Turbulence Characteristics of Switchback and Nonswitchback Intervals Observed by Parker Solar Probe

Abstract

Abstract We use Parker Solar Probe (PSP) in situ measurements to analyze the characteristics of solar wind turbulence during the first solar encounter covering radial distances between 35.7R ⊙ and 41.7R ⊙. In our analysis we isolate so-called switchback (SB) intervals (folded magnetic field lines) from nonswitchback (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 Alfvénic fluctuations that are propagating in the sunward (antisunward) direction for the SB (NSB) turbulence. These observed features provide further evidence that the switchbacks observed by PSP are associated with folded magnetic field lines giving insight into their turbulence nature.