SB and NSB intervals. In comparing the turbulent energy spectra of the two types of intervals, we find the following characteristics: 1) The decorrelation length of the backward-propagating Elsasser field $z^-$ is larger in the NSB intervals than the one in the SB intervals; 2) the magnetic power spectrum in SB intervals is steeper, with spectral index close to -5/3, than in NSB intervals, which have a spectral index close to -3/2; 3) both SB and NSB turbulence are imbalanced with NSB having the largest cross-helicity, 4) the residual energy is larger in the SB intervals than in NSB, and 5) the analyzed fluctuations are dominated by Alfv\'enic fluctuations that are propagating in the \emph{sunward} (\emph{anti-sunward}) direction for the SB (NSB) turbulence. These observed features provide further evidence that the switchbacks observed by \emph{PSP} are associated with folded magnetic field lines giving insight into their turbulence nature.