Turbulence Characteristics of Switchbacks and Non-switchbacks Intervals Observed by Parker Solar Probe

Abstract:

In this work we use Parker Solar Probe (PSP) in-situ measurements to analyze the characteristics of solar wind turbulence during the first solar encounter near 36 solar radius. In this analysis we isolate so-called switchback (SB) intervals (folded magnetic field lines) from non-switchback (NSB) intervals, which mainly follow the Parker spiral field. We estimate the correlation functions and 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 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 Alfvenic fluctuations that are propagating in the sunward (anti-sunward) 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 generation mechanisms.