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.
Highlights
Near-Sun solar wind observations by the Parker Solar Probe (PSP) during the first perihelion passes have revealed the frequent presence of the so-called magnetic switchbacks (SBs), which refer to local reversals of the radial magnetic field (Bale et al 2019; Kasper et al 2019; Dudok de Wit et al 2020; Horbury et al 2020; McManus et al 2020)
The power spectra that correspond to Elsasser fields z, velocity field V, and magnetic field B from these discontinuous SB and NSB intervals can be derived from their corresponding conditioned correlation functions
In this work we have used a methodology based on conditioned correlation functions to analyze the characteristics of the turbulence in the SB and NSB intervals at heliocentric distances from 35.7Re to 41.7Re
Summary
Near-Sun solar wind observations by the Parker Solar Probe (PSP) during the first perihelion passes have revealed the frequent presence of the so-called magnetic switchbacks (SBs), which refer to local reversals of the radial magnetic field (Bale et al 2019; Kasper et al 2019; Dudok de Wit et al 2020; Horbury et al 2020; McManus et al 2020) These switchbacks are usually associated with correlated enhancements of the radial plasma flow. A more recent study of proton core-beam reversals with PSP data shows that the proton core parallel temperature is the same inside and outside of switchbacks (Woolley et al 2020), indicating more evidence that Alfvénic pulses travel along open magnetic field lines Another important observed feature of SBs is that turbulence is dominated by sunward-propagating Alfvénic fluctuations over antisunward ones, an indication that Alfvénic fluctuations propagating away from the Sun are following folded magnetic field lines.
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